Subj : Weather Glossary (W)
To : All
From : Daryl Stout
Date : Tue Sep 24 2019 12:02 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.
***
W
West
WAA
Warm Air Advection - the advection (movement) of warm air into a region.
Wake
The region of turbulence immediately to the rear of a solid body caused
by the flow of air over or around the body.
Wall Cloud
A localized, persistent, often abrupt lowering from a rain-free base.
Wall clouds can range from a fraction of a mile up to nearly five miles
in diameter, and normally are found on the south or southwest (inflow)
side of the thunderstorm. When seen from within several miles, many wall
clouds exhibit rapid upward motion and cyclonic rotation.
However, not all wall clouds rotate. Rotating wall clouds usually develop
before strong or violent tornadoes, by anywhere from a few minutes up to
nearly an hour. Wall clouds should be monitored visually for signs of
persistent, sustained rotation and/or rapid vertical motion.
"Wall cloud" also is used occasionally in tropical meteorology to
describe the inner cloud wall surrounding the eye of a tropical cyclone,
but the proper term for this feature is eyewall.
Warm Advection
Transport of warm air into an area by horizontal winds. Low-level warm
advection sometimes is referred to (erroneously) as overrunning. Although
the two terms are not properly interchangeable, both imply the presence of
lifting in low levels.
Warm Core Low
A low pressure area which is warmer at its center than at its periphery.
Tropical cyclones exhibit this temperature pattern. Unlike cold core
lows, these lows produce much of their cloud cover and precipitation
during the nighttime.
Warm Front
A transition zone between a mass of warm air and the colder air it is
replacing.
Warm Occlusion
A frontal zone formed when a cold front overtakes a warm front and,
finding colder air ahead of the warm front, leaves the ground and rises
up and over this denser air. Compare with cold occlusion.
Warm Sector
A region of warm surface air between a cold front and a warm front.
Warning
A warning is issued when a hazardous weather or hydrologic event is
occurring, is imminent, or has a very high probability of occurring. A
warning is used for conditions posing a threat to life or property.
Wasatch Wind
A strong easterly wind blowing out of the mouths of the canyons of the
Wasatch Mountains onto the plains of Utah. Also called canyon wind.
Watch
A watch is used when the risk of a hazardous weather or hydrologic event
has increased significantly, but its occurrence, location, and/or timing
is still uncertain. It is intended to provide enough lead time so that
those who need to set their plans in motion can do so.
Watch Box
(or simply "Box") - slang for a Severe Thunderstorm Watch or Tornado Watch
issued by the SPC.
Watch Cancellation
This product will be issued to let the public know when either a Tornado
Watch or Severe Thunderstorm Watch has been canceled early. It is issued
by the Storm Prediction Center (SPC) in Norman, Oklahoma. In the text of
the statement it will specify the severe weather watch number and the
area which the watch covered.
Watch Redefining Statement
This product tells the public which counties/parishes are included in the
watch. This is done not only by writing them all out, but by using the
county FIPS codes in the Header of the product. It is issued by the local
National Weather Service Forecast Office (WFO).
Watch Status Reports
This product lets the NWFO know of the status of the current severe
weather watch (Tornado or Severe Thunderstorm). During the severe weather
watch, the Storm Prediction Center (SPC) will issue these reports
periodically. These reports will describe, in plain language, the current
evaluation of the severe weather situation and whether the watch will
expire or be reissued. A status report is not issued if a cancellation or
replacement has been issued at least 1 hour prior to the expiration time
of the original watch.
Water Equivalent
The liquid content of solid precipitation that has accumulated on the
ground (snow depth). The accumulation may consist of snow, ice formed by
freezing precipitation, freezing liquid precipitation, or ice formed by
the refreezing of melted snow.
Water Pollution
The alteration of the constituents of a body of water by man to such a
degree that the water loses its value as a natural resource.
Water Supply Outlook
A seasonal volume forecast, generally for a period centered around the
time of spring snowmelt (e.g., April-July). The outlooks are in units of
acre-feet and represent the expected volume of water to pass by a given
point during a snowmelt season. The outlook categories include Most
Probable, Reasonable Maximum, and Reasonable Minimum.
Water Table
The level below the earth's surface at which the ground becomes saturated
with water. The water table is set where hydrostatic pressure equals
atmospheric pressure.
