122

In the aviation world, they don't use AM/PM times. Instead, all times are assumed to be AM unless they're labeled NOTAM.

https://explainxkcd.com/3024/

top 9 comments
sorted by: hot top controversial new old

The comic before this had to do with miles per hour versus knots, so I think Randall Monroe is in flight school.

[-] HK65@sopuli.xyz 52 points 1 week ago

So I actually went and tried to decode this because I was horrified that I didn't understand half of this. Turns out I don't usually see freedom units or volcanic ash tornadoes.

  • METAR - That's just specifying this is a meteorlogical report as opposed to something else like a TAF or a NOTAM
  • KNYC - This should be the airport the report is given for, KNYC doesn't exist, but if it did, it would be somewhere in the US since it starts with a K
  • 251600Z - means the report is dated for the 25th, 16:00 UTC
  • 18035G45KTS - this is the wind, coming from 180 degrees, 35 knots gusting 45, so a lot of wind
  • 6SM - so this was weird, but it's just US weirdness, visibility 6 statute miles, so equivalent to the 9999 message everywhere else
  • VCFCFZVA - in the vicinity funnel cloud, freezing, volcanic ash (freezing volcanic tornadoes, yay!)
  • +BLUP - heavy blowing unknown precipitation, so a lot of something coming your way
  • NOSIG - no significant change expected, this is your life now
  • LTG OHD - surprisingly accurate, lightning overhead
  • A3808 - again, weird US shenanigans, altimeter setting 38.08 inches of mercury, which is not really consistent with that major storm but I digress
  • RMK - remarks, this is how meteorogists say "oh, by the way"
  • A02 - I'm an automated weather station who also can differentiate precipitation (pretty high strung for someone who just announced +BLUP)
  • SLP130 - sea level pressure is 1013 hPa, which means that this airport is at around 2100 m above sea level

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.

[-] HK65@sopuli.xyz 2 points 4 days ago

Thanks for that info, in fact I'm just preparing for my PPL over on this side of the ocean.

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.

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.

You'll hear AWOS systems say "Visibility. More than. One. Zero."

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.

[-] mkwt@lemmy.world 7 points 1 week ago

The altimeter setting should be referenced to sea level as well. Which means it doesn't agree with the SLP.

[-] HK65@sopuli.xyz 2 points 1 week ago

I was giving a benefit of doubt and assuming it must be a QFE setting or IDK.

38.08 is veery high for a QNH anyways

[-] neidu3@sh.itjust.works 21 points 1 week ago

As someone who can actually read METAR, my frontal lobe is currently in agony.

Yeah you can't help but try and it goes right off the rails at the precip report.

this post was submitted on 13 Dec 2024
122 points (99.2% liked)

xkcd

8968 readers
169 users here now

A community for a webcomic of romance, sarcasm, math, and language.

founded 2 years ago
MODERATORS