Decoding METARS

[wxwatcher]

Here's a little quiz for you on MERTAR codes. It's to see how perceptive you are when you read a weather observation.
What are the differences suggested by the following METARS:

KABC METAR 121450Z AUTO 27010KT CLR 19/15 A3004 RMK A02

KDEF METAR 121450Z 27010KT CLR 19/15 A3004 RMK A02

KGHI METAR 121450Z 27010KT SKC 19/15 A3004

Note: I did a post a response to a question about this subject a few months back in a different forum. I thought it would be of interest to some of you here. I'll check back in a couple of days and see if anyone has the right answer..

Good Luck.. :-)


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Comments and opinions are my own and do not reflect those of my employer.

[1739T]

Appearently no body is going to bite on this one.

What are the differences?

[SeaAir]

Well, since no one else has posted a reply, I'll take a stab at it...

First the stuff that is common to all three reports. They are all for the 12th of the month at 1450Z, wind is from 270 at 10 kts, temperature is 19 C, dewpoint is 15 C, and the altimeter setting is 30.04 inches of Hg.

Now at KABC, this is a fully automated site (ASOS/AWOS) which does not have any human intervention (AUTO), there are no clouds at or below 12,000 feet (CLR), and the automated site has a precipitation discriminator (A02)(it can tell the difference between rain and snow).

At KDEF, this is the same as KABC except that a human has logged on and may have input some information manually. This is not a fully automated report. (I presume however that they did not enter the CLR otherwise it would have been SKC or something else.)

Finally, at KGHI, this is a manned site which has clear skies with 0/8 coverage (SKC).

How did I do wxwatcher?

[This message has been edited by SeaAir (edited 11-07-2000).]

[wxwatcher]

SEAAIRE WINS THE PRIZE!! (Now, if I can only remember where they stashed it.) ;-)

Absolutely correct. The difference I was looking for was the fully automated vs "augmented" automated vs manual (human) observations.

The first was a fully automated observation as indicated by the term AUTO in the body of the observation.

The second was the "augmented" observation where a human monitors the system and can make changes before the observation is sent out. BTW.. If the sky condition is really clear, most augmented stations will not change the coding which actually means "Clear below 12,000" which is the maximum certified cloud hight the system can detect. Now, it there was a higher scattered layer, you may see something like SCT200 as a sky condition.

(A word of caution here.. I have noticed a couple of times where the METAR showed one condition and a SPECI three to four minutes later, usually with a time between H+56 and H+02, showed something drasticly different. On a few of those I checked, I found that the human observer had augmented the observation to show the actual current conditions in the METAR. He/she then turned around to get some cofee or answer a phone or whatever, but missed the automated system doing the SPECI, EVEN THOUGH THE CONDITIONS HAD NOT CHANGED!! Now I routinely check with the location if i can when I see something like that.)

The last was an example of a straight manual or human observation. The observer actually goes outside and looks at the current weather conditions as well as the older equipment used for winds, temps, dew point and altimeter settings. (There are fewer and fewer of these every month.)

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Comments and opinions are my own and do not reflect those of my employer.

[This message has been edited by wxwatcher (edited 11-08-2000).]

[This message has been edited by wxwatcher (edited 11-08-2000).]