Water Vapor Plume
This appears in the water vapor satellite imagery. It is a plume-like
object that extends from the Intertropical Convergence Zone (ITCZ)
northward or southward into the higher latitudes. It is usually located
over a 850 to 700 mb theta-e ridge axis. As a result, it is a favored
location for the development of a Mesoscale Convective Complex (MCC).
Researchers have found it to be a favored region for very heavy rain.
It is thought that the ice crystals located in this plume help
thunderstorms to become highly efficient rainfall producers. In North
America, this is sometimes called the "Mexican Connection".
Water Year
The time period from October 1 through September 30.
Watercourse
Any surface flow such as a river, stream, tributary.
Watershed
Land area from which water drains toward a common watercourse in a
natural basin.
Waterspout
In general, a tornado occurring over water. Specifically, it normally
refers to a small, relatively weak rotating column of air over water
beneath a Cb or towering cumulus cloud. Waterspouts are most common over
tropical or subtropical waters.
The exact definition of waterspout is debatable. In most cases the term
is reserved for small vortices over water that are not associated with
storm-scale rotation (i.e., they are the water-based equivalent of
landspouts). But there is sufficient justification for calling virtually
any rotating column of air a waterspout if it is in contact with a water
surface.
Watt
Unit of power in the MKS system of units; energy per unit of time, one
Joule per second (1 J/s). Abbreviated W.
Wave Crest
The highest part of a wave.
Wave Height
Distance from wave trough to wave crest.
Wave Period
Time, in seconds, between the passage of consecutive wave crests past a
fixed point.
Wave Spectrum
The distribution of wave energy with respect to wave frequency or period.
Wave spectra assist in differentiating between wind waves and swell.
Wave Steepness
The ratio of wave height to wavelength and is an indicator of wave
stability. When wave steepness exceeds a 1/7 ratio; the wave typically
becomes unstable and begins to break.
Wave Trough
The lowest part of the wave.
Wavelength
Distance between crests or troughs of a wave.
WAVEWATCH III
One of the operational forecast models run at NCEP. The WWIII is run four
times daily, with forecast output out to 126 hours.
WBND
Westbound
WBZ
Wet Bulb Zero - the height where the wet-bulb temperature goes below 0�C.
It is important because WBZ heights between 7000 ft and 10,500 ft (above
ground level) correlate well with large hail at the surface when storms
develop in an airmass primed for strong convection. Higher values infer
mid and upper level stability and also indicate a large melting area for
falling hail. Lower WBZ heights indicate that the low level atmosphere
is often too cool and stable to support large hail.
WC/ATWC
West Coast and Alaska Tsunami Warning Center. The National Weather
Service's West Coast and Alaska Tsunami Warning Center in Palmer, AK has
a regional tsunami responsibility for the Canadian coastal regions and
the ocean coasts of all U.S. States except Hawaii. See also PTWC.
WCM
Warning Coordination Meteorologist
WDIR
On a buoy report, wind direction (the direction the wind is coming from
in degrees clockwise from true N) during the same period used for WSPD.
WDLY
Widely
WDSPRD
Widespread
Weak Echo Region
(Abbrev. WER) - A WSR-88D radar product which displays reflectivity for
up to 8 elevation angles for a radar operator selected location as a set
presentation of a storm. The plains in this product are presented in an
ascending order, lowest plain is lowest elevation angle selected. It is
used to depict storm tilt and to identify Weak Echo Regions (WER) and
Bounded Weak Echo Regions (BWER) in thunderstorms.
Weather
The state of the atmosphere with respect to wind, temperature,
cloudiness, moisture, pressure, etc. Weather refers to these conditions
at a given point in time (e.g., today's high temperature), whereas
Climate refers to the "average" weather conditions for an area over a
long period of time (e.g., the average high temperature for today's date).
Weather Forecast Office
(Abbrev. WFO) - this type of National Weather Service office is
responsible for issuing advisories, warnings, statements, and short term
forecasts for its county warning area.
Weatherfax
See RADIOFACSIMILE
Wedge Tornado
Slang for a large tornado with a condensation funnel that is at least as
wide (horizontally) at the ground as it is tall (vertically) from the
ground to cloud base. The term "wedge" often is used somewhat loosely to
describe any large tornado. However, not every large tornado is a wedge.
