Bri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4 Posted (9 years 9 months 3 weeks 5 days 23 hours ago) and read 4710 times:
I did a search for this topic, but the relevant postings did not specify ATIS, ASOS/AWOS, METAR, etc. Based on my particular experience related below, I'd like to ask this question anyway.
Sample ATIS recording: "Denver International Airport Information India, 1753 Zulu. Visibility 10. Temperature 10. Dewpoint -4. Altimeter 3018. Light rain, mist. Ceiling 7000 broken...."
Does the "seven thousand" in the ATIS broadcast refer to altitude AGL or MSL? I used to think it was MSL, but DEN has a field elevation of 5431, and I could swear I once heard something like "ceiling three thousand broken." This doesn't make sense because the cloud ceiling can't be below the field elevation. I only heard it once though, on a particularly bad weather day. Can someone please clarify this for me?
Bri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 3, posted (9 years 9 months 3 weeks 5 days 21 hours ago) and read 4602 times:
Thanks for the responses. I guess in a lot of places, there's little difference between AGL and MSL with respect to cloud levels. How are these measured, anyway? Is it a precise WX radar measurement, pireps, or a combination?
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I don't know if that particular sensor is used for the ASOS/AWOS installation though...
If it comes from an ASOS and you have the AUTO annotation in the METAR then it's entirely off the ASOS sensor, there is no human intervention, and no PIREPs are used.
So sometimes you can have a cloud sit on top of the airport right over the sensor, and it's reporting a 1000ft ceiling and there are no clouds anywhere else in sight for 10 miles around the airport, but the ASOS will report that cloud at 1000ft. Or the other way around, clouds all around the airport, but the hole over the ASOS sensor will have the ASOS report CLEAR BELOW 12000.
[Edited 2005-02-05 00:23:49]
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