Deciphering Meteorology's "Acronym Soup"

The weather forecasting community can never seem to let a good acronym get by. But if any of these stalwarts of brevity have ever stumped you as to their meaning, we have a good guide for figuring them out:

The weather forecasting community can never seem to let a good acronym get by — an obvious fact if you’ve ever tried to read National Weather Service forecast discussions or followed a meteorologist on social media.

But if any of these stalwarts of brevity have ever stumped you as to their meaning, we have a good guide for the decipher:

AFD -- Area Forecast Discussion. A product written by National Weather Service forecasters four times a day giving their thoughts and reasoning behind their latest forecast. 

ASOS -- Automated Surface Observing System. Automated weather instruments used to track current conditions. A list of stations currently active and available through the NWS website can be found here.

CAPE -- Convective Available Potential Energy. A measure of the amount of energy available for convection with higher values signifying the potential for severe weather. Values over 1,000 Joules/kilogram show significant potential with extreme cases reaching over 5,000. (LINK: Current CAPE Forecast chart)

CWA -- County Warning Area -- The region a specific NWS office covers for its forecasts and warnings. 

ECMWF -- European Center for Medium-range Weather Forecasting. A consortium of 34 nations that produce a global forecast model. Also colloquially known as "The European Model" or "The Euro".

ENSO- - "El Nino Southern Oscillation" -- the El Nino/La Nina cycle in the central Pacific Ocean. 

GDPS or GEM -- Global Environmental Multiscale Model -- A global forecast model run by the Canadian Meteorological Centre. Also colloquially known as the "Canadian Model" or CMC or now GDPS for Global Deterministic Prediction System.

GFS -- Global Forecast System - A global forecast model run in the United States by NOAA. Also sometimes colloquially referred to as "The American Model".

hPa — Hectopascal. The metric unit of pressure. One hPa is equal to 1 millibar. Historically, 1000 hPa was deemed as the standard atmospheric pressure at the surface, but modern-day calculations put that number at 1013.25 hPa, which converts to 29.92 inches of mercury for those who have home barometers.

IFR -- Instrument Flight Rules. When weather or visibility is poor and pilots must rely on instruments for navigation.

IR -- Infrared Satellite Imagery. Using infrared sensors that measure temperature allow meteorologists to "see" clouds even at night. Clouds that reach higher into the atmosphere have colder tops and show up in brighter white colors than lower, warmer clouds, allowing meteorologists to gauge storm intensity. 

K Index — A measure of atmospheric instability and thunderstorm potential.

Kp Index (also "Planetary K-Index") -- A 3-hourly planetary geomagnetic index of activity on a scale of 0-10. Geomagnetic storm conditions are generally considered 6 or greater with values of 7 or higher indicating significant solar storm activity, with potential for Northern Lights sightings into the mid-latitudes.

KT or KTS -- Knots. One knot is 1 nautical mile per hour. To convert to traditional mph, 1 knot = 1.15 mph.

LI -- Lifted Index - Another measure of atmospheric instability and thunderstorm potential. Positive values indicate a stable atmosphere. Negative numbers indicate instability with larger negative numbers indicating greater thunderstorm potential. 

MJO -- Madden-Julian Oscillation. A measurement of tropical rainfall in the Pacific Ocean that goes through 30-60 day cycles. "They significantly affect the atmospheric circulation throughout the global Tropics and subtropics, and also strongly affect the wintertime jet stream and atmospheric circulation features over the North Pacific and western North America." As a result, they have an important impact on storminess and temperatures over the United States. During the summer these oscillations have a modulating effect on hurricane activity in both the Pacific and Atlantic basins.

MCC -- Mesoscale Convective Complex. A large Mesoscale Convective System (MCS)

MCS -- Mesoscale Convective System. A complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more.

METAR -- An international code used for reporting, recording and transmitting weather observations.

MOS -- Model Output Statistics. A computerized forecast that uses statistical guidance to match current conditions to past events to help craft its prediction.