A true wedge tornado, with a funnel at least as wide at the ground as it
is tall, is very rare.
Wedges often appear with violent tornadoes (F4 or F5 on the Fujita Scale),
but many documented wedges have been rated lower. And some violent
tornadoes may not appear as wedges (e.g., Xenia, OH on 3 April 1974,
which was rated F5 but appeared only as a series of suction vortices
without a central condensation funnel). Whether or not a tornado achieves
"wedge" status depends on several factors other than intensity - in
particular, the height of the environmental cloud base and the
availability of moisture below cloud base. Therefore, spotters should not
estimate wind speeds or F-scale ratings based on visual appearance alone.
However, it generally is safe to assume that most (if not all) wedges have
the potential to produce strong (F2/F3) or violent (F4/F5) damage.
WEFAX
System for transmitting weather charts and imagery via satellite.
Occasionally used as an abbreviation for radiofacsimile via HF radio.
Weighing-Type Precipitation Gage
A rain gage that weighs the rain or snow which falls into a bucket set on
a platform of a spring or lever balance. The increasing weight of its
contents plus the bucket are recorded on a chart. The record thus shows
the accumulation of precipitation.
Weir
In hydrologic terms,
(a) A low dam built across a stream to raise the upstream water level
(fixed-crest weir when uncontrolled);
(b) A structure built across a stream or channel for the purpose of
measuring flow (measuring or gaging weir).
WER
Weak Echo Region - Radar term for a region of relatively weak reflectivity
at low levels on the inflow side of a thunderstorm echo, topped by
stronger reflectivity in the form of an echo overhang directly above it.
The WER is a sign of a strong updraft on the inflow side of a storm,
within which precipitation is held aloft. When the area of low
reflectivity extends upward into, and is surrounded by, the higher
reflectivity aloft, it becomes a BWER.
West African Disturbance Line
A line of convection about 300 miles long, similar to a squall line. It
forms over west Africa north of the equator and south of 15 degrees
North latitude. It moves faster than an Easterly Wave between 20 and 40
mph. They move off the African coast every 4 to 5 days mainly in the
summer. Some reach the American tropics and a few develop into tropical
cyclones.
West Wall
The coast side boundary of the Gulf Stream, typically south of Cape
Hatteras. See also North Wall.
Westerlies
The prevailing winds that blow from the west in the mid-latitudes.
Wet Bulb Zero
(Abbrev. WBZ) - the height where the wet-bulb temperature goes below 0�C.
It is important because WBZ heights between 7000 ft and 10,500 ft (above
ground level) correlate well with large hail at the surface when storms
develop in an airmass primed for strong convection. Higher values infer
mid and upper level stability and also indicate a large melting area for
falling hail. Lower WBZ heights indicate that the low level atmosphere is
often too cool and stable to support large hail.
Wet Floodproofing
In hydrologic terms, an approach to floodproofing which usually is a last
resort. Flood waters are intentionally allowed into the building to
minimize water pressure on the structure. Wet Floodproofing can include
moving a few valueable items to a higher place or completely rebuilding
the floodable area. Wet floodproofing has an advantage over other
approaches: no matter how little is done, flood damage will be reduced.
Thousands of dollars in damage can be avoided just by moving furniture and
appliances out of the flood-prone area.
Wet Microburst
A microburst accompanied by heavy precipitation at the surface. A rain
foot may be a visible sign of a wet microburst.
Wet-Bulb Temperature
The lowest temperature that can be obtained by evaporting water into the
air.
Wetland
In hydrologic terms, an area that is regularly wet or flooded and has a
water table that stands at or above the land surface for at least part of
the year.
WFO
Weather Forecast Office - this type of National Weather Service office is
responsible for issuing advisories, warnings, statements, and short term
forecasts for its county warning area.
WFP
Warm Front Passage
Whirlwind
A small, rotating column of air; may be visible as a dust devil.
White Light (WL)
Sunlight integrated over the visible portion of the spectrum (4000 to
7000 angstroms) so that all colors are blended to appear white to the
eye.
White Light Flare
In solar-terrestrial terms, a major flare in which small parts become
visible in white light. Such flares are usually strong X-ray, radio, and
particle emitters.
Whitecap
The breaking crest of a wave, usually white and frothy.
