Subj : Weather Glossary (S)
To : All
From : Daryl Stout
Date : Sat Apr 20 2019 12:09 am
This weather glossary contains information on more than 2000 terms,
phrases and abbreviations used by the National Weather Service (NWS)...
the government agency who makes weather forecasts, and issues weather
advisories, watches, and warnings, for the United States, and its
territories.
Many of these terms and abbreviations are used by NWS forecasters to
communicate between each other and have been in use for many years and
before many NWS products were directly available to the public. It is the
purpose of this glossary to aid you in better understanding NWS products.
***
S
1) South
or
2) Snow
S-Band Radar
These were in use as network radars in the National Weather Service prior
to the installation of the WSR 88-D radars. They were 10-centimeter
wavelength radars.
S/W
Shortwave - a disturbance in the mid or upper part of the atmosphere which
induces upward motion ahead of it. If other conditions are favorable, the
upward motion can contribute to thunderstorm development ahead of a
shortwave.
S/WV
Shortwave - a disturbance in the mid or upper part of the atmosphere which
induces upward motion ahead of it. If other conditions are favorable, the
upward motion can contribute to thunderstorm development ahead of a
shortwave.
SafetyNET
Inmarsat-C SafetyNET is an internationally adopted, automated satellite
system for promulgating weather forecasts and warnings, marine
navigational warnings and other safety related information to all types
vessels and is part of the Global Maritime Distress and Safety System
(GMDSS).
Saffir-Simpson Scale
This scale was developed in an effort to estimate the possible damage a
hurricane's sustained winds and storm surge could do to a coastal area.
The scale of numbers are based on actual conditions at some time during
the life of the storm. As the hurricane intensifies or weakens, the scale
number is reassessed accordingly. The following table shows the scale
broken down by category, central pressure, winds, and storm surge:
Cat. Cntrl Pres. (mb) Wind (mph) Storm Surge (ft.) Damage
1 980 or > 74 - 95 4 - 5 Minimal
2 965 - 979 96 - 110 6 - 8 Moderate
3 945 - 964 111 - 130 9 - 12 Extensive
4 920 - 944 131 - 155 13 - 18 Extreme
5 < 920 > 155 > 18 Catastrophic
Salinity (SAL)
In oceanography, conductivity is measured and converted to salinity by
a known functional relationship between the measured electrical
conductivity of seawater temperature and pressure.
SAME
(Specific Area Message Encoding) - A tone alert system which allows NOAA
Weather Radio receivers equipped with the SAME feature to sound an alert
for only certain weather conditions or within a limited geographic area
such as a county.
SAMEX
Storm and Mesoscale Ensemble Experiment
Sampling Frequency
The rate at which sensor data is read or sampled.
Sandstorm
Particles of sand carried aloft by strong wind. The sand particles are
mostly confined to the lowest ten feet, and rarely rise more than fifty
feet above the ground.
Santa Ana Wind
In southern California, a weather condition in which strong, hot,
dust-bearing winds descend to the Pacific Coast around Los Angeles from
inland desert regions.
Sastrugi
Ridges of snow formed on a snow field by the action of the wind.
SAT
1. Satellite (imagery)
2. Saturday
Satellite Hydrology Program
A NOHRSC program that uses satellite data to generate areal extent of
snow cover data over large areas of the western United States.
SATL
Satellite
Saturation Vapor Pressure
The vapor pressure of a system, at a given temperature, wherein the
vapor of a substance is in equilibrium with a plane surface of that
substance's pure liquid or solid phase.
SAWRS
Supplementary Aviation Reporting Station - the SAWRS program addresses
the concerns of users who depend on weather observations for air
operations. If the cooperator is collocated with a commissioned
automated system, they ensure continuity during outage periods of the
automated system. The requirement for a SAWRS arises from the FAA
validated need for observations to satisfy FAR 121 or 135 operations
or for the safe conduct of other aircraft.
SBCAPE
Surface Based CAPE; CAPE calculated using a Surface based parcel.
SBND
Southbound
SBSD
Subside
SC
Stratocumulus
SCA
Small Craft Advisory
Scattered
Precipitation descriptor: Areal coverage of convective weather
affecting 30 percent to 50 percent of a forecast zone (s). Sky
coverage descriptor : A sky coverage of 1/8 through 4/8.
In U.S. weather observing procedures, this is reported with the
contraction SCT.
Scattering
The process in which a beam of light is diffused or deflected by
collisions with particles suspended in the atmosphere.
SCT
Scattered
Scud
Small, ragged, low cloud fragments that are unattached to a larger
cloud base and often seen with and behind cold fronts and thunderstorm
gust fronts. Such clouds generally are associated with cool moist air,
such as thunderstorm outflow.
SE
Southeast
Sea Breeze
A thermally produced wind blowing during the day from a cool ocean
surface onto the adjoining warm land, caused by the difference in the
rates of heating of the surfaces of the ocean and of the land.
Sea Breeze Convergence Zone
The zone at the leading edge of a sea breeze where winds converge. The
incoming air rises in this zone, often producing convective clouds.
Sea Breeze Front
The leading edge of a sea breeze, whose passage is often accompanied
by showers, a wind shift, or a sudden drop in temperature.
Sea Fog
Common advection fog caused by transport of moist air over a cold body
of water.
Sea Ice
Any form of ice found at sea which has originated from the freezing of
sea water (sea ice does NOT include superstructure icing). Ice formed
from the freezing of the waters of the Great Lakes will be considered
the same as sea ice.
Sea Level Pressure
The sea level pressure is the atmospheric pressure at sea level at a
given location. When observed at a reporting station that is not at sea
level (nearly all stations), it is a correction of the station pressure
to sea level. This correction takes into account the standard variation
of pressure with height and the influence of temperature variations
with height on the pressure. The temperature used in the sea level
correction is a twelve hour mean, eliminating diurnal effects. Once
calculated, horizontal variations of sea level pressure may be compared
for location of high and low pressure areas and fronts.
Sea Surface Temperatures
The term refers to the mean temperature of the ocean in the upper few
meters.
Seas
The combination of both wind waves and swell. Used to describe the
combination or interaction of wind waves and swell in which the
separate components are not distinguished. This includes the case when
swell is negligible or is not considered in describing sea state.
Specifically, Seas2 = S2+W2 where S is the height of the swell and W is
the height of the wind wave. When used, Seas should be considered as
being the same as the Significant Wave Height.
Second-Day Feet
In hydrologic terms, the volume of water represented by a flow of one
cubic foot per second for 24 hours; equal to 86,400 cubic feet. This is
used extensively as a unit of runoff volume. Often abbreviated as SDF.
Secondary Ambient Air Quality Standards
Air quality standards designed to protect human welfare, including the
effects on vegetation and fauna, visibility and structures.
Secondary Pollutant
Pollutants generated by chemical reactions occurring within the
atmosphere. Compare primary pollutant.
Sector Boundary
In solar-terrestrial terms, in the solar wind, the area of demarcation
between sectors, which are large-scale features distinguished by the
predominant direction of the interplanetary magnetic field, toward or
away from the sun.
Sector Visibility
The visibility in a specific direction that represents at least a 45�
arc of a horizontal circle.
Sectorized Hybrid Scan
A single reflectivity scan composed of data from the lowest four
elevation scans. Close to the radar, higher tilts are used to reduce
clutter. At further ranges, either the maximum values from the lowest two
scans are used or the second scan values are used alone.
Securite
A headline within National Weather Service high seas forecasts transmitted
via the GMDSS to indicate that no hurricane or hurricane force winds are
forecast.
Sediment Storage Capacity
In hydrologic terms, the volume of a reservoir planned for the deposition
of sediment.
Seepage
In hydrologic terms, the interstitial movement of water that may take
place through a dam, its foundation, or abutments.
Seiche
A standing wave oscillation of water in large lakes usually created by
strong winds and/or a large barometric pressure gradient.
SEL
A watch cancellation statement issued to terminate a watch before its
original expiration time.
SELS
Severe Local Storm
SELY
Southeasterly
Sensible Heat Flux
The flux of heat from the earth's surface to the atmosphere that is not
associated with phase changes of water; a component of the surface
energy budget.
Separation Eddy
An eddy that forms near the ground on the windward or leeward side of a
bluff object or steeply rising hillside; streamlines above this eddy go
over the object.
Serial Derecho
Type of derecho that consists of an extensive squall line which is
oriented such that the angle between the mean wind direction and the
squall line axis is small. A series of LEWPs and bow echoes move along
the line. The downburst activity is associated with the LEWPs and bows.
A Serial Derecho tends to be more frequent toward the north end of the
line during the late winter and spring months. It occurs less
frequently than its cousin the "progressive derecho."
It is associated with a linear type mesoscale convective system that
moves along and in advance of a cold front or dry line. These boundaries
are often associated with a strong, migratory surface low pressure
system and strong short wave trough at 500 mb (strong dynamic forcing).
