*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
"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
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.
Warning - A product issued by NWS local offices indicating
that a particular weather hazard is either imminent or has been
reported. A warning indicates the need to take action to protect
life and property. The type of hazard is reflected in the type of
warning (e.g., tornado warning, blizzard warning). See short-fuse
Watch - An NWS product indicating that a particular hazard is
possible, i.e., that conditions are more favorable than usual for
its occurrence. A watch is a recommendation for planning,
preparation, and increased awareness (i.e., to be alert for changing
weather, listen for further information, and think about what to do
if the danger materializes).
Watch Box (or Box) - [Slang], a severe thunderstorm or
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
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.
Wedge (or Wedge Tornado) - [Slang], 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.
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 (see Fig. 2). 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.
Wet Microburst - A microburst accompanied by heavy
precipitation at the surface. A rain foot may be a visible sign of a
wet microburst. See dry microburst.
Wind Shear - See shear.
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.
WSR-57, WSR-74 - NWS Weather Surveillance Radar units, replaced
by WSR-88D units.
WSR-88D - Weather Surveillance Radar - 1988 Doppler; NEXRAD