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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.
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.
A boundary between a warm air mass that is replacing a cooler air mass.
Issued when a particular hazard is "imminent" or already occurring (e.g., tornado warning, flash flood warning).
Forecast issued in advance to alert the public of the possibility of a particular hazard (e.g., tornado watch, flash flood watch).
Watch Box (or Box)
[Slang], a severe thunderstorm or tornado watch.
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.
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.
Weather is the specific condition of the atmosphere at a particular place and time. It is measured in terms of such things as wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather can change from hour-to-hour, day-to-day, and season-to-season. Climate is the average of weather over time and space. A simple way of remembering the difference is that climate is what you expect (e.g. cold winters) and 'weather' is what you get (e.g. a blizzard).
weather watch redefining statement
Issued for every tornado and severe thunderstorm watch that affects a state. It lists the type of watch, its corresponding number, the ending time of the watch, all counties included in the watch, and large cities and towns in the watch area.
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.
A microburst accompanied by heavy precipitation at the surface. A rain foot may be a visible sign of a wet microburst.
Related Term : Dry Microburst
wind advisory (also lake wind advisory)
Wind Advisory issued when sustained winds of 30 mph or greater are expected to last for 1 hour or more, or for gusts of 45 to 57 mph for any duration. Lake Wind Advisory issued for area lakes when sustained winds of 30 mph or more are expected.
The portion of the cooling of the human body caused by air motion. Wind chill becomes important for human health as air motion accelerates the rate of heat loss from a human body, especially when temperatures are below 45oF.
Wind Chill Index
A means of quantifying the threat of heat loss from the human body during windy and cold conditions.
wind chill warning
Issued when wind chill temperatures are expected to reach -10°F or colder, with a minimum wind speed of about 10 mph. (Test criteria for the 2002 / 2003 winter season.)
The change of wind speed or direction with distance or height.
An instrument that determines the direction from which a wind is blowing.
The wind speed and direction in an undisturbed flow.
Used to describe the prevailing direction from which the wind is blowing, with speeds given in miles per hour. The numbers may vary throughout regions due to such variables as terrain and elevation.