Lifted Indices are typically -6 or lower and the advection of dry air
in the mid-troposphere (3-7 km above ground) by relatively strong winds
leads to high convective instability and increased downdraft potential.
The bow echoes move along the line in the direction of the mean flow,
often southwest to northeast. These storms move at speeds exceeding 35
knots. Squall line movement is often less than 30 knots.
SERN
Southeastern
Service Hydrologist
The designated expert of the hydrology program at a WFO.
Servo Loop
In radar meteorology, a generic description of hardware needed to
remotely control the motion of the antenna dish.
Set
The direction towards which a current is headed. For example, a current
moving from west to east is said to be set to east.
Set-up
The process whereby strong winds blowing down the length of a lake cause
water to "pile up" at the downwind end, raising water levels there and
lowering them at the upwind end of the lake.
Severe Icing
The rate of ice accumulation on an aircraft is such that
de-icing/anti-icing equipment fails to reduce or control the hazard.
Immediate diversion is necessary.
Severe Local Storm
A convective storm that usually covers a relatively small geographic
area, or moves in a narrow path, and is sufficiently intense to threaten
life and/or property. Examples include severe thunderstorms with large
hail, damaging wind, or tornadoes. Although cloud-to-ground lightning is
not a criteria for severe local storms, it is acknowledged to be highly
dangerous and a leading cause of deaths, injuries, and damage from
thunderstorms. A thunderstorm need not be severe to generate frequent
cloud-to-ground lightning. Additionally, excessive localized convective
rains are not classified as severe storms but often are the product of
severe local storms. Such rainfall may result in related phenomena
(flash floods) that threaten life and property.
Severe Local Storm Watch
An alert issued by the National Weather Service for the contiguous U.S.
and its adjacent waters of the potential for severe thunderstorms or
tornadoes.
Severe Thunderstorm
A thunderstorm that produces a tornado, winds of at least 58 mph
(50 knots), and/or hail at least 3/4" in diameter. Structural wind damage
may imply the occurrence of a severe thunderstorm. A thunderstorm wind
equal to or greater than 40 mph (35 knots) and/or hail of at least 1/2"
is defined as approaching severe.
Severe Thunderstorm Warning
This is issued when either a severe thunderstorm is indicated by the
WSR-88D radar or a spotter reports a thunderstorm producing hail 3/4 inch
or larger in diameter and/or winds equal or exceed 58 miles an hour;
therefore, people in the affected area should seek safe shelter
immediately. Severe thunderstorms can produce tornadoes with little or no
advance warning. Lightning frequency is not a criteria for issuing a
severe thunderstorm warning. They are usually issued for a duration of
one hour. They can be issued without a Severe Thunderstorm Watch being
already in effect.
Like a Tornado Warning, the Severe Thunderstorm Warning is issued by
your National Weather Service Forecast Office (NWFO). Severe Thunderstorm
Warnings will include where the storm was located, what towns will be
affected by the severe thunderstorm, and the primary threat associated
with the severe thunderstorm warning. If the severe thunderstorm will
affect the nearshore or coastal waters, it will be issued as the combined
product--Severe Thunderstorm Warning and Special Marine Warning. If the
severe thunderstorm is also causing torrential rains, this warning may
also be combined with a Flash Flood Warning. If there is an ampersand
(&) symbol at the bottom of the warning, it indicates that the warning
was issued as a result of a severe weather report.
After it has been issued, the affected NWFO will follow it up
periodically with Severe Weather Statements. These statements will
contain updated information on the severe thunderstorm and they will
also let the public know when the warning is no longer in effect.
Severe Thunderstorm Watch
This is issued by the National Weather Service when conditions are
favorable for the development of severe thunderstorms in and close to
the watch area. A severe thunderstorm by definition is a thunderstorm
that produces 3/4 inch hail or larger in diameter and/or winds equal or
exceed 58 miles an hour. The size of the watch can vary depending on the
weather situation. They are usually issued for a duration of 4 to 8
hours. They are normally issued well in advance of the actual occurrence
of severe weather. During the watch, people should review severe
thunderstorm safety rules and be prepared to move a place of safety if
threatening weather approaches.
A Severe Thunderstorm Watch is issued by the Storm Prediction Center in
Norman, Oklahoma. Prior to the issuance of a Severe Thunderstorm Watch,
SPC will usually contact the affected local National Weather Service
Forecast Office (NWFO) and they will discuss what their current thinking
is on the weather situation. Afterwards, SPC will issue a preliminary
Severe Thunderstorm Watch and then the affected NWFO will then adjust
the watch (adding or eliminating counties/parishes) and then issue it
to the public by way of a Watch Redefining Statement. During the watch,
the NWFO will keep the public informed on what is happening in the
watch area and also let the public know when the watch has expired or
been cancelled.
Severe Weather Analysis
This WSR-88D radar product provides 3 base products (reflectivity (SWR),
radial velocity (SWV), and spectrum width (SWW)) at the highest
resolution available along with radial shear (SWS). These products are
mapped into a 27 nm by 27 nm region centered on a point which the
operator can specify anywhere within a 124 nm radius of the radar. It
is most effective when employed as an alert paired product with the
product centered on alert at height that caused the alert. It is used
to examine 3 base products simultaneously in a 4 quadrant display; and
analyze reflectivity and velocity products at various heights to gain a
comprehensive vertical analysis of the thunderstorm.
Severe Weather Potential Statement
This statement is designed to alert the public and state/local agencies
to the potential for severe weather up to 24 hours in advance. It is
issued by the local National Weather Service office.
Severe Weather Probability
This WSR-88D radar product algorithm displays numerical values
proportional to the probability that a storm will produce severe
weather within 30 minutes. Values determined using a statistical
regression equation which analyzes output from the VIL algorithm. It
is used to quickly identify the most significant thunderstorms.
Severe Weather Statement
A National Weather Service product which provides follow up information
on severe weather conditions (severe thunderstorm or tornadoes) which
have occurred or are currently occurring.
SEWD
Southeastward
SFC
Surface
Sferic
In solar-terrestrial terms, a transient electric or magnetic field
generated by any feature of lightning discharge (entire flash).
SG
Snow grains
SGFNT
Significant
Shallow Fog
Fog in which the visibility at 6 feet above ground level is 5/8ths
statute mile or more and the apparent visibility in the fog layer is
less than 5/8ths statute mile.
SHARS
Subtle Heavy Rainfall Signature
Shear
Variation in wind speed (speed shear) and/or direction (directional
shear) over a short distance within the atmosphere. Shear usually
refers to vertical wind shear, i.e., the change in wind with height,
but the term also is used in Doppler radar to describe changes in
radial velocity over short horizontal distances.
Sheet Flow
In hydrologic terms, flow that occurs overland in places where there
are no defined channels, the flood water spreads out over a large area
at a uniform depth. This also referred to as overland flow.
Sheet ice
Ice formed by the freezing of liquid precipitation or the freezing of
melted solid precipitation (see snow depth).
Shelf Cloud
A low, horizontal wedge-shaped arcus cloud, associated with a
thunderstorm gust front (or occasionally with a cold front, even in
the absence of thunderstorms). Unlike the roll cloud, the shelf cloud
is attached to the base of the parent cloud above it (usually a
thunderstorm). Rising cloud motion often can be seen in the leading
(outer) part of the shelf cloud, while the underside often appears
turbulent, boiling, and wind-torn.
SHFT
Shift
SHLW
Shallow
Shore ice
In hydrologic terms, an ice sheet in the form of a long border attached
to the bank or shore.; border ice.
Short Term Forecast
A product used to convey information regarding weather or hydrologic
events in the next few hours.
Short Wave Fade (SWF)
In solar-terrestrial terms, a particular ionospheric solar flare effect
under the broad category of sudden ionospheric disturbances (SIDs)
whereby short-wavelength radio transmissions, VLF, through HF, are
absorbed for a period of minutes to hours.
Short-Fuse Warning
A warning issued by the NWS for a local weather hazard of relatively
short duration. Short-fuse warnings include tornado warnings, severe
thunderstorm warnings, and flash flood warnings. Tornado and severe
thunderstorm warnings typically are issued for periods of an hour or
less, flash flood warnings typically for three hours or less.
Shortwave
Also known as Shortwave Trough; a disturbance in the mid or upper part
of the atmosphere which induces upward motion ahead of it. If other
conditions are favorable, the upward motion can contribute to
thunderstorm development ahead of a shortwave.
Shortwave Radiation
In solar-terrestrial terms, shortwave radiation is a term used to
describe the radiant energy emitted by the sun in the visible and
near-ultraviolet wavelengths (between about 0.1 and 2 micrometers).
Shortwave Trough
Also called Shortwave; A disturbance in the mid or upper part of the
atmosphere which induces upward motion ahead of it. If other conditions
are favorable, the upward motion can contribute to thunderstorm
development ahead of a shortwave trough.
