Wednesday, February 21, 2007

How to read a METAR

I know, there's no reason for anyone but pilots to know how to read this. But the observant among you may have noticed a little widget on the right-hand side: weather.

It provides weather information for the closest airports I could find for me and the four regulars. You'll notice that each site is listed with a four-letter code; these airport codes are essentially the same as the FAA codes, with one distinction: These are the international codes, so the letter "K" is put in front to indicate we're in the U.S.

This widget provides a cool little glance at the weather - provided you know how to read it. So that's what I'll try to explain here.

First, the codes: KDCA is Ronald Reagan Washington National Airport (me); KBDL is Bradley International in Connecticut (Matt); KGBM is Binghamton Municipal (P.J. - sorry, it's the closest I could find); KCVG is Cincinnati-Northern Kentucky International (Mandy; at least I think that's still close to her); KSUN is Friedman Memorial in Sun Valley, Idaho (my kick-ass brother-in-law).

To the left of each code is a little colored button; it reads either "VFR" or "IFR". VFR stands for Visual Flight Rules; it basically means clear weather. "IFR" is Instrument Flight Rules, meaning that the weather is less than ideal for visual flight.

Now, onto the more complex stuff.

The first set of numbers always ends with a "Z". This simply tells you the date and time; the first two numbers are the day number, the last four are the 24-hour time of the observation. The Z tells us that time is Zulu time, or GMT (five hours ahead of us on the east coast).

Auto, if it's there, tells us it's an automated observation.

The next set: wind direction and speed. The first three numbers are the direction the wind is coming from; remember, 090 will be out of the east, 180 out of the south, 270 out of the west and 360 from due north. The last two numbers tell of the wind speed in knots, hence the "KT". If you see a "G" in the middle, that indicates maximum gusts; if there's a "V", the direction or speed is variable.

Next is visibility in statue miles. After that is the most critical part of the METAR: precipitation and sky condition, if any. There are any number of combinations of symbols - and they're deciphered here - but suffice it to say if there's a "-" in front of the term, it's light; no descriptor, it's moderate; a "+" means it's heavy. So "+SN BL" means it's probably a good idea to leave the Cessna in the hangar today (heavy blowing snow).

Following the precip remarks, you'll see cloud levels. The link above gives a good, detailed explanation of what it means, but basically it's broken down into few clouds (FEW), scattered (SCT), broken (BRK), overcast (OVC) and CB (cumulonimbus cloud, i.e. a thunderstorm).

Next are two numbers that are separated by a slash. This is the temperature and dewpoint in Celsuis; an "M" in front of either number means minus. Last is the current barometer, which starts off with the letter "A". That's because a plane's altitude indicator is called an altimeter; pilots dial in this number to help the plane guage how far above sea level they are.

RMK means the end of the primary METAR. The stuff that follows really is of no concern to us, but the FSStation link again provides good info on this.

At any rate, I hope you guys like the widget. I'm going to try to surf around to try to find some more cool stuff to add on here. Let me know if you like it.

-- BARON VON COUNTERCULTURE'S GROOVY PURPLE DIRIGIBLE: I kept forgetting to post this, but this may be my new favorite music video of all-time. It's Gnarls Barkley's "Smiley Faces," a brilliant concept executed perfectly. And it helps that this song is outstanding, a lot better than "Crazy," IMO.


ME said...

Can you decipher those weather codes without referring to the guides? Yikes.

BTW, thanks for turning me on to that song.

Brian said...

You do it a few times, you get used to it. A quickie guide: First thing is time/date of observation. Second is wind - look for the KT (knots), which indicates a speed. What other speed would a weather observation contain?

SM is visibility - think statue miles. The next set (or sets) are sky condition until the set with a slash, which is temp/dewpoint.

That help?