Prioritize...
This section is optional! Learning to read coded weather observations is a key skill for aspiring meteorologists and folks who are going to be working with real-time weather observations, so if you are planning on continuing with other meteorology courses in the future, I recommend at least familiarizing yourself with what a METAR observation is, what they look like, and what type of observation data they contain.
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Explore Further...
If you are ever going to be working with real-time weather data (perhaps to see how your forecast is faring), you are going to need to decode METAR observations. For the record, METAR is a French acronym that loosely translates to "aviation routine weather report" and is an internationally coded weather observation at an airport. Because of their coded nature, METARS require a bit of practice to read, but by looking at raw METARS, you can glean much more information than the standard decoded observations show on a station model. For reference, I refer you to Chapter 12 of the Federal Meteorological Handbook (opens in a new window) that serves as the "bible" of encoding METARS.
Okay, let's get right to it and decode the METAR below. While "METAR" loosely translates to "routine aviation weather observation," your may see a report beginning with "SPECI," which translates to a special (unscheduled) report.
METAR KCON 131151Z AUTO 09009KT 1 3/4SM +RA BR OVC010 09/07 A3005 RMK AO2 CIG 007V013 SLP177 P0015 60056 70066 T00890072 10094 20089 53018
KCON is the four-character ICAO (International Civil Aviation Organization (opens in a new window)) identifier for Concord, New Hampshire. You can use the station list (opens in a new window) at the National center for Atmospheric Research to help you decipher any identifier.
131151Z - the observation was taken on the 13th (May, 2006) at 1151Z (you always determine the month and year in the context of real time).
AUTO indicates a fully automated report with no human intervention. If an observer takes or augments observations, this tag does not appear. Sometimes you might see COR, which indicates a corrected observation.
09009KT indicates that the wind blew from 90 degrees (an easterly wind) at 9 knots. What happens if winds are gusty? Let's look at a METAR below from Mount Washington in New Hampshire (see photograph below) at the same time as the first METAR from Concord):
KMWN 131147Z 13043G58KT 1/16SM FZRA PL FZFG VV001 M01/M01 RMK PLB40 VRY LGT GICG 60074 70148 931000 10017 21013
Winds were blowing from 130 degrees sustained at 43 knots and gusting to 58 knots. That's just a ho-hum "breeze" compared to the world-record setting 231 miles an hour (opens in a new window) clocked at the summit on April 12, 1934. Yes, Mount Washington (opens in a new window) is a windy place indeed.
In stark contrast to windy Mount Washington, a METAR entry of 00000KT represents a calm wind. When the wind is light (a speed of six knots or less) and it varies in direction with time, the data encoded on a METAR might look like VRB004KT (variable direction blowing at four knots). If the wind speed is greater than six knots and the wind direction varies, the data encoded on a METAR might look like "32014KT 290V350". Translation: the wind direction was 320 degrees and the wind speed was 14 knots, but the direction varied from 290 to 350 degrees. Such a varying wind direction might occur in the immediate wake of a cold front. Variable wind directions are always encoded in the clockwise direction (just for the record).
Okay, back to decoding the Concord METAR. 1 3/4SM translates to a horizontal visibility of one and three-fourths statute miles (opens in a new window). Visibilities below one fourth of a mile appear as M1/4SM in METARS from automated stations.
+RA BR is the present weather in this case. "+RA" represents heavy rain, while "BR" is the METAR code for mist. You should become familiar with the other codes for precipitation and restrictions to visibility.
| QUALIFIER INTENSITY OR PROXIMITY 1 | QUALIFIER DESCRIPTOR 2 | WEATHER PHENOMENA PRECIPITATION 3 | WEATHER PHENOMENA OBSCURATION 4 | WEATHER PHENOMENA OTHER 5 |
|---|---|---|---|---|
| - Light Moderate2 + Heavy VC In the Vicinity3 | MI Shallow PR Partial BC Patches DR Low Drifting BL Blowing SH Shower(s) TS Thunderstorm FZ Freezing | DZ Drizzle RA Rain SN Snow SG Snow Grains IC Ice Crystals PE Ice Pellets GR Hail GS Small Hail and/or Snow Pellets UP Unknown Precipitation | BR Mist FG Fog FU Smoke VA Volcanic Ash DU Widespread Dust SA Sand HZ Haze PY Spray | PO Well- Developed Dust/Sand Whirls SQ Squalls FC Funnel Cloud Tornado Waterspout4 SS Sandstorm SS Duststorm |
- The weather groups shall be constructed by considering columns 1 to 5 in the table above in sequence, i.e. intensity, followed by description, followed by weather phenomena, e.g. heavy rain shower(s) is coded as +SHRA
- To denote moderate intensity no entry or symbol is used.