Showalter Index
(Abbrev. SWI) - a stability index used to determine thunderstorm
potential. The SWI is calculated by lifting an air parcel adiabatically
from 850 mb to 500 mb. The algebraic difference between the air parcel
and the environmental temperature at 500 mb represents the SWI. It is
especially useful when you have a shallow cool airmass below 850 mb
concealing greater convective potential aloft. However, the SWI will
underestimate the convective potential for cool layers extending above
850 mb. It also does not take in account diurnal heating or moisture
below 850 mb. As a result, one must be very careful when using this
index.
Shower(s)
A descriptor, SH, used to qualify precipitation characterized by the
suddenness with which they start and stop, by the rapid changes of
intensity, and usually by rapid changes in the appearance of the sky.
SHRA
Rain showers
SHRAS
showers
SHRT
Short
SHRTWV
Shortwave - a disturbance in the mid or upper part of the atmosphere
which induces upward motion ahead of it. If other conditions are
favorable, the upward motion can contribute to thunderstorm
development ahead of a shortwave.
SHSN
Snow showers
SHWR
Shower
Sidelobe
A secondary energy maximum located outside the main radar beam.
Typically, it contains a small percentage of energy compared to the
main lobe, but it may produce erroneous echoes.
SIGMET
Significant Meteorological Advisory
Signal-to-Noise Ratio
A ratio that measures the comprehensibility of data, usually expressed
as the signal power divided by the noise power, usually expressed in
decibels (dB).
Significant Wave Height
The mean or average height of the highest one third of all waves in a
swell train or in a wave generating region. It approximates the value
an experienced observer would report if visually estimating sea height.
When expressed as a range (e.g. Seas 2-4 ft) , indicates a degree of
uncertainty in the forecast and/or expected changing conditions (not
that all waves are between 2-4 ft). Generally, it is assumed that
individual wave heights can be described using a Rayleigh distribution.
Example: Significant Wave Height = 10 ft 1 in 10 waves will be larger
than 11 ft 1 in 100 waves will be larger than 16 ft 1 in 1000 waves will
be larger than 19 ft
Therefore, assuming a wave period of 8 seconds, for a significant wave
height of 10 feet, a wave 19 feet or higher will occur every 8,000
seconds (2.2 hours).
Significant Weather Outlook
A narrative statement produced by the National Weather Service,
frequently issued on a routine basis, to provide information regarding
the potential of significant weather expected during the next 1 to 5
days.
SIGWX
Significant Weather
Single Cell Thunderstorm
This type of thunderstorm develops in weak vertical wind shear
environments. On a hodograph, this would appear as a closely grouped
set of random dots around the center of the graph. They are
characterized by a single updraft core and a single downdraft that
descends into the same area as the updraft. The downdraft and its
outflow boundary then cut off the thunderstorm inflow. This causes
the updraft and the thunderstorm to dissipate. Single cell thunderstorms
are short-lived. They only last about 1/2 hour to an hour. These
thunderstorms will occasionally become severe (3/4 inch hail, wind
gusts in the excess of 58 miles an hour, or a tornado), but only
briefly. In this case, they are called Pulse Severe Thunderstorms.
SITOR
(SImplex Teletype Over Radio) - a means of transmitting text broadcasts
over radio. The U.S. Coast Guard SITOR broadcast of NWS forecasts is
performed in mode B, FEC. SITOR is also known as Narrow Band Direct
Printing (NBDP). SITOR/NBDP is an automated direct service similar to
NAVTEX, but does not offer all of the same functionality such as
avoiding repeated messages.
Sky Condition
Used in a forecast to describes the predominant/average sky condition
based upon octants (eighths) of the sky covered by opaque (not
transparent) clouds.
Sky Condition Cloud Coverage
Clear / Sunny 0/8
Mostly Clear / Mostly Sunny 1/8 to 2/8
Partly Cloudy / Partly Sunny 3/8 to 4/8
Mostly Cloudy / Considerable Cloudiness 5/8 to 7/8
Cloudy 8/8
Fair (mainly for night) Less than 4/10 opaque clouds, no precipitation,
no extremes of visibility/temperature/wind
SKYWARN
A nationwide network of volunteer weather spotters who report to and are
trained by the National Weather Service. These spotters report many forms
of significant or severe weather such as Severe Thunderstorms, Tornadoes,
Hail, Heavy Snow, or Flooding. Contact your local National Weather Service
Forecast Office to learn about SKYWARN activities in your area.
SL
Sea Level
SLD
Solid
Sleet
(PL) - Sleet is defined as pellets of ice composed of frozen or mostly
frozen raindrops or refrozen partially melted snowflakes. These pellets
of ice usually bounce after hitting the ground or other hard surfaces.
Heavy sleet is a relatively rare event defined as an accumulation of
ice pellets covering the ground to a depth of 1" or more.
Sleet Warning
Issued when accumulation of sleet in excess of 1/2" is expected; this is
a relatively rare scenario. Usually issued as a winter storm warning for
heavy sleet.
SLGT
Slight
Slight Chance
In probability of precipitation statements, usually equivalent to a 20
percent chance.
Slight Risk
(of severe thunderstorms)- Severe thunderstorms are expected to affect
between 2 and 5 percent of the area. A slight risk generally implies that
severe weather events are expected to be isolated.
Sling Psychrometer
An instrument used to measure the water vapor content of the atmosphere
in which wet and dry bulb thermometers are mounted on a frame connected
to a handle at one end by means of a bearing or a length of chain. The
psychrometer is whirled by hand to provide the necessary ventilation to
evaporate water from the wet bulb.
SLO
Slow
SLOSH
(Sea, Lake and Overland Surges from Hurricanes) - A computer model run
by the National Hurricane Center (NHC) to estimate storm surge heights
resulting from historical, hypothetical, or predicted hurricanes by
taking into account pressure, size, forward speed, track, and winds.
SLP
Sea Level Pressure
SLT
1. Slight (as in "slight chance")
2. Sleet
SLY
Southerly
SM
1) Statute Miles
2) Sum total for month
SMA
The Soil Moisture Accounting Model.
Small Craft
There is no precise definition for small craft. Any vessel that may be
adversely affected by Small Craft Advisory criteria should be considered
a small craft. Other considerations include the experience of the vessel
operator, and the type, overall size, and sea worthiness of the vessel.
See Small Craft Advisory.
Small Craft Advisory
(SCA) - An advisory issued by coastal and Great Lakes Weather Forecast
Offices (WFO) for areas included in the Coastal Waters Forecast or
Nearshore Marine Forecast (NSH) products. Thresholds governing the
issuance of small craft advisories are specific to geographic areas. A
Small Craft Advisory may also be issued when sea or lake ice exists that
could be hazardous to small boats. There is no precise definition of a
small craft. Any vessel that may be adversely affected by Small Craft
Advisory criteria should be considered a small craft. Other
considerations include the experience of the vessel operator, and the
type, overall size, and sea worthiness of the vessel.
Eastern (ME..SC, Lake Erie, Lake Ontario) - Sustained winds or frequent
gusts ranging between 25 and 33 knots (except 20 to 25 knots, lower
threshold area dependent, to 33 knots for harbors, bays, etc.) and/or
seas or waves 5 to 7 feet and greater, area dependent.
Central (MN..OH) - Sustained winds or frequent gusts (on the Great Lakes)
between 22 and 33 knots inclusive, and/or seas or waves greater than 4 feet.
Southern (GA..TX and Caribbean) - Sustained winds of 20 to 33 knots,
and/or forecast seas 7 feet or greater that are expected for more than 2
hours.
Western (WA..CA) - Sustained winds of 21 to 33 knots, potentially in
combination with wave heights exceeding 10 feet (or wave steepness values
exceeding local thresholds).
Alaska (AK) - Sustained winds or frequent gusts of 23 to 33 knots. A small
craft advisory for rough seas may be issued for sea/wave conditions
deemed locally significant, based on user needs, and should be no lower
than 8 feet.
Hawaii (HI), Samoa - Sustained winds 25 knots or greater and seas 10 feet
or greater.
Guam and the Northern Mariana Islands - Sustained winds 22 to 33 knots
and/or combined seas of 10 feet or more.
"Frequent gusts" are typically long duration conditions (greater than 2
hours).
For a list of NWS Weather Offices by Region, refer to the following
website:
http://www.nws.noaa.gov/organization.php
Small Craft Advisory for Hazardous Seas
(SCAHS) - An advisory issued by coastal and Great Lakes Weather Forecast
Offices (WFO). This advisory may be issued within the Coastal Waters
Forecast or Nearshore Marine Forecast products. This advisory may be
issued when wind speeds are lower than small craft advisory criteria,
yet waves or seas are potentially hazardous due to wave period,
steepness, or swell direction. Thresholds governing the issuance of
Small Craft Advisories for Hazardous Seas are specific to geographic
areas.
Eastern (ME..SC, Lake Erie, Lake Ontario) - Seas or waves 5 to 7 feet
and greater, area dependent.