Widespread
Areal coverage of non-measurable, non-convective weather and/or
restrictions to visibility affecting more than 50 percent of a forecast
zone(s).
Wildfire
Any free burning uncontainable wildland fire not prescribed for the area
which consumes the natural fuels and spreads in response to its
environment.
Wildlands
Any nonurbanized land not under extensive agricultural cultivation,
e.g., forests, grasslands, rangelands.
Willy-Willy
A tropical cyclone of hurricane strength near Australia.
Wind
The horizontal motion of the air past a given point. Winds begin with
differences in air pressures. Pressure that's higher at one place than
another sets up a force pushing from the high toward the low pressure.
The greater the difference in pressures, the stronger the force. The
distance between the area of high pressure and the area of low pressure
also determines how fast the moving air is accelerated. Meteorologists
refer to the force that starts the wind flowing as the "pressure
gradient force." High and low pressure are relative. There's no set
number that divides high and low pressure. Wind is used to describe the
prevailing direction from which the wind is blowing with the speed given
usually in miles per hour or knots.
Wind Advisory
Sustained winds 25 to 39 mph and/or gusts to 57 mph. Issuance is normally
site specific. However, winds of this magnitude occurring over an area
that frequently experiences such winds.
Wind Chill
Reference to the Wind Chill Factor; increased wind speeds accelerate heat
loss from exposed skin, and the wind chill is a measure of this effect.
No specific rules exist for determining when wind chill becomes
dangerous. As a general rule, the threshold for potentially dangerous
wind chill conditions is about -20�F.
Wind Chill Advisory
The National Weather Service issues this product when the wind chill could
be life threatening if action is not taken. The criteria for this warning
varies from state to state.
Wind Chill Factor
Increased wind speeds accelerate heat loss from exposed skin. No specific
rules exist for determining when wind chill becomes dangerous. As a
general rule, the threshold for potentially dangerous wind chill
conditions is about -20�F.
Wind Chill Warning
The National Weather Service issues this product when the wind chill is
life threatening. The criteria for this warning varies from state to state.
Wind Couplet
An area on the radar display where two maximum wind speeds are blowing in
opposite directions.
Wind Direction
The true direction from which the wind is blowing at a given location
(i.e., wind blowing from the north to the south is a north wind). It is
normally measured in tens of degrees from 10 degrees clockwise through
360 degrees. North is 360 degrees. A wind direction of 0 degrees is only
used when wind is calm.
Wind Field
The three-dimensional spatial pattern of winds.
Wind Gust
Rapid fluctuations in the wind speed with a variation of 10 knots or more
between peaks and lulls. The speed of the gust will be the maximum
instantaneous wind speed.
Wind Radii
Term used in National Weather Tropical Cyclone Forecast Advisory products
(TCM). Wind radii are the largest radii of that wind speed found in that
quadrant. Quadrants are defined as NE (0-90), SE (90-180), SW (180-270),
and NW (270-0). As an example, given maximum 34 knot radii to 150 nm at
0 degrees, 90 at 120 degrees, and 40 nm at 260 degrees, the following line
would be carried in the forecast/advisory: 150NE 90SE 40SW 150NW.
Wind Rose
A diagram, for a given locality or area, showing the frequency and strength
of the wind from various directions.
Wind Shear
The rate at which wind velocity changes from point to point in a given
direction (as, vertically). The shear can be speed shear (where speed
changes between the two points, but not direction), direction shear (where
direction changes between the two points, but not speed) or a combination
of the two.
Wind Shear Profile
The change in wind speed and/or direction usually in the vertical. The
characteristics of the wind shear profile are of critical importance in
determining the potential for and type of severe weather.
Wind Shift
A change in wind direction of 45 degrees or more in less than 15 minutes
with sustained wind speeds of 10 knots or more throughout the wind shift.
Wind Shift Line
A long, but narrow axis across which the winds change direction (usually
veer).
Wind Sock
A tapered fabric shaped like a cone that indicates wind direction by
pointing away from the wind. It is also called a "wind cone."
Wind Speed
The rate at which air is moving horizontally past a given point. It may be
a 2-minute average speed (reported as wind speed) or an instantaneous
speed (reported as a peak wind speed, wind gust, or squall).
Wind Waves
Local, short period waves generated from the action of wind on the water
surface (as opposed to swell). Commonly referred to as waves. In a
National Weather Service Coastal Marine Forecast or Offshore Forecast,
wind waves are used when swells are described in the forecast.
or
Waves generated by the local wind blowing at the time of observation.
