Explanation of Terms Commonly Used in the
West Central Texas Area Forecast Discussion

The West Central Texas Area Forecast Discussion(AFD)) written by National Weather Service San Angelo meteorologists specifically for West Central Texas. The AFD is issued three times daily (by 4 AM, 4 PM and 930 PM) and updated as needed. On September 15, 2005, NWS San Angelo added an Aviation section to the AFD, which is updated four times daily (0530Z, 1130Z, 1730Z 2330Z). For both public and aviation forecasting, the AFD contains the reasoning, or the why behind the forecast.

Meteorology is a technical field and meteorologists sometimes use technical terminology to describe the weather. Although we make an effort to reduce the amount of technical jargon in the AFD, we may still use a word that you do not understand. That is where this web page comes in.

What follows is a mostly non-technical explanation of meteorological terms used in the AFD. Bear in mind that this list is incomplete and will grow over time. If there is a term of which you would like to know the meaning, do not hesitate to email us!

See the Links section below for more complete glossaries of meteorological terms. Note: A more complete and technically-oriented glossary of meteorological terms can be found here.

AFD: Area Forecast Discussion

CAA: (Cold Air Advection) The movement of colder air into a region.

WAA: (Warm Air Advection) The movement of warmer air into a region.

LLJ: (Low Level Jet) a river of fast moving air, usually from the south, 2000 to 6000 feet off the ground.   Usually occurs at night and can cause gusty winds at the surface, especially downwind from a range of hills.

Shortwave Trof: An upper level disturbance usually embedded in the flow aloft. Relatively quick moving. Usually produces unsettled weather.

Longwave Trof: A large dip in the upper level jetstream. Slow moving. Usually produces unsettled weather.

Pacific Front: A cold front of Pacific, or Western United States origin.

Arctic Front: A cold front of Arctic origin, usually northern Canada or Siberia.

CAPE: Convective Available Potential Energy. A measurement of atmospheric instability. High CAPE values often favor severe thunderstorm development.

CINH: Convective Inhibition: The "opposite" of CAPE. A measure of stability in the atmosphere. High CINH typically supresses thunderstorm development.

Models: Computer programs that attempt to "model" or predict the atmosphere's behavior.

GOES: Geostationary Operational Environmental Satellite.

GFS: An atmospheric computer model: Global Forecasting System. GFS40 (40km resolution) runs four times daily and has output to 192 hours. The GFS90 (90km resolution) runs twice daily and has output to 240 hours.

Eta or NAM: An atmospheric computer model that runs four times daily. Output is to 84 hours.

Guidance: Raw computer model-generated temperature, wind, moisture guidance, uncorrected by meteorologists.

MAV: Guidance generated from the GFS computer model - example

MEX: Guidance generated from the GFS computer model - example

MET: Guidance generated from the Eta computer model - example

VAD Wind Profile: Vertical profile of the wind (from 1000 to 50,000 feet) generated by the WSR-88D Doppler Radar.

Sounding: A vertical profile of temperature, dewpoint and wind reported by weather balloons launched twice daily. More frequent, but less accurate GOES satellite-based soundings are also available. Examples can be found on the Current Weather page under "GOES Sounder Products"..

POP or POPs: Probability of Precipitation - the chance that measurable precipitation (0.01 inch or more) will occur within a 12 hour period over any given point in the forecast area.

Veering Wind: The clockwise change in wind direction at a single point over time, or the clockwise change in wind direction upward through a vertical distance

Backing Wind: The counter-clockwise change in wind direction at a single point over time, or the counter-clockwise change in wind direction upward through a vertical distance

Wind Shear: The change in the velocity (direction and/or speed) of wind with height. Wind sheer can affect thunderstorm type and severity. Wind shear, both convective and non-convective, can create turbulence that can affect aircraft in flight.

WC TX: West Central Texas

METAR: An hourly surface observation of temperature, dewpoint, wind, visibility, pressure, precipitation, weather and cloud cover/height. Equipment used to record METARs are typically located at airports.
KSJT / SJT: San Angelo
KABI / ABI: Abilene
KJCT / JCT: Junction
KBWD / BWD: Brownwood
KSWW / SWW: Sweetwater
KBBD / BBD: Brady
KSOA / SOA: Sonora
KMAF / MAF: Midland
KLBB / LBB / LUB: Lubbock
KFWD / FWS / FTW: Fort Worth
METAR Identifier Lookup
See a map with the (3-letter, minus the "K") location codes

Z Time: Example: "18Z". "Z" is shorthand for Zulu Time or GMT (Greenwich Mean Time). Z time/GMT time does not change as one moves around the globe and is thus well suited for the aviation and the marine community. Z time/GMT time is based on the time at the 0 degree longitude, which runs through Greenwich England. To convert Z or GMT time to Central Daylight time, subtract five hours. Example: 18z equals 13 CDT, or 1 pm CDT. Subtract six hours to compute Central Standard Time. For more information: Click here.

Links
Geographical terms used in the AFD and on NOAA Weather Radio
American Meteorological Society Glossary of Meteorology