Central (MN..OH) - Seas or waves greater than 4 feet.
Southern (GA..TX and Caribbean) - Seas 7 feet or greater that are
expected for more than 2 hours.
Western (WA..CA) - Seas 10 feet or greater; or wave steepness values
exceeding local criteria.
Alaska (AK) - Seas or wave conditions deemed locally significant, based
on user needs, and should be no lower than 8 feet.
Hawaii (HI), Samoa - Seas 10 feet or greater.
Guam and the Northern Mariana Islands - Combined seas of 10 feet or more.
Small Craft Advisory for Rough Bar
(SCARB): An advisory issued by coastal and Great Lakes Weather Forecast
Offices (WFO) for specialized areas near harbor or river entrances known
as bars. This advisory may be included within the Coastal Waters Forecast
or Nearshore Marine Forecast products. Waves in or near such bars may be
especially hazardous to mariners due to the interaction of swell, tidal
or river currents in relatively shallow water. Thresholds governing the
issuance of Small Craft Advisories for Rough Bar are specific to local
geographic areas, and are based upon parameters such as wave steepness,
wind speed and direction, and local bathymetry.
Small Craft Advisory for Winds
(SCAW): An advisory issued by coastal and Great Lakes Weather Forecast
Offices (WFO). This advisory may be included in the Coastal Waters
Forecast or Nearshore Marine Forecast products. This advisory may be
issued when wave heights are lower than small craft advisory criteria,
yet wind speeds are potentially hazardous. Thresholds governing the
issuance of small craft advisories are specific to geographic areas.
Eastern (ME..SC, Lake Erie, Lake Ontario) - Sustained winds ranging
between 25 and 33 knots (except 20 to 25 knots, lower threshold area
dependent, to 33 knots for harbors, bays, etc.)
Central (MN..OH) - Sustained winds or frequent gusts (on the Great Lakes)
between 22 and 33 knots inclusive.
Southern (GA..TX and Caribbean) - Sustained winds of 20 to 33 knots that
are expected for more than 2 hours.
Western (WA..CA) - Sustained winds of 21 to 33 knots.
Alaska (AK) - Sustained winds or frequent gusts of 23 to 33 knots.
Pacific (HI, Guam, etc) - Sustained winds 25 knots or greater; except in
Guam where it is sustained winds of 22 to 33 knots.
Small Craft Should Exercise Caution
Precautionary statement issued to alert mariners with small, weather
sensitive boats.
Small Hail
Technically used to refer to snow pellets or graupel.
Small Stream Flooding
In hydrologic terms, flooding of small creeks, streams, or runs.
Smog
Originally smog meant a mixture of smoke and fog. Now, it means air that
has restricted visibility due to pollution or pollution formed in the
presence of sunlight--photochemical smog.
Smoke
(abbrev. K) Smoke in various concentrations can cause significant
problems for people with respiratory ailments. It becomes a more
universal hazard when visibilities are reduced to 1/2 mile or less.
Smoke Dispersal
Describes the ability of the atmosphere to ventilate smoke. Depends on
the stability and winds in the lower layers of the atmosphere, i.e.,
a combination of mixing heights and transport winds.
Smoke Management
The use of meteorology, fuel moisture, fuel loading, fire suppression
and burn techniques to keep smoke impacts from prescribed fires within
acceptable limits.
Smoothed Sunspot Number
An average of 13 monthly RI numbers, centered on the month of concern.
SMW
(Special Marine Warning) - A warning product issued for potentially
hazardous weather conditions usually of short duration (up to 2 hours)
producing sustained marine thunderstorm winds or associated gusts of
34 knots or greater; and/or hail 3/4 inch or more in diameter; and/or
waterspouts affecting areas included in a Coastal Waters Forecast, a
Nearshore Marine Forecast, or an Great Lakes Open Lakes Forecast that
is not adequately covered by existing marine warnings. Also used for
short duration mesoscale events such as a strong cold front, gravity
wave, squall line, etc., lasting less than 2 hours and producing winds
or gusts of 34 knots or greater.
SN
snow
Snotel
SNOw TELemetry - An automated network of snowpack data collection sites.
The Natural Resources Conservation Service (NRCS), formerly the Soil
Conservation Service (SCS), has operated the Federal-State-Private
Cooperative Snow Survey Program in the western United States since 1935.
A standard SNOTEL site consists of a snow pillow, a storage type
precipitation gage, air temperature sensor and a small shelter for
housing electronics.
Snow
Precipitation in the form of ice crystals, mainly of intricately
branched, hexagonal form and often agglomerated into snowflakes, formed
directly from the freezing [deposition] of the water vapor in the air.
Snow Accumulation and Ablation Model
In hydrologic terms, a model which simulates snow pack accumulation,
heat exchange at the air-snow interface, areal extent of snow cover,
heat storage within the snow pack, liquid water retention, and
transmission and heat exchange at the ground-snow interface.
Snow Advisory
This product is issued by the National Weather Service when a low
pressure system produces snow that may cause significant inconveniences,
but do not meet warning criteria and if caution is not exercised could
lead to life threatening situations. The advisory criteria varies from
area to area. If the forecaster feels that it is warranted, he or she
can issued it for amounts less than the minimum criteria. For example,
it may be issued for the first snow of the season or when snow has not
fallen in long while.
Snow Core
A sample of either freshly fallen snow, or the combined old and new snow
on the ground. This is obtained by pushing a cylinder down through the
snow layer and extracting it.
Snow Cornice
A mass of snow or ice projecting over a mountain ridge.
Snow Density
The mass of snow per unit volume which is equal to the water content of
the snow divided by its depth.
Snow Depth
The combined total depth of both the old and new snow on the ground.
Snow Flurries
Snow flurries are an intermittent light snowfall of short duration
(generally light snow showers) with no measurable accumulation (trace
category).
Snow Grains
Precipitation consisting of white, opaque ice particles usually less than
1 mm in diameter.
Snow Pack
Same as Snowcover; the combined layers of snow and ice on the ground at
any one time.
Snow Pellets
Precipitation, usually of brief duration, consisting of crisp, white,
opaque ice particles, round or conical in shape and about 2 to 5 mm in
diameter. Same as graupel or small hail.
Snow Pillow
1) A window of snow deposited in the immediate lee of a snow fence or
ridge.
or
2) In hydrologic terms, an instrument used to measure snow water
equivalents. Snow pillows typically have flat stainless steel surface
areas. The pillow below this flat surface is filled with antifreeze
solution and the pressure in the pillow is related to the
water-equivalent depth of the snow on the platform. One great advantage
of snow pillows over a snow survey is the frequency of observations,
which can be as high as twice per day.
Snow Shower
A snow shower is a short duration of moderate snowfall. Some accumulation
is possible.
Snow Squall
A snow squall is an intense, but limited duration, period of moderate to
heavy snowfall, accompanied by strong, gusty surface winds and possibly
lightning (generally moderate to heavy snow showers). Snow accumulation
may be significant.
Snow Stake
A 1-3/4 inch square, semi-permanent stake, marked in inch increments to
measure snow depth.
Snow Stick
A portable rod used to measure snow depth.
Snow Water Equivalent
The water content obtained from melting accumulated snow.
Snowboard
A flat, solid, white material, such as painted plywood, approximately two
feet square, which is laid on the ground, or snow surface by weather
observers to obtain more accurate measurements of snowfall and water
content.
Snowcover
Also known as Snow Pack; the combined layers of snow and ice on the ground
at any one time.
Snowflake
An agglomeration of snow crystals falling as a unit.
Snowmelt Flooding
In hydrologic terms, flooding caused primarily by the melting of snow.
Snowpack
The total snow and ice on the ground, including both the new snow and the
previous snow and ice which has not melted.
SNR
Signal-to-Noise Ratio
SNW
Snowfall
SNWFL
Snowfall
SOI
Southern Oscillation Index - a numerical index measuring the state of the
Southern Oscillation. The SOI is based on the (atmospheric) pressure
difference between Tahiti and Darwin, Australia. It is highly correlated
with tropical sea surface temperature anomaly indices recorded in Ni�o3.
Soil Moisture
Water contained in the upper part of the soil mantle. This moisture
evaporates from the soil and is the used and transpired by vegetation.
Solar Coordinates
In solar-terrestrial terms, Central Meridian Distance (CMD). The angular
distance in solar longitude measured from the central meridian.
Solar Cycle
In solar-terrestrial terms, the approximately 11-year quasi-periodic
variation in frequency or number of solar active events.
Solar Maximum
In solar-terrestrial terms, the month(s) during the solar cycle when the
12-month mean of monthly average sunspot numbers reaches a maximum.
Solar Minimum
In solar-terrestrial terms, the month(s) during the solar cycle when the
12-month mean of monthly average sunspot numbers reaches a minimum.
Solar Noon
The time of day at which the sun is the highest in the sky. This time
varies through the year due to the change in speed of the earth's orbit
around the sun.
