Ok, before I got sidetracked by some exciting weather in the past few days, I mentioned how we code weather observations and send them off to the National Weather Service. Now that we went back to having somewhat normal weather that gives me a chance to elaborate on how to decode METAR. Here is the example I gave in my previous entry:

KMWN 160159Z 28052KT 50SM FEW010 FEW030 FEW100 SCT130 OVC180 M06/M08 RMK ACSL E ACSL OH

Now I am going to break this down piece by piece.

KMWN: this is our 4 letter station identifier. Just like KPIT is Pittsburghs station identifier.

160159Z: the first two digits, 16 indicate the day of the month. The next 4 digits followed by the letter Z indicate the time of the observation in Zulu time. Zulu time is also known as UTC (Universal Time Coordinated), and Greenwich Mean Time. Basically it is a universal time meaning that when it is 12Z at Mount Washington it is also 12Z in Tokyo. To get the equivalent Eastern Standard Time, simply subtract 5 hours from the Zulu time. So this observation was taken at 8:59 p.m. EST or 0159Z.

28052KT: the first three digits, 280 are the wind direction in degrees. Zero degrees is North, 90 degrees is east, 180 degrees is south, and 270 degrees is west. So at 280 degrees, this is considered a west wind. The next two digits followed by the letters KT are the sustained wind speed in knots (nautical miles per hour). In this case, the wind was at 52 knots. One knot is equivalent to 1.15 miles per hour. Also, if the wind had been gusting 10 or more knots beyond the sustained wind, a gust would have been coded in this format: 28052G63KT.

50SM: this is the visibility in statute miles, in this case 50. A statute mile is the mile that you are used to seeing on road signs and such. The only reason it is specified is to differentiate between nautical miles.

FEW010 FEW030 FEW100 SCT130 OVC180: these are the cloud layers at the time of observation, in this case there were 5. The first 3 letters describe the type of cloud cover (the choices are FEW, SCT or scattered, BKN or broken, and OVC or overcast) while the last 3 digits give the height of the cloud base in hundreds of feet above the station level. So we had a layer of few clouds at 1000 feet, a layer of few at 3000 feet, etc.

M06/M08: this gives the air temperature and dewpoint in degrees Celsius. The first letter and following 2 digits are the air temperature. The second group is the dewpoint. The letter M is telling us that the measurement is below zero. So in this case the air temperature was 6 degrees below zero Celsius and the dewpoint was 8 degrees below zero Celsius.

RMK ACSL E ACSL OH: this is the remarks section, indicated by the RMK at the begninning. This can sometimes be the most difficult section because there is a wide variety of data that can be coded here. It would take me way to long to go over all the possibilities. In this case ACSL E stands for altocumulus standing lenticular to the east, and ASCL OH stands for altocumulus standing lenticular overhead.

Ok, so now you are a pro at decoding METAR, right? Well at least now if you had to decode some METAR to save your life you could do it. :-)

Until next time...

Brian

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