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METARs and TAFs have been around since before the high-speed internet made data transmission instantaneous (and they are based on Surface Aviation Observation (SAO) and Terminal Forecasts (TF) for current weather conditions before June 1, 1996) so they use a somewhat cryptic method for encoding weather data. However, once you learn how to decode them they aren’t many surprises. Occasionally you see something different and I’ve collected some of them in this post.

For help in decoding, I use the ASOS Guide for Pilots. Even though you can get the decoded information on-line, it’s still a good idea to learn the abbreviations because sometimes the information isn’t translated. Also, XM weather is displayed on the Garmin GPS Map in coded form, so knowing the codes makes it easier to see what’s ahead.

KSBP 091256Z COR 26003KT 4SM BR OVC007 08/07 A2994 RMK AO2 CIG 005V009 SLP138 T00830072 TSNO $

This is the first time I saw the COR notation. COR indicates a correction to a previously disseminated report.. In the remarks that the ceiling (CIG) is 500′ with a vertical visibility of 900′ (005V009). Note the $ at the end of the METAR. The symbol $ will appear if the ASOS detects that a preventative maintenance check is needed.

TAF KNFG 0415/0515 VRB05KT 9999 SCT200 QNH3008INS
TAF AMD KVBG 041738Z 0417/0521 15015KT 9000 -RA SCT010 BKN013 OVC020 620908 QNH3004INS

These are TAFs for Camp Pendleton and Vandenberg AFB. Military airfields are the only places I’ve seen QNH forecast. We don’t normally refer to the altimeter setting as QNH—we generally just refer to it as the altimeter setting. It is the atmospheric pressure measured at mean sea level. If reported in inches—as above—it is the setting on your pressure altimeter that yields field elevation.

The first two digits of 9999 are the visibility in meters. The notation 9999 means greater than 6 miles. In the Vandenberg AFB example visibility is 9000 meters or about 6 miles.

KLAX 271453Z 00000KT 1/4SM R25R/3500VP6000FT FG VV001 17/16 A2996 RMK AO2 SLP142 T01670161 51014

If you fly out of smaller airports, you probably don’t see runway visual range data. R25R/3500VP6000FT is decoded as: R—RVR, 25R—for runway 25 right, 3500V—3500 varying to, P6000—greater than 6000, FT—measured in FT (RVR can also be reported in statute miles).

KMNN 080015Z AUTO 02018KT 8SM UP OVC013 M04/M07 A2993 RMK AO2 P0000

This is an automated report and the sensor detects precipitation but doesn’t know what kind, hence UP—Unknown Precipitation. Since the temperature is minus 4 °C it could be snow or freezing rain.

KSBP 250356Z AUTO 32006KT 8SM FU CLR 12/09 A2995 RMK AO2 SLP142 T01220094 TSNO

The code FU was fairly common this summer when much of California was on fire. It is derived from the French word for smoke—fumar.

FM0000 36027G47KT 2SM RA BR OVC008
FM2200 01030G48KT 1SM +RA BR OVC008

Nothing hard to decode about this TAF for Providence, RI. There is a storm on the way with winds from 360 at 27 kts gusting to 47 kts. The winds shifts slightly and the rain gets worse later in the day.

This entry was posted on Saturday, September 27th, 2008 at 8:56 am and is filed under Weather. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.