Solar Sector Boundary (SSB)
In solar-terrestrial terms, the apparent solar origin, or base, of the
interplanetary sector boundary marked by the larger-scale polarity
inversion lines.
Solar Wind
The outward flux of solar particles and magnetic fields from the sun.
Typically, solar wind velocities are near 350 km/s.
SOLN
Solution
SOLNS
solutions
Solstice
Either of the two times per year when the sun is at its greatest
angular distance from the celestial equator: about June 21 (the Northern
Hemisphere summer solstice), when the sun reaches its northernmost point
on the celestial sphere, or about December 22 (the Northern Hemisphere
winter solstice), when it reaches its southernmost point.
SOO
Science and Operations Officer
Sounding
A set of data measuring the vertical structure of an atmospheric
parameter (temperature, humidity, pressure, winds, etc.) at a given time.
Southern Oscillation
(SO) - a "see-saw" in surface pressure in the tropical Pacific
characterized by simultaneously opposite sea level pressure anomalies at
Tahiti, in the eastern tropical Pacific and Darwin, on the northwest
coast of Australia. The SO was discovered by Sir Gilbert Walker in the
early 1920's. Walker was among the first meteorologists to use the
statistical techniques to analyze and predict meteorological phenomena.
Later, the three-dimensional east-west circulation related to the SO was
discovered and named the "Walker Circulation". The SO oscillates with a
period of 2-5 years. During one phase, when the sea level pressure is
low at Tahiti and High at Darwin, the El Ni�o occurs. The cold phase of
the SO, called "La Ni�a" by some, is characterized by high pressure in
the eastern equatorial Pacific, low in the west, and by anomalously cold
sea surface temperature (SST) in the central and eastern Pacific. This is
called El Ni�o Southern Oscillation or ENSO.
Southern Oscillation Index
A numerical index measuring the state of the Southern Oscillation. The
SOI is based on the (atmospheric) pressure difference between Tahiti and
Darwin, Australia. It is highly correlated with tropical sea surface
temperature anomaly indices recorded in Ni�o3.
Space Environment Center
(SEC) - This center provides real-time monitoring and forecasting of
solar and geophysical events, conducts research in solar-terrestrial
physics, and develops techniques for forecasting solar and geophysical
disturbances. SEC's parent organization is the National Oceanic and
Atmospheric Administration (NOAA). SEC is one of NOAA's 12 Environmental
Research Laboratories (ERL) and one of NOAA's 9 National Centers for
Environmental Prediction (NCEP). SEC's Space Weather Operations is
jointly operated by NOAA and the U.S. Air Force and is the national and
world warning center for disturbances that can affect people and
equipment working in the space environment.
SPC
Storm Prediction Center
SPCLY
Especially
SPD
1) Speed
2) On a buoy report, ten-minute average wind speed values in m/s.
Spearhead Echo
A radar echo associated with a downburst with a pointed appendage
extending toward the direction of the echo motion. The appendage moves
much faster than the parent echo, which is drawn into the appendage.
During its mature stage, the appendage turns into a major echo and the
parent echo loses its identity.
Special Avalanche Warning
Issued by the National Weather Service when avalanches are imminent or
occurring in the mountains. It is usually issued for a 24 hour period.
Special Fire Weather
Meteorological services uniquely required by user agencies which cannot
be provided at an NWS office during normal working hours. Examples are
on-site support, weather observer training, and participation in user
agency training activities.
Special Marine Warning
(SMW) A warning product issued for potentially hazardous weather
conditions usually of short duration (up to 2 hours) producing sustained
marine thunderstorm winds or associated gusts of 34 knots or greater;
and/or hail 3/4 inch or more in diameter; and/or waterspouts affecting
areas included in a Coastal Waters Forecast, a Nearshore Marine Forecast,
or an Great Lakes Open Lakes Forecast that is not adequately covered by
existing marine warnings. Also used for short duration mesoscale events
such as a strong cold front, gravity wave, squall line, etc., lasting
less than 2 hours and producing winds or gusts of 34 knots or greater.
Special Tropical Disturbance Statement
This statement issued by the National Hurricane Center furnishes
Information on strong and formative non-depression systems. This
statement focuses on the major threat(s) of the disturbance, such as
the potential for torrential rainfall on an island or inland area. The
statement is coordinated with the appropriate forecast office(s).
Specific Gravity
The ratio of the density of any substance to the density of water.
Specific Humidity
In a system of moist air, the ratio of the mass of water vapor to the
total mass of the system.
Specific Yield
In hydrologic terms, the ratio of the water which will drain freely from
the material to the total volume of the aquifer formation. This value
will always be less than the porosity.
Spectral Density
A radar term for the distribution of power by frequency.
Spectral Wave Density
On a buoy report, energy in (meter*meter)/Hz, for each frequency bin
(typically from 0.03 Hz to 0.40 Hz).
Spectral Wave Direction
On a buoy report, mean wave direction, in degrees from true North, for
each frequency bin.
Spectrum Width
This WSR-88D radar product depicts a full 360 degree sweep of spectrum
width data indicating a measure of velocity dispersion within the radar
sample volume. It is available for every elevation angle sampled, it
provides a measure of the variability of the mean radial velocity
estimates due to wind shear, turbulence, and/or the quality of the
velocity samples. It is used to estimate turbulence associated with
boundaries, thunderstorms, and mesocyclones; check the reliability of
the velocity estimates; and locate boundaries (cold front, outflow,
lake breeze, etc.).
Spectrum Width Cross Section
This WSR-88D radar product displays a vertical cross section of spectrum
width on a grid with heights up to 70,000 feet on the vertical axis and
distance up to 124 nm on the horizontal axis. Two end points to create
cross section are radar operator selected along a radial or from one
AZRAN to another AZRAN within 124 nm of the radar that are less than
124 nm apart.
It is used to:
1) Verify features on the Reflectivity Cross Section (RCS) and Velocity
Cross Section (VCS) and to evaluate the quality of the velocity data.
2) Estimate vertical extent of turbulence (aviation use).
Speed Shear
The component of wind shear which is due to a change in wind speed with
height, e.g., southwesterly winds of 20 mph at 10,000 feet increasing to
50 mph at 20,000 feet. Speed shear is an important factor in severe
weather development, especially in the middle and upper levels of the
atmosphere.
SPENES
NESDIS Satellite Precipitation Estimates
Sphere Calibration
Reflectivity calibration of a radar by pointing the dish at a metal
sphere of (theoretically) known reflectivity. The sphere is often
tethered to a balloon.
Spillway
In hydrologic terms, a structure over or through which excess or flood
flows are discharged. If the flow is controlled by gates, it is a
controlled spillway, if the elevation of the spillway crest is the only
control, it is an uncontrolled spillway.
Spillway Crest
In hydrologic terms, the elevation of the highest point of a spillway.
Spin-Up
Slang for a small-scale vortex initiation, such as what may be seen when
a gustnado, landspout, or suction vortex forms.
SPKL
Sprinkle
Split Flow
A flow pattern high in the atmosphere characterized by diverging winds.
Storms moving along in this type of flow pattern usually weaken.
Splitting Storm
A thunderstorm which splits into two storms which follow diverging paths
(a left mover and a right mover). The left mover typically moves faster
than the original storm, the right mover, slower. Of the two, the left
mover is most likely to weaken and dissipate (but on rare occasions can
become a very severe anticyclonic-rotating storm), while the right mover
is the one most likely to reach supercell status.
SPLNS
Southern Plains
Sporadic E
In solar-terrestrial terms, a phenomenon occurring in the E region of the
ionosphere, which significantly affects HF radiowave propagation.
Sporadic E can occur during daytime or nighttime and it varies markedly
with latitude.
SPOTNIL
In solar-terrestrial terms, a spotless disk.
Spotting
Outbreak of secondary fires as firebrands or other burning materials are
carried ahead of the main fire line by winds.
Spray
An ensemble of water droplets torn by the wind from an extensive body of
water, generally from the crests of waves, and carried up into the air in
such quantities that it reduces the horizontal visibility.
SPRD
Spread
Spring
1. The season of the year comprising the transition period from winter to
summer occurring when the sun is approaching the summer solstice. In the
Northern Hemisphere, spring customarily includes the months of March,
April and May.
2. In hydrologic terms, an issue of water from the earth; a natural
fountain; a source of a reservoir of water.
Spring Tide
A tide higher than normal which occurs around the time of the new and
full moon.
SPS
Severe Weather Potential Statement
SQLN
Squall Line
Squall
1. A strong wind characterized by a sudden onset, a duration of the order
of minutes, and then a rather sudden decrease in speed. In U.S.
observational practice, a squall is reported only if a wind speed of 16
knots or higher is sustained for at least two minutes (thereby
distinguishing it from a gust).
2. In nautical use, a severe local storm considered as a whole, that is,
winds and cloud mass and (if any) precipitation, thunder and lightning.
