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Thursday 11 December 2008

From the Sublime to the ridiculous? A weather phenomena!

Greetings dear readers.

I was idly reading the Buffalo office of the National Weather Service text bulletin on today's forecast and quote part of it below...

LOOKING AT A CROSS SECTION FROM NEAR GRAND RAPIDS MICHIGAN TO NEAR
ALBANY...PLACING THE LINE THROUGH MUCH OF OUR FORECAST AREA...I
NOTICED A NOTICEABLE WESTWARD EXTENSION OF MID LEVEL FRONTOGENESIS
DURING THIS 00Z-12Z PERIOD WHICH MAY ALSO EXTEND THE WESTERN EDGE OF
LIGHT SNOW AS FAR WEST AS LAKE ERIE. OF COURSE...THE GFS IS MORE
ROBUST IN SHOWING THIS UPWARD SLOPING FRONTAL BOUNDARY THAN THE
NAM...BUT BOTH MODELS DO SHOW SUFFICIENT FRONTOGENESIS AND MOISTURE
FROM 700MB TO 500MB FOR SNOW TO FORM ALOFT. THE BIG QUESTION IS IF
THE SNOW WILL REACH THE GROUND AS THERE IS A VERY DRY UNDERLYING
LAYER THROUGH WHICH ANY SNOW MUST FALL...MAYBE ALL WILL SUBLIMATE
BEFORE REACHING THE GROUND AND WE`LL JUST HAVE SOME REALLY NICE
VIRGA. IN EITHER CASE...WILL EXTEND CHANCE POPS TO COVER THE REST OF
THE FORECAST AREA FROM THE FINGER LAKES TO THE WESTERN EDGE...40
POPS FOR NOW.

See their web page HERE

Well, there's a couple of words there which I find interesting. You don't often see sublimation mentioned. That is not ridiculous, it's where a solid changes to a gas without going through the liquid state. More often in meteorological discussions it is mentioned in the context of snow lying on the ground disappearing although the temperature is below freezing.

Secondly, there's the mention of virga. That is nothing to do with a little blue pill, it's precipitation that does not reach the ground.

I have to say I've met one of the forecasters from Buffalo NWS office, David Sage. He gave a truly fabulous lecture on thunderstorms at an FAA sponsored "Wings" event some years ago. I was impressed by his passion for the subject, his ability to pass on vital information to the pilot community, and above all his wonderful use of English. Look for his name on the text page linked above! Send him an email.....

Cheers.

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