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Author Topic: Aviation weather from the AWOS  (Read 6716 times)

Offline Jonathan_tcu

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Aviation weather from the AWOS
« on: August 10, 2005, 10:16:24 PM »
I don't expect many replies on this, but I've been hearing ATC comments and seeing for myself at NavCanada's weather info, and noticing these AWOS's like those at Toronto Island, Muskoka, Moosonee, Eartlon, etc... always report 2 + layers of an overcast ceiling, or rain (-RA) under CLR skies, etc.  Does anyone have information on these robotic equipment pieces out there around the world? lol.



Offline davolijj

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AWOS
« Reply #1 on: August 12, 2005, 08:53:07 AM »
I'm not sure what the Meteorological Service of Canada guidelines are there, but the US National Weather Service uses a practice called summation layer amount which precludes more than one OVC layer from being reported.  The priciples of this practice are that once the celestial dome has been populated with 8/8 of sky cover, OVC will the the final layer in the absence of an indefinite ceiling.

I can buy -RA with CLR however because the contraction CLR is only reported at automated stations and indicates "clear below 10,000."  I've often seen precipitation or Virga falling from layers higher than that on warm days, usually from stratiform clouds.  -RA with SKC I would have a hard time believing.

Offline Jonathan_tcu

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Aviation weather from the AWOS
« Reply #2 on: August 14, 2005, 08:20:56 AM »
The AWOS is weird.  I hear controllers from Toronto who laugh at the way the ceilings are displayed in the metars, like 4 + layers of a broken ceiling (sounds like a broken record)  and another controller who makes me laugh from the East Radar sector at Toronto who says " overcast one-thousand feet and overcast at three thousand feet...ha...I don't know how they do that!" lol

Offline Lexxx

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Aviation weather from the AWOS
« Reply #3 on: August 16, 2005, 05:32:45 PM »
Quote from: Jonathan_tcu
The AWOS is weird.  I hear controllers from Toronto who laugh at the way the ceilings are displayed in the metars, like 4 + layers of a broken ceiling (sounds like a broken record)  and another controller who makes me laugh from the East Radar sector at Toronto who says " overcast one-thousand feet and overcast at three thousand feet...ha...I don't know how they do that!" lol


They can do that because (in Canada anyway) Enironment Canada classifies an overcast layer when 90% to 100% of the sky is covered as determined by a laser ceilometer.  If the laser determines 90% of the sky is obscured, any additional layers detected as the laser continues up are also recorded.

The same basically applies to a broken sky condition. 50% to 89% of the sky covered.

I know it seems odd to have several overcast layers, and to VFR pilots it doesn't matter too much, but it can be "good information" for an IFR aircraft to know about as many layers as possible as he continues up.

A laser can determine layers of cloud that a human observer cannot, and so the concept of what should constitute an overcast layer has changed.

Here's a link to more info if you're interested.

http://www.msc-smc.ec.gc.ca/msb/manuals/awos/chap1_e.html#126_e

Cheers

Offline Jonathan_tcu

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Aviation weather from the AWOS
« Reply #4 on: August 16, 2005, 05:37:10 PM »
OK.  That makes perfect sense.  I get more answers from you guys than from any other source.  I think it is obvious that there CAN be one layer or two, or three of an overcast ceiling.