Squall Line
A line of active thunderstorms, either continuous or with breaks,
including contiguous precipitation areas resulting from the existence of
the thunderstorms.
SRF
(Surf Zone Forecast) - A National Weather Service routine or event driven
forecast product geared toward non-boating marine users issued for an
area extending from the area of water between the high tide level on the
beach and the seaward side of the breaking waves.
SRH
Storm-Relative Helicity
SRN
Southern
SS
Sandstorm
SSHS
Saffir/Simpson Hurricane Scale
SST
Sea Surface Temperature
ST
Stratus
St Lawrence Freeze-Up Outlook
A National Weather Service forecast product to keep mariners informed of
the projected freeze-up date of ice the St. Lawrence River.
St. Elmo's Fire
The glow on a masthead produced by an extreme buildup of electrical
charge. Unprotected mariners should immediately move to shelter when this
phenomena occurs. Lightning may strike the mast within five minutes after
it begins to glow.
Stability
The degree of resistance of a layer of air to vertical motion.
Stability Index
The overall stability or instability of a sounding is sometimes
conveniently expressed in the form of a single numerical value. Used alone,
it can be quite misleading, and at times, is apt to be worthless. The
greatest value of an index lies in alerting the forecaster to those
soundings which should be examined more closely.
Stable
An atmospheric state with warm air above cold air which inhibits the
vertical movement of air.
Stable Boundary Layer
The stably-stratified layer that forms at the surface and grows upward,
usually at night or in winter, as heat is extracted from the atmosphere's
base in response to longwave radiative heat loss from the ground. Stable
boundary layers can also form when warm air is advected over a cold
surface or over melting ice.
Stable Core
Post-sunrise, elevated remnant of the temperature inversion that has
built up overnight within a valley.
Staccato Lightning
A Cloud to Ground (CG) lightning discharge which appears as a single
very bright, short-duration stroke, often with considerable branching.
Stage
The level of the water surface of a river or stream above an established
datum at a given location.
Stair Stepping
In hydrologic terms, the process of continually updating river forecasts
for the purpose of incorporating the effects rain that has fallen since
the previous forecast was prepared.
Standard Atmosphere
A hypothetical vertical distribution of atmospheric temperature,
pressure, and density that, by international agreement, is taken to be
representative of the atmosphere for purposes of pressure altimeter
calibrations, aircraft performance calculations, aircraft and missile
design, ballistic tables, etc.
Standard Synoptic Times
The times of 0000, 0600, 1200, and 1800 UTC. Also known as the main
synoptic times.
State Forecast Product
This National Weather Service product is intended to give a good general
picture of what weather may be expected in the state during the next 5
days. The first 2 days of the forecast is much more specific than the
last 3 days. In comparison with the Zone Forecast Product, this product
will be much more general.
State Weather Roundup
This is a National Weather Service tabular product which provides
routine hourly observations within the state through the National Weather
Wire Service (NWWS). It gives the current weather condition in one word
(cloudy, rain, snow, fog, etc.), the temperature and dew point in
Fahrenheit, the relative humidity, wind speed and direction, and finally
additional information (wind chill, heat index, a secondary weather
condition). These reports are broken up regionally. When the
complementary satellite product is not available, reports from
unaugmented ASOS stations will report "fair" in the sky/weather column
when there are few or no clouds (i.e., scattered or less) below 12,000
feet with no significant weather and/or obstructions to visibility.
Station ID
Five-digit WMO Station Identifier used by the Buoy Data Center since
1976. ID's can be reassigned to future deployments within the same 1
degree square.
Station Model
A specified pattern for plotting, on a weather map, the meteorological
symbols that represent the state of the weather at a particular observing
station.
Station Pressure
The absolute air pressure at a given reporting station. The air pressure
is directly proportional to the combined weight of all air in the
atmosphere located in a column directly above the reporting site.
Consequently, the station pressure may vary tremendously from one
location to another in mountainous regions due to the strong variation of
atmospheric pressure with height. Vertical variations of pressure range
up to 150 mb per mile whereas horizontal variations are usually less than
.1 mb per mile.
Stationary Front
A front between warm and cold air masses that is moving very slowly or not
at all.
STBL
Stable
Steam Fog
Fog formed when water vapor is added to air which is much colder than the
source of the vapor. It may be formed when very cold air drifts across
relatively warm water. At temperatures below about -20�F, ice particles or
droxtals may be formed in the air producing a type of ice fog known as
frost smoke.
Steepness
In marine terms, on a buoy report, wave steepness is the ratio of wave
height to wave length and is an indicator of wave stability. When wave
steepness exceeds a 1/7 ratio, the wave becomes unstable and begins to
break.
Steering Currents
Same as Steering Winds; a prevailing synoptic scale flow which governs
the movement of smaller features embedded within it.
Steering Winds
Same as Steering Currents; A prevailing synoptic scale flow which governs
the movement of smaller features embedded within it.
Stepped Leader
A faint, negatively charged channel that emerges from the base of a
thunderstorm and propagates toward the ground in a series of steps of
about 1 microsecond duration and 50-100 meters in length, initiating a
lightning stroke.
STFR
Stratus Fractus
STG
Strong
Stilling basin
In hydrologic terms, a basin constructed to dissipate the energy of
fast-flowing water (e.g., from a spillway or bottom outlet), and to
protect the streambed from erosion.
STJ
Subtropical Jet - this jet stream is usually found between 20� and 30�
latitude at altitudes between 12 and 14 km.
STLT
Satellite
STM
Stratiform
STNRY
Stationary
Stoplogs
In hydrologic terms, large logs, timbers or steel beams placed on top of
each other with their ends held in guides on each side of a channel or
conduit providing a temporary closure versus a permanent bulkhead gate.
Storm
Any disturbed state of the atmosphere, especially affecting the Earth's
surface, and strongly implying destructive and otherwise unpleasant
weather. Storms range in scale from tornadoes and thunderstorms to
tropical cyclones to synoptic-scale extratropical cyclones.
Storm Data
This National Climatic Data Center (NCDC) monthly publication documents
a chronological listing, by states, of occurrences of storms and unusual
weather phenomena. Reports contain information on storm paths, deaths,
injuries, and property damage. An "Outstanding storms of the month"
section highlights severe weather events with photographs, illustrations,
and narratives. The December issue includes annual tornado, lightning,
flash flood, and tropical cyclone summaries.
Storm Motion
The speed and direction at which a thunderstorm travels.
Storm Relative
Measured relative to a moving thunderstorm, usually referring to winds,
wind shear, or helicity.
Storm Relative Mean Radial Velocity Map
(SRM): This WSR-88D radar product depicts a full 360� sweep of radial
velocity data with the average motion of all identified storms subtracted
out. It is available for every elevation angle sampled. It is used to aid
in displaying shear and rotation in storms and storm top divergence that
might otherwise be obscured by the storm's motion, investigate the 3-D
velocity structure of a storm, and help with determining rotational
features in fast and uniform moving storms.
Storm Relative Mean Radial Velocity Region
(SRR): This WSR-88D radar product depicts a 27 nm by 27 nm region of storm
relative mean radial velocity centered on a point which the operator can
specify anywhere within a 124 nm radius of the radar. The storm motion
subtracted defaults to the motion of the storm closest to the product
center, or can be input by the operator. It is used to examine the
3-dimensional storm relative flow of a specific thunderstorm (radar
operator centers product on a specific thunderstorm; aid in displaying
shear and rotation in thunderstorms and storm top divergence that might
otherwise be obscured by storm motion; and gain higher resolution
velocity product.
Storm Scale
Referring to weather systems with sizes on the order of individual
thunderstorms. See synoptic scale and mesoscale.
Storm Surge
An abnormal rise in sea level accompanying a hurricane or other intense
storm, whose height is the difference between the observed level of the
sea surface and the level that would have occurred in the absence of the
cyclone. Storm surge is usually estimated by subtracting the normal or
astronomic tide from the observed storm tide.
Storm Tide
The actual level of sea water resulting from the astronomic tide combined
with the storm surge. Most NWS flood statements, watches, or warnings
quantifying above-normal tides will report the Storm Tide.
Storm Total Precipitation
This radar image is an estimate of accumulated rainfall since the last
time there was a one-hour, or more, break in precipitation. It is used to
locate flood potential over urban or rural areas, estimate total basin
runoff and provide rainfall accumulations for the duration of the event
and is available only for the short range (out to 124 nm). To determine
accumulated precipitation at greater distances you should link to an
adjacent radar.
Storm Tracking Information
This WSR-88D radar product displays the previous, current, and projected
locations of storm centroids (forecast and past positions are limited to
one hour or less). Forecast tracks are based upon linear extrapolation of
past storm centroid positions, and they are intended for application to
individual thunderstorms not lines or clusters. It is used to provide
storm movement: low track variance and/or 2 or more plotted past positions
signify reliable thunderstorm movement.
