Subj : Wx Terms (S)(3)
To   : All
From : Daryl Stout
Date : Thu Jul 20 2017 12:05 am

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.



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