Changing Weather

by Glen Moyer


As a graduate of Carrol Teitsworthís Liberty Balloon School it was one of my proudest moments; that moment when I could unhesitatingly raise my hand and volunteer to decipher aloud a Flight Service terminal forecast. Yes sir! Balloonist Extraordinaire, that was me.
Then a few years later DUATs came along and spoiled all the fun with their "Plain Language" translations. Oh, sure, they still printed the weather in those nonsensical strips of jargon, then they wrote it all out for us so we pilots didnít have to strain our brains.
Well, hold everything, the FAA is about to put the fun back into reading weather forecasts! Beginning June 1st, the method of reporting terminal forecasts and surface observations will be changed to bring the United States more in line with our international neighbors. To wit, our weather reporting will be revised so as to more fully comply with the International Civil Aviation Formats. Heck, they wonít even have the same names. Terminal Forecasts will now be called TAFs (Aerodrome Forecasts) but Surface Observations will henceforth be known as METARs (Aviation Routine Weather Report). Even winds aloft (Fds), area forecasts (Fas) and pilot reports (Pireps) will begin to incorporate the new weather coding and station identifiers. So - get out those Big Chief tablets and a sharp number 2 pencil and letís go back to school...

METAR
A METAR (or SPECI if issued as a SPECIal Report) will look similar to the old surface observations, but there are some key changes, mostly in where important information is found in the string of numbers and letters. To help remember the sequence, think of the 3Ws at the beginning - Where, When and Wind. This works for the new TAF as well!
Letís decode the following METAR:
KDFW201955Z 22015G25KT 1/2SM R28R/2600FT TSRA OVC10CB
18/16 A2992 RMK

Where? KDFW is the ICAO station identifier. DFW is the familiar 3 letter identifier. These will now be preceded by a "K" for the contiguous United States.
When? 201955Z is the 20th day of the month. 1955Z is the time, 1955 Zulu or UMT.
Wind? 22015G25KT is reported as the 3-digit (not the old 2) direction to the nearest 10 degrees. 15 is the 2 or 3 digit speed. G means "gusting" 25KT is the 2 or 3 digit maximum speed and the unit of measurement (KT-knots).
A few additonal notes. 000000KT is now calm winds. If the wind is greater than 6 knots and expected to vary by more than 60 degrees it would be reported as 180V260 (180 degrees varying to 260 degrees). VRB is the new term for variable winds at less than 6 knots replacing the old LV or light and variable. RMK is for "remarks" at the end of the report where peak winds will be reported if speeds are in excess of 25 knots.
Visibility? 1/2SM means one/half statute mile visibility. Miles and fractions are also reported, i.e. 2 3/4 for two and three/quarter miles.
R28R/2600FT is runway language that as balloonists we can generally ignore. But donít make the mistake of stopping here on the report. (For those interested R means runway, 28R is the runway designator (R-right, L-left, C-center). 2600FT is visibility in feet.
Significant Present Weather? This is why I said donít stop decoding yet. TSRA, Thunderstorm with moderate rain. The format is a two character descriptor followed by a two character weather phenomenon. (TS- thunderstorm, RA-moderate rain.) How do you know if the rain is light, heavy or moderate? If light the RA is preceded by a minus sign (-), heavy is indicated by a plus sign (+) and no sign means moderate.
Clouds? OVC101CB specifies cloud amount, height and type. OVC-overcast clouds are present at 010-one thousand feet, consisting of CB-cumulonimbus clouds. Cloud height is reported in hundreds of feet. When clouds are composed of towering cumulus or cumulonimbus TCU or CB will follow cloud height.
Additionally, clouds will now be categorized based on the 8 octas of the sky:
SKC - Sky clear, FEW - 1 to 2 octas, SCT - 3 or 4 octas, BKN - 5 to 7 octas, and OVC or 8 octas. VV/// means indefinite ceiling, height not available.
Temperature/Dew Point? 18/16 is now reported in degrees Celcius. (See the conversion chart on page ?? , copy it and put it in your wallet!) In this case, the temperature is 64 F with a dewpoint of 61 F.
A2992 is the altimeter setting at the familiar 29.92 inches of mercury. The "A" means inches of mercury for the U.S. So far we are being spared millibars or hectopascals.
As noted earlier, RMK is for remarks.

There, now wasnít that fun! The same process works for the new terminal forecasts, or TAFs. Of course both Contel and GTE, the providers of DUATs service say they will adopt the new format but will continue with their plain language translations. To really understand the new system, pick up a copy of the FAAís latest publication New Aviation Weather Reports: METAR/TAF to which this reporter (and this article) are deeply indebted. A call to my area FSDO produced a half dozen copies by return mail so that I could share them with other area pilots. After reading the booklet, youíll find the rear cover is a handy decoder card (and you didnít even have to send in a boxtop!) which you might want to stash in your logbook pouch for later reference.
So get those booklets and start studying. These changes are to take effect June 1st. Otherwise you may find yourself totally OVC.


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