Storm Warning
A warning of sustained surface winds, or frequent gusts, in the range of
48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or
occurring, and not directly associated with a tropical cyclone.
Stormwater Discharge
In hydrologic terms, precipitation that does not infiltrate into the
ground or evaporate due to impervious land surfaces but instead flows
onto adjacent land or water areas and is routed into drain/sewer systems.
Straight-Line Hodograph
The name pretty well describes what it looks like on the hodograph. What
causes this shape is a steady increase of winds with height (vertical
wind shear). This shape of hodograph favors multicell thunderstorms.
Straight-line Winds
Generally, any wind that is not associated with rotation, used mainly to
differentiate them from tornadic winds.
Stratiform
Having extensive horizontal development, as opposed to the more vertical
development characteristic of convection. Stratiform clouds cover large
areas but show relatively little vertical development. Stratiform
precipitation, in general, is relatively continuous and uniform in
intensity (i.e., steady rain versus rain showers).
Stratiform Rings and Bands
These occur between the active convective bands of a hurricane outside of
the eye wall. Inner stratiform bands often exhibit the bright band aloft,
a VIP Level 2, and in the lower layers typically show a VIP Level 1.
Stratocumulus
Low-level clouds, existing in a relatively flat layer but having
individual elements. Elements often are arranged in rows, bands, or
waves. Stratocumulus often reveals the depth of the moist air at low
levels, while the speed of the cloud elements can reveal the strength of
the low-level jet.
Stratopause
The boundary between the stratosphere and mesosphere.
Stratosphere
The region of the atmosphere extending from the top of the troposphere to
the base of the mesosphere, an important area for monitoring stratospheric
ozone.
Stratospheric Ozone
In the stratosphere, ozone has beneficial properties where it forms an
ozone shield that prevents dangerous radiation from reaching the Earth's
surface. Recently, it was discovered that in certain parts of the world,
especially over the poles, stratospheric ozone was disappearing creating
an ozone hole.
Stratus
A low, generally gray cloud layer with a fairly uniform base. Stratus may
appear in the form of ragged patches, but otherwise does not exhibit
individual cloud elements as do cumulus and stratocumulus clouds. Fog
usually is a surface-based form of stratus.
Stream line
Arrows on a weather chart showing wind speed and direction. The head of
the arrow points toward where the wind is blowing and the length of the
arrow is proportional to the wind speed. Sometimes shows wind direction
and trajectory only.
Streamflow
In hydrologic terms, water flowing in the stream channel. It is often
used interchangeably with discharge.
STRFM
Stratiform
Striations
Grooves or channels in cloud formations, arranged parallel to the flow
of air and therefore depicting the airflow relative to the parent cloud.
Striations often reveal the presence of rotation, as in the barber pole
or "corkscrew" effect often observed with the rotating updraft of a Low
Precipitation (LP) storm.
Strike
For any particular location, a hurricane strike occurs if that location
passes within the hurricane's strike circle, a circle of 125 n mi
diameter, centered 12.5 n mi to the right of the hurricane center
(looking in the direction of motion). This circle is meant to depict the
typical extent of hurricane force winds, which are approximately 75 n mi
to the right of the center and 50 n mi to the left.
Sub-synoptic Low
Essentially the same as mesolow.
Sublimation
The transition of a substance from the solid phase directly to the vapor
phase, or vice versa, without passing through an intermediate liquid
phase. Thus an ice crystal or icicle sublimes under low relative humidity
at temperatures below 0�C. The process is analogous to evaporation of a
liquid.
Sublimation of ice
The transition of water from solid to gas without passing through the
liquid phase.
Subrefraction
The bending of the radar beam in the vertical which is less than under
standard refractive conditions. This causes the beam to be higher than
indicated, and lead to the underestimation of cloud heights.
Subsidence
1. A descending motion of air in the atmosphere occurring over a rather
broad area.
2. In hydrologic terms, sinking down of part of the earth's crust due to
underground excavation, such as the removal of groundwater.
Subsidence Inversion
A temperature inversion that develops aloft as a result of air gradually
sinking over a wide area and being warmed by adiabatic compression,
usually associated with subtropical high pressure areas.
Substation
A location where observations are taken or other services are furnished
by people not located at NWS offices who do not need to be certified to
take observations.
Subsurface Storm Flow
In hydrologic terms, the lateral motion of water through the upper layers
until it enters a stream channel. This usually takes longer to reach
stream channels than runoff. This also called interflow.
Subtle Heavy Rainfall Signature
This heavy rain signature is often difficult to detect on satellite. These
warm top thunderstorms are often embedded in a synoptic-scale cyclonic
circulation. Normally, they occur when the 500 mb cyclonic circulation is
quasi-stationary or moves slowly to the east or northeast (about 2 degrees
per 12 hours). The average surface temperature is 68�F with northeasterly
winds. The average precipitable water (P) value is equal to or greater
than 1.34 inches and the winds veer with height, but they are relatively
light. The heavy rain often occurs north and east of the vorticity maximum
across the lower portion of the comma head about 2 to 3 degrees north or
northeast of the 850 mb low.
Subtropical Cyclone
A non-frontal low pressure system that has characteristics of both
tropical and extratropical cyclones. This system is typically an
upper-level cold low with circulation extending to the surface layer and
maximum sustained winds generally occurring at a radius of about 100
miles or more from the center. In comparison to tropical cyclones, such
systems have a relatively broad zone of maximum winds that is located
farther from the center, and typically have a less symmetric wind field
and distribution of convection.
Subtropical Depression
A subtropical cyclone in which the maximum 1-minute sustained surface
wind is 33 knots (38 mph) or less.
Subtropical Jet
(Abbrev. STJ) - this jet stream is usually found between 20� and 30�
latitude at altitudes between 12 and 14 km.
Subtropical Storm
A subtropical cyclone in which the maximum 1-minute sustained surface
wind is 34 knots (39 mph) or more.
Suction Vortex
A small but very intense vortex within a tornado circulation. Several
suction vortices typically are present in a multiple-vortex tornado.
Much of the extreme damage associated with violent tornadoes (F4 and F5
on the Fujita scale) is attributed to suction vortices.
Sudden Commencement (SC)
In solar-terrestrial terms, an abrupt increase or decrease in the
northward component of the geomagnetic field, which marks the beginning
of a geomagnetic storm.
Sudden Impulse (SI+ or SI-)
In solar-terrestrial terms, a sudden perturbation of several gammas in
the northward component of the low-latitude geomagnetic field, not
associated with a following geomagnetic storm. (An SI becomes an SC if
a storm follows.)
Sudden Ionospheric Disturbance (SID)
In solar-terrestrial terms, HF propagation anomalies due to ionospheric
changes resulting from solar flares, proton events and geomagnetic storms.
SUF
Sufficient
Summation Principle
This principle states that the sky cover at any level is equal to the
summation of the sky cover of the lowest layer plus the additional sky
cover provided at all successively higher layers up to and including the
layer in question.
Summer
Typically the warmest season of the year during which the sun is most
nearly overhead. In the Northern Hemisphere, summer customarily includes
the months of June, July, and August.
Summer Solstice
The time at which the sun is farthest north in the Northern Hemisphere,
on or around June 21.
Sun Dog
See Parhelion
Sun Pillar
A bright column above or below the sun produced by the reflection of
sunlight from ice crystals.
Sun Pointing
Alignment of the radar antenna by locating the position of the sun in the
sky, which has an exactly known position given the radar's location and
the present time. This may be necessary to verify that when we think
we're pointing "north", we actually are! The sun's signal is usually
several dB above the background noise, and this technique is also
sometimes used to examine the receiver sensitivity.
Sunny
When there are no opaque (not transparent) clouds. Same as Clear.
Sunrise
The phenomenon of the sun's daily appearance on the eastern horizon as
a result of the earth's rotation. The word is often used to refer to
the time at which the first part of the sun becomes visible in the
morning at a given location.
Sunset
The phenomenon of the sun's daily disappearance below the western
horizon as a result of the earth's rotation. The word is often used to
refer to the time at which the last part of the sun disappears below
the horizon in the evening at a given location.
Sunspot
In solar-terrestrial terms, an area seen as a dark spot on the
photosphere of the sun. Sunspots are concentrations of magnetic flux,
typically occurring in bipolar clusters or groups. They appear dark
because they are cooler than the surrounding photosphere.
Sunspot Group Classification
A: A small single unipolar sunspot or very small group of spots without
penumbra.
B: Bipolar sunspot group with no penumbra.
C: An elongated bipolar sunspot group. One sunspot must have penumbra.
D: An elongated bipolar sunspot group with penumbra on both ends of the
group.
E: An elongated bipolar sunspot group with penumbra on both ends.
Longitudinal extent of penumbra exceeds 10 deg. but not 15 deg.
F: An elongated bipolar sunspot group with penumbra on both ends.
Longitudinal extent of penumbra exceeds 15 deg.
