Subj : Wx Terms (W)(1)
To : All
From : Daryl Stout
Date : Sat Jun 24 2017 12:06 am
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.
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