Windward
The side toward the wind. Compare with leeward.
Windy
20 to 30 mph winds.
WINT
winter
Winter
Typically the coldest season of the year during which the sun is farthest
from overhead. In the Northern Hemisphere, winter customarily includes the
months of December, January and February.
Winter Pool
The pool, or height of the water surface, of a reservoir during the
winter. This pool is usually a specific height and is maintained for the
control of late winter and spring flooding.
Winter Solstice
The time at which the sun is farthest south in the Southern Hemisphere,
on or around December 21.
Winter Storm Warning
This product is issued by the National Weather Service when a winter storm
is producing or is forecast to produce heavy snow or significant ice
accumulations. The criteria for this warning can vary from place to place.
Winter Storm Watch
This product is issued by the National Weather Service when there is a
potential for heavy snow or significant ice accumulations, usually at least
24 to 36 hours in advance. The criteria for this watch can vary from place
to place.
Winter Weather Advisory
This product is issued by the National Weather Service when a low pressure
system produces a combination of winter weather (snow, freezing rain,
sleet, etc.) that present a hazard, but does not meet warning criteria.
Wire Weight Gage
In hydrologic terms, a river gage comprised of a weight which is lowered to
the water level. The weight is attached to a cable; and as the weight is
lowered, a counter indicates the length of cable released. The stage is
determined from the length of cable required to reach the water level.
WK
Weak
WKN
Weaken
WL
Will
WLY
Westerly
WMC
World Meteorological Center(s)
WMO
World Meteorological Organization (UN)
WND
Wind
Wolf Number
A historic term for Sunspot Number. In 1849, R. Wolf of Zurich originated
the general procedure for computing the sunspot number.
Wrapping Gust Front
A gust front which wraps around a mesocyclone, cutting off the inflow of
warm moist air to the mesocyclone circulation and resulting in an occluded
mesocyclone.
WRCC
Western Regional Climate Center
WRM
Warm
WRMFNT
Warm Front
WRN
Western
WRNG
Warning
WSFO
Weather Service Forecast Office
WSHFT
Wind Shift
WSPD
On a buoy report, the wind speed (m/s) averaged over an eight-minute
period for buoys and a two-minute period for land stations. Reported
Hourly.
WSR-57
A NWS Weather Surveillance Radar designed in 1957. It used to be part of
weather radar network. It was replaced by WSR-88D units.
WSR-74
A NWS Weather Surveillance Radar designed in 1974. It used to be part of
weather radar network. It was replaced by WSR-88D units.
WSR-88D
Weather Surveillance Radar - 1988 Doppler; NEXRAD unit.
WSR-88D System
The summation of all hardware, software, facilities, communications,
logistics, staffing, training, operations, and procedures specifically
associated with the collection, processing, analysis, dissemination and
application of data from the WSR-88D unit.
WSW
Winter Storm Message
WTMP
On a buoy report, the sea surface temperature (Celsius).
WTR
Water Equivalent
WV
1. Water Vapor (satellite imagery)
2. Wave
3. West Virginia
WVHT
On a buoy report, significant wave height (meters) is calculated as the
average of the highest one-third of all of the wave heights during the
20-minute sampling period.
WW
Severe Thunderstorm or Tornado Watch
WWH
On a buoy report, Wind Wave Height is the vertical distance (meters)
between any wind wave crest and the succeeding wind wave trough
(independent of swell waves).
WWP
On a buoy report, Wind Wave Period is the time (in seconds) that it takes
successive wind wave crests or troughs to pass a fixed point.
WWV
National Institute of Standards and Technology (NIST) radio stations
which broadcast a time and frequency service commonly known to mariners
as the "Time Tick", used as an aid in celestial navigation. Included in
these are hourly voice broadcasts of current warnings for the Atlantic,
Pacific and Gulf of Mexico provided by the National Weather Service.
WWVH
National Institute of Standards and Technology (NIST) radio stations
which broadcast a time and frequency service commonly known to mariners
as the "Time Tick", used as an aid in celestial navigation. Included in
these are hourly voice broadcasts of current warnings for the Atlantic,
Pacific and Gulf of Mexico provided by the National Weather Service.
