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xkcd #3024: METAR
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this post was submitted on 13 Dec 2024
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American flight instructor here, yeah we use statute miles for visibility, nautical miles for distance and knots for speed, feet in altitude, celsius for temperature and dewpoint and inches of mercury for barometric pressure.
METARs will report up to 10 statute miles visibility. You'll hear AWOS systems say "Visibility. More than. One. Zero." in their sound board kind of way. 6SM is on the chart and surprisingly clear for a freezing torcano.
Missing from this METAR are cloud coverage and heights. Should be something like BKN005 OVC008 for the weather it's reporting, that would be broken clouds at 500 feet AGL and overcast at 800 feet AGL. I figure if we've got volcnadoes going.
Also missing is the temperature and dewpoint report, which both read in degrees celsius as two digits each with a slash in between. So there should be a section that looks like "...+BLUP NOSIG BKN005 OVC008 18/17 A3808..." I figure to have broken clouds at 500 feet the dewpoint has to be one degree below the ambient temperature.
I've never seen an altimeter setting that high, a "standard day" is 29.92 in. Hg. What the hell would have pushed 7.1 inches of mercury up the barometer? The tsunami that accompanied the erupting volcano washing ashore and inundating the AWOS machine?
A02 or A01 is, as far as I know, appended to every METAR that is generated by an ASOS or AWOS machine. That mark will be missing if it was generated by a human, say at a larger airport that has an ATIS system.
"NOSIG" should be in the Remarks section AFAIK, and I've never seen an automated system generate forecast information like that.
Thanks for that info, in fact I'm just preparing for my PPL over on this side of the ocean.
I fly from a bigger airport with its own CTR and ATIS, but the METAR is automated, except it just says AUTO, no A01/02. Wonder if that's also an EASA/FAA difference.
We are pampered then, we get a fluid pleasant female voice announcing "visibility one-zero kilometres or more" on the automated ATIS reports. I'm not sure that AWOS and ASOS exist here though, but we have CTRs and ATIS systems almost touching each other in these parts everywhere anyway.
US flight instructor since 2010. Haven't flown in a little while though.
AWOS and ASOS systems (ASOS being slightly more fasisticated) are the automated systems you'll find at smaller uncontrolled airports; they transmit an automated voice reading the weather on a VHF COM frequency and often link back to the National Weather Service (or however the byzantine soon to be gone series of government agencies that could plausibly be in charge would deal with it) to generate METARs you'll get from the usual scumbags, and when you see a weather map on the news with the temperatures scattered around, they're almost all from airport systems, it's where almost all of the government thermometers are.
A lot of them are decades old and use the sound board method of making a machine talk. Short little clips of a guy saying a word or two played in sequence. I actually prefer them to a lot of the actual voice synths they had in use. For some dumb reason most of them are male voices and fairly deep so they're down in the noise floor, higher pitched/women's voices carry on radios better.
ATIS systems will either still be a loop of an actual person's voice recording, or I started to hear some that had a Stephen Hawking style voice synth that weren't easy to read back.