ATIS/AWOS/ASOS


#1

How accurate are ATIS/AWOS/ASOS thermometers? A few days ago it was 31 C at my house. The PAE, BFI, and SEA METARs were saying it was around 20 C. I put my thermometer in the sun and left it for an hour. Are some ATIS/AWOS in the shade?


#2

Of course they are! They’re also protected from wind and precipitation. They’re measuring air temperature, not “exposed to sunlight” temperature.

To answer your other question, they’re very accurate.


#3

Here is a quick blurb from the National Weather Service for their Co-op observers.

This is basically how a temperature sensor is “sited”

Temperature sensor siting: The sensor should be mounted 5 feet +/- 1 foot above the ground. The ground over which the shelter [radiation] is located should be typical of the surrounding area. A level, open clearing is desirable so the thermometers are freely ventilated by air flow. Do not install the sensor on a steep slope or in a sheltered hollow unless it is typical of the area or unless data from that type of site are desired. When possible, the shelter should be no closer than four times the height of any obstruction (tree, fence, building, etc.). The sensor should be at least 100 feet from any paved or concrete surface.

Usually, the NWS uses shelters for temp gauges to keep them out of the sun, like this one:

crh.noaa.gov/mkx/coop/coop-equip.php

An ASOS array does it a bit differently than you might think

Temperature and dew point

Automated airport weather stations use a temperature/dew point sensor (hygrothermometer) designed for continuous operation which normally remains on at all times, except during maintenance.

The measurement of temperature is simple compared to the dew point. Operating under the principle that electrical resistance varies with temperature, a Platinum wire resistive temperature device measures the ambient air temperature.
See this link from wikipedia

en.wikipedia.org/wiki/Automated_ … er_station

So, if you are hanging your thermometer out in the direct sun, you’re doing wrong!!!


#4

I would like to dedicate my seven hundred and eighty seventh post to the Boeing 787 which I hope with come out soon so I can see it!

Thanks, I was really confused about all this.

BTW: I did a run and the effect on my body was more like 31 degrees than 20. :laughing:


#5

that just means your internal body thermometer is getting old. :unamused:


#6

ATIS is only updated by the hour. I have found AWOS to be very reliable.


#7

Just to clarify . . .

ASOS and AWOS are automated weather observing systems. ATIS is the recording done at an airport with a weather observation, notams, active runways, etc . . . ATIS wx information is taken from the ASOS or AWOS at the airport (literally read from a computer screen).

I’ve worked at 2 towers with ASOS and 1 with AWOS. Both are very accurate with wind speed, temperature/dew pt, and altimeter, but ASOS is a lot better at cloud height and cover. ASOS observations can be modified by certified wx observers; to my knowledge, AWOS can’t, but I can’t prove it.

ASOS has a feature where the controlling agency can select if they want the same hourly observation to go out for the entire hour, of if they want the most up-to-the-minute observation to go out (call the ASOS at your local airport when the tower is open, the time will always end with 53 or a time close to that, and the observation will be the same the whole hour after that. Call in the middle of the night when the tower is closed, and it will give the current time and the actual observation at that moment).