MSL -- Mean Sea Level. The arithmetic mean of hourly water elevations observed over a specific 19-year tidal period.

NEXRAD — NEXt Generation RADar. A NWS network of about 140 Doppler radars operating nationwide.

NHC -- National Hurricane Center. NOAA center responsible for tracking hurricanes and tropical systems.

PDO -- Pacific Decadal Oscillation. Measures sea surface temperature anomalies in the North-Central Pacific Ocean and the Gulf of Alaska. These events range on 20-30 year cycles.

PNS -- Public Information Statement. Issued by the National Weather Service for general non-hazardous weather events or public educational vents.

POP -- Probability of Precipitation. Usually given in a percentage. (MORE: Why It Rained When Your Weather App Said There Was Only A 20% Chance of Precipitation)

PWAT -- Precipitable Water. The measure of vapor content in the atmosphere at a given location and can be useful in predicting heavy rain and potential flooding events. The measurement given is the depth of water if all of it was rained out between the ground and about 30,000 feet.

QPF -- Quantitative Precipitation Forecast. What forecast models predict for the amount of precipitation over a specific region and time. "Model output shows high QPF with incoming cold front" would suggest a prediction of heavy rains. A model would give a specific QPF amount such as 0.54" in 6 hours.

RAWS -- Remote Automated Weather System -- A network of weather stations that provide current conditions to the National Weather Service and the general public.

RH -- Relative Humidity. It is a measure in percentage of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature. (MORE: Why the Dew Point is the Best Way to Measure How Humid it Feels)

RUC -- Rapid Update Cycle model. A numerical model run by NOAA, that focuses on short-term forecasts out to 12 hours.

RVR -- Runway Visual Range. Seen on hourly observations at airports, it's defined as the maximum distance at which the runway, or the specified lights or markers delineating it, can be seen from a position above a specified point on its centerline. It's calculated from visibility, ambient light level, and runway light intensity.

SCA -- Small Craft Advisory. Marine warning indicating speeds of 21-33 knots and/or seas of 10 feet or higher are expected in that area and present dangerous conditions for smaller vessels.

SFC -- "Surface". Sometimes abbreviated as such on NWS forecast discussions.

SLP -- Sea Level Pressure. Usually reported in hPa or millibars. Surface observations will convert the actual pressure at their elevation to sea level pressure to get a consistent sense of how the pressure is changing across wide regions and various elevations. 

SPC -- (NOAA's) Storm Prediction Center. Tasked with tracking severe weather outbreaks in the U.S.

SST -- Sea Surface Temperature.

SWE -- Snow Water EquivalentA measurement showing the amount of water that will be released from snowpack when it melts. (MORE: How much snow will an inch of rain produce?

TCU -- Towering Cumulus Clouds -- noted on hourly weather observations and pilot reports. 

TD -- Tropical Depression -- A tropical depression is a tropical cyclone that has maximum sustained surface winds (one-minute average) of 38 mph (33 knots) or less.

TS -- Tropical Storm -- A tropical storm is a tropical cyclone that has maximum sustained surface winds ranging from 39-73 mph (34 to 63 knots).

UKMET -- A medium-range (3 to 7 day) numerical weather prediction model operated by the United Kingdom METeorological Agency. 

UTC -- Universal Time, Coordinated. Global time standard set along the Prime Meridian. The United States ranges from 5-8 hours behind UTC during Standard Time period and 4-7 hours during Daylight Savings Time. (MORE: What Does ‘12Z' Mean?)

VFR -- Visual Flight Rules -- When weather is clear enough that pilots can see where they are going. 

WFO -- Weather Forecast Office -- How National Weather Service Offices refer to themselves.

WRF -- Weather Research Forecast model. A next-generation numerical weather prediction system designed for both atmospheric research and day-to-day forecasting.

ZFP -- Zone Forecast Product - a regular forecast issued by local National Weather Service offices that break down their coverage area into regions.