WAA – Warm Air Advection
WALL CLOUD -An isolated lowering of a cloud that is attached to the rain-free base of a thunderstorm, generally to the rear of the visible precipitation area. Wall clouds indicate the updraft of or the inflow to a thunderstorm.
WARM FRONT – A boundary between a warm airmass that is replacing a cooler airmass.
WARNING – is issued when severe or hazardous weather has already developed and has been reported by spotters or indicated by radar. Warnings are statements of imminent danger and are issued for relatively small areas near and downstream from the severe storm or flood. For example, Tornado Warning, Severe Thunderstorm Warning, Flash Flood Warning, Winter Storm Warning.
WATCH – identifies a relatively large area in which hazardous or severe weather might occur. The watch is only an indication of where and when the severe weather probabilities are the highest, and should not be confused with a warning. Examples include Tornado Watch, Severe Thunderstorm Watch, Flash Flood Watch, Winter Storm Watch.
WATERSPOUT – A violently rotating column of air usually forming a pendant from a cumulus/cumulonimbus cloud, occurring over a body of water, and having circulation reaching the water.
WATER VAPOR – water substance in a gaseous state that comprises one of the most important of all the constituents of the atmosphere.
WCM – Warning Coordination Meteorologist.
WFO – Weather Forecast Office. Designation of NWS operational offices after modernization.
WIND – air in motion relative to the surface of the earth.
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 (e.g., the normal strong summertime winds near the San Francisco Bay, would not require the issuance of this product).
WIND CHILL- The apparent temperature that describes the cooling effect on exposed skin by the combination of temperature and wind, expressed as a loss of body heat. An increase in wind speed or decrease in temperature will accelerate the effect. A wind chill factor of 30 degrees or lower on exposed skin will result in frostbite in a short period of time.
WIND SHEAR -The change of wind speed or direction with distance or height.
WIND VANE– An instrument that determines the direction from which a wind is blowing.
WINDY – Sustained winds of 20 to 30 mph.
WRCC – Western Regional Climate Center, Reno, NV.