Glossary of NWS Terms, Contractions, Abbreviations, and Acronyms

Advection -- Horizontal transport.

Advisory (ADVY) -- A NWS product that means a weather event may threaten life or property if caution is not exercised.

Anticyclonic -- Clockwise rotation.

ATTM -- At This TiMe.

AVN (AViatioN) -- A short to medium range computer weather prediction model run twice daily in Washington, DC and used by meteorologists to forecast the weather.

Breezy -- Sustained wind speeds of 15-25 mph.

Chance (CHC) -- A 25-55% probability that one point in a forecast area will have precipitation.

CWA,CWFA (County Warning/Forecast Area) -- The area of responsibility of a NWS office.

Cyclonic -- Counter-clockwise rotation.

Dm (dam) -- Decameter.

ETA (as in the Greek letter) -- A short range computer weather prediction model run twice daily in Washington, DC and used by meteorologists to forecast the weather.

FAN -- AVN forecast output (such as high/low temperatures and precipitation) for a specific location; used by meteorologists as a "first guess".

Flash Flood -- A dangerous rise in water level of a creek, stream, or river in a few hours or less, caused by heavy rain, ice jam break-up, earthquake, or dam failure.

Flood -- A rise in water level of a creek, stream, or river that results in water overflowing into the surrounding basin; usually caused by heavy rain, snowmelt, or a combination of the two.

Funnel Cloud -- A visibly rotating column of air extending from the base of a cloud but not touching the ground.

H5 (5H) -- 500 mb pressure surface (geopotential Height); about 18,000 feet above sea level.

"High Clouds" -- Clouds above 20,000 feet; usually cirriform (cirrus).

High Wind -- Sustained winds of 40 mph or higher, or gusts greater than 57 mph (not due to thunderstorms), that are expected to last for an extended period of time.

Inversion -- Temperature increasing with height.

Isolated (ISOLD, ISLD) -- Showers or thunderstorms with 1-25% areal coverage.

Likely -- A 55-75% probability that one point in a forecast area will have precipitation.

"Low Clouds" -- Clouds below 1,000 feet; usually stratiform (stratus).

mb (millibar) -- A unit of pressure.

MRF (Medium Range Forecast) -- A medium range computer weather prediction model run once a day in Washington, DC and used by meteorologists to forecast the weather.

Microburst -- A small downburst from a thunderstorm with horizontal outflow winds extending 2.5 miles or less. Wind speeds of 50 to 100 mph or greater are possible. Microbursts in Northern Arizona are usually associated with high based (dry) thunderstorms.

MOS (Model Output Statistics) -- NGM forecast output (such as temperatures, winds, and precipitation) for a specific location; used by meteorologists as a "first guess".

MSL -- Mean Sea Level.

MSO (Meso Eta) -- A higher resolution version of the Eta computer weather prediction model.

NGM (Nested Grid Model) -- A short range computer weather prediction model run twice daily in Washington, DC and used by meteorologists to forecast the weather.

Numerous -- Showers or thunderstorms with 55-75% areal coverage.

NVA (AVA) -- Negative Vorticity Advection (Anticyclonic Vorticity Advection).

NWS -- National Weather Service.

POP -- Probability Of Precipitation.

PVA (CVA) -- Positive Vorticity Advection (Cyclonic Vorticity Advection).

QPF -- Quantitative Precipitation Forecast.

RH -- Relative Humidity.

Scattered (SCT) -- Showers or thunderstorms with 25-55% areal coverage.

Severe Thunderstorm (SVR TS) -- A thunderstorm which produces winds greater than 57 mph or hail three quarters (3/4) of an inch in diameter or larger.

SFC -- SurFaCe.

Shower (SH) -- Intermittent rain or snow.

Slight Chance (SLGT CHC) -- A 1-25% probability that one point in a forecast area will have precipitation.

Thickness (THKN) -- Height difference between two pressure surfaces; corresponds to the temperature in that layer of the atmosphere.

Tornado -- A violently rotating column of air that is in contact with the ground. Tornadoes usually develop from severe thunderstorms and can produce winds of 100 to 300 mph.

Vorticity (VORT) -- A quantitative measure of "spin" in the atmosphere.

Warning -- A NWS product that means a weather event is occurring or imminent that threatens life or property. Take action immediately.

Watch (WTCH) -- A NWS product that means conditions are favorable for severe weather or dangerous events to occur. Be alert, monitor NOAA Weather Radio or other weather information sources, and be prepared to take action if the watch is upgraded to a warning.

Wind Chill Index (WCI) -- A combined effect of wind and cold temperatures; how cold it "feels" to exposed skin. Values below -20 degrees Farenheit are classified as "Extreme" and can freeze skin in minutes.

Windy -- Sustained wind speeds of 20-30 mph.

Z (Zulu Time) -- Greenwich Mean Time (GMT) , Universal Coordinated Time (UTC).

Zone (ZN) -- A local geographic region of a NWS office's forecast area.

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National Weather Service
Flagstaff Weather Forecast Office
P.O. Box 16057
Bellemont, AZ 86015-6057
http://weather.gov/flagstaff

Tel: (928) 556-9161