H: A unipolar sunspot group with penumbra.
Sunspot Number
In solar-terrestrial terms, a daily index of sunspot activity (R),
defined as R = k (10 g + s) where S = number of individual spots,
g = number of sunspot groups, and k is an observatory factor.
Super Typhoon
Typhoon having maximum sustained winds of 130 knots (150 mph) or greater.
Supercell
Short reference to Supercell Thunderstorm; potentially the most
dangerous of the convective storm types. Storms possessing this
structure have been observed to generate the vast majority of
long-lived strong and violent (F2-F5) tornadoes, as well as downburst
damage and large hail. It is defined as a thunderstorm consisting of
one quasi-steady to rotating updraft which may exist for several hours.
Supercell Thunderstorm
Potentially the most dangerous of the convective storm types. Storms
possessing this structure have been observed to generate the vast
majority of long-lived strong and violent (F2-F5) tornadoes, as well as
downburst damage and large hail. It is defined as a thunderstorm
consisting of one quasi-steady to rotating updraft which may exist for
several hours. Supercells usually move to the right of the mean wind.
These are called "Right Movers" and they are favored with veering winds.
Occasionally, these thunderstorms will move to the left of the mean
wind. These thunderstorms are called "Left Movers". These supercells
typically don't last as long as their "Right Mover" cousins and they
usually only produce large hail (greater than 3/4 inch in diameter) and
severe wind gusts in the excess of 58 miles an hour. Left Movers are
favored when you have backing winds.
Radar will observe essentially one long-lived cell, but small
perturbations to the cell structure may be evident. The stronger the
updraft, the better the chance that the supercell will produce severe
(hail greater than 3/4 inch in diameter, wind gusts greater than 58
miles an hour, and possibly a tornado) weather.
Severe supercell development is most likely in an environment possessing
great buoyancy (CAPE) and large vertical wind shear. A Bulk Richardson
Number of between 15 and 35 favor supercell development. Typically, the
hodograph will look like a horse shoe. This is due to the wind speed
increasing rapidly with height and the wind direction either veering or
backing rapidly with height.
Supercool
To cool a liquid below its freezing point without solidification or
crystallization.
Supercooled Liquid Water
In the atmosphere, liquid water can survive at temperatures colder than
0 degrees Celsius; many vigorous storms contain large amounts of
supercooled liquid water at cold temperatures. Important in the
formation of graupel and hail.
Superrefraction
Bending of the radar beam in the vertical which is greater than
sub-standard refractive conditions. This causes the beam to be lower
than indicated, and often results in extensive ground clutter as well
as an overestimation of cloud top heights.
Surcharge Capacity
In hydrologic terms, the volume of a reservoir between the maximum
water surface elevation for which the dam is designed and the crest of
an uncontrolled spillway, or the normal full-pool elevation of the
reservoir with the crest gates in the normal closed position.
Surf Zone
Area of water between the high tide level on the beach and the seaward
side of the breaking waves.
Surf Zone Forecast
(SRF) - A National Weather Service routine or event driven forecast
product geared toward non-boating marine users issued for an area
extending from the area of water between the high tide level on the
beach and the seaward side of the breaking waves.
Surface Energy Budget
The energy or heat budget at the earth's surface, considered in terms
of the fluxes through a plane at the earth-atmosphere interface. The
energy budget includes radiative, sensible, latent and ground heat
fluxes.
Surface impoundment
In hydrologic terms, an indented area in the land's surface, such as a
pit, pond, or lagoon.
Surface Runoff
In hydrologic terms, the runoff that travels overland to the stream
channel. Rain that falls on the stream channel is often lumped with this
quantity.
Surface Water
Water that flows in streams and rivers and in natural lakes, in
wetlands, and in reservoirs constructed by humans.
Surface Weather Chart
An analyzed synoptic chart of surface weather observations. A surface
chart shows the distribution of sea-level pressure (therefore, the
position of highs, lows, ridges and troughs) and the location and nature
of fronts and air masses. Often added to this are symbols for occurring
weather phenomena. Although the pressure is referred to mean sea level,
all other elements on this chart are presented as they occur at the
surface point of observation.
Surface-based Convection
Convection occurring within a surface-based layer, i.e., a layer in which
the lowest portion is based at or very near the earth's surface. Compare
with elevated convection.
Surge
In solar-terrestrial terms, a jet of material from active regions that
reaches coronal heights and then either fades or returns into the
chromosphere along the trajectory of ascent.
Sustained Overdraft
In hydrologic terms, long-term withdrawal from the aquifer of more water
than is being recharged.
Sustained Wind
Wind speed determined by averaging observed values over a two-minute
period.
SVR
1. Severe
2. Abbreviation for Severe Thunderstorm Warning
SVRL
Several
SW
1. Southwest
2. Snow Showers
SWD
On a buoy report, Swell Direction is the compass direction from which the
swell wave are coming from.
SWE
Snow Water Equivalent (the amount of water content in a snowpack or
snowfall).
SWEAT
Severe Weather ThrEAT index; a stability index developed by the Air Force
which incorporates instability, wind shear, and wind speeds as
follows:
SWEAT=(12 Td 850 ) + (20 [TT-49]) +( 2 f 850) + f 500 + (125 [s+0.2])
where
Td 850 is the dew point temperature at 850 mb,
TT is the total-totals index,
f 850 is the 850-mb wind speed (in knots),
f 500 is the 500-mb wind speed (in knots), and
s is the sine of the angle between the wind directions at 500 mb and 850 mb
(thus representing the directional shear in this layer).
SWEAT values of about 250-300 or more indicate a greater potential for
severe weather, but as with all stability indices, there are no magic
numbers.
The SWEAT index has the advantage (and disadvantage) of using only
mandatory-level data (i.e., 500 mb and 850 mb), but has fallen into
relative disuse with the advent of more detailed upper air sounding
analysis programs.
Swell
Wind-generated waves that have travelled out of their generating area.
Swells characteristically exhibit smoother, more regular and uniform
crests and a longer period than wind waves.
Swell Direction
The direction from which the swells are propagating.
SWH
On a buoy report, swell height is the vertical distance (meters)
between any swell crest and the succeeding swell wave trough.
SWLY
Southwesterly
SWODY1
The Day-1 Convective Outlook, sometimes called the "AC" is a guidance
product issued by the Operational Guidance Branch (OGB) unit of the
Storm Prediction Center (SPC) in Norman, Oklahoma. The Day 1 outlook
outlines areas in the continental United States where severe
thunderstorms may develop during the next 6 to 30 hours.
SWODY2
The Day 2 Convective Outlook is very similar to the Day 1 Outlook. It
is issued only twice a day, at 08Z and 18Z, and covers the period from
12Z the following day to 12Z the day after that. For example, if today
is Monday then the Day 2 Outlook will cover the period 12Z Tuesday to
12Z Wednesday. The outlook issued at 08Z now qualifies the degree of
risk like the Day 1 has (i.e. SLGT, MDT, and HIGH risk areas). The Day 2
Outlook has also includes a general thunderstorm outline.
SWP
On a buoy report, Swell Period is the time (usually measured in seconds)
that it takes successive swell wave crests or troughs pass a fixed point.
SWRN
Southwestern
SWS
Severe Weather Statement
SWWD
Southwestward
SX
Stability Index
SXN
Section
Symmetric Double Eye
A concentrated ring of convection that develops outside the eye wall in
symmetric, mature hurricanes. The ring then propagates inward and leads
to a double-eye. Eventually, the inner eye wall dissipates while the
outer intensifies and moves inward.
Synchronous Detection
Radar processing that retains the received signal amplitude and phase but
that removes the intermediate frequency carrier.
SYNOP
Synoptic - relating to the general weather pattern over a wide region,
such as areas of high and low pressure or frontal boundaries, as opposed
to mesoscale or smaller features such as a thunderstorm.
Synopsis
A broad discussion of the weather pattern expected across any given area,
generally confined to the 0-48 hour time frame.
Synoptic Code
Rules and procedures established by the World Meteorological
Organization (WMO) for encoding weather observations.
Synoptic Scale
The spatial scale of the migratory high and low pressure systems of the
lower troposphere, with wavelengths of 1000 to 2500 km.
Synoptic Track
Weather reconnaissance mission flown to provide vital meteorological
information in data sparse ocean areas as a supplement to existing
surface, radar, and satellite data. Synoptic flights better define the
upper atmosphere and aid in the prediction of tropical cyclone
development and movement.
Synoptic Weather
Weather occurring over a wide region on time scales exceeding 12 hours.
SYNS
Synopsis
SYS
System
Syzygy
In solar-terrestrial terms, the instance (new moon or full moon) when
the earth, sun, and moon are all in a straight line.
--- SBBSecho 3.07-Win32
* Origin: RadioWxNet: The Thunderbolt BBS tbolt.synchro.net (801:1/2)
� Synchronet � Temple of Doom BBS - tod.eothnet.com