- See paragraph 8.4.1.a.(2), 8.5, and 8.5.1 for vicinity definitions.
- Tornados and waterspouts shall be coded as +FC.
OVC010 represents the current sky condition, which, at this time, was overcast at 1000 feet (the three-digit code corresponds to the ceiling (or cloud base) in hundreds of feet). In general, please note that METARS can list data about more than one layer of clouds. Moreover, when the sky is obscured, METARS should include the vertical visibility in hundreds of feet. For example, VV004 corresponds to an obscured sky with a vertical visibility of 400 feet.
A3005 is the altimeter (opens in a new window) setting - in this case, 30.05 inches of mercury.
09/07 represent the temperature and the dew point reported to the nearest degree Celsius (more precise data sometimes appear near the end of METARS - I will showcase the "T group" in just a moment or two). In this observation, the temperature was 9 degrees Celsius and the dew point was 7 degrees Celsius.
RMK stands for "Remarks." There are a multitude of remarks (see heading 12.7.1 of the Federal Handbook (opens in a new window)). In this case, A02 indicates that the automated station has a precipitation sensor (A01 means that the automated station does not have a precipitation sensor).
CIG 007V013. When the ceiling (as measured by a ceilometer (opens in a new window)) is less than 3000 feet and variable, this group typically appears in METARS. In this case, the ceiling was variable between 700 and 1300 feet.
SLP177 indicates the sea-level pressure in millibars using the same convention as on a standard station model (1017.7 mb, in this case).
P0015 is the hourly liquid precipitation (in hundredths of an inch). In this case, 0.15 inches of rain fell in the hour ending at 12Z.
60056 represents the three- or six-hour liquid precipitation (in hundredths of an inch). In this case, 0.56 inches of rain fell in the six-hour period ending at 12Z. for the record, six-hour totals appear at 00Z, 06z, 12Z and 18Z. Three-hour totals appear at 03Z, 09Z, 15Z and 21Z. 60000 translates to a trace of liquid precipitation during the three- or six-hour period.
70066 indicates the total 24-hour liquid precipitation ending at 12Z (in hundredths of an inch). In this case, 0.66 inches fell at Concord from 12Z on May 12 to 12Z on May 13.
T00890072 indicates the hourly temperature and dew point to the nearest tenth of a degree Celsius. You will likely want to follow this group as you monitor your forecasts (note the differences between these actual 12Z observations and the 09/07 temperature / dew-point group). The "0" after the "T" indicates that the temperature and dew point are higher than 0 degrees Celsius (a "1" will follow the "T" when the dew point temperature and /or the temperature is / are less than 0 degrees Celsius). In this case, the 12Z temperature at Concord was 8.9 degrees Celsius and the dew point was 7.2 degrees Celsius.
10094 represents the highest temperature, in tenths of a degree Celsius, during the six-hour period ending at 12Z (in this case). If the digit following the "1" is a "0," then the temperature is higher than 0 degrees Celsius (a "1" following the "1" indicates that the temperature is less than 0 degrees Celsius). So the highest temperature at Concord between 06Z and 12Z on May 13, 2006, was 9.4 degrees Celsius. For the record, the "1" group is reported at 00Z, 06Z, 12Z and 18Z.
20089 indicates the lowest temperature during the six-hour period ending at 12Z (in this case). If the digit following the "2" is a "0," then the temperature is higher than 0 degrees Celsius (a "1" following the "2" indicates that the temperature is less than 0 degrees Celsius). So the lowest temperature at Concord between 06Z and 12Z on May 13, 2006, was 8.9 degrees Celsius. Like the "1" group, the "2" group is reported at 00Z, 06Z, 12Z and 18Z.
53018 indicates the pressure tendency (the "5 group"). The digit following the "5," which can vary from 0 to 8, describes the behavior of the pressure over the past three hours (for guidance, consult the table below). The last three digits represent the amount of pressure change in tenths of a millibar. Thus, the pressure at Concord increased 1.8 mb in the three-hour period ending at 12Z on May 13, 2006.
I realize that translating one METAR hardly qualifies as an entire lesson, but at least you now know the general guidelines and where to find information in case you run across a METAR that gives you pause. I encourage you to expand your aptitude for decoding METARS. They hold a lot of information! A good place to view raw METARs and their decoded counterpart is the surface section of the Real-Time Weather Data page at NCAR (opens in a new window). Notice by entering the 4-letter ICAO identifier for any station you can get a series of raw or translated METARS, which can be a great way to practice your skills!