The Skinny on the Forecast

Monday, 24 June 2013 | Weather

We’ve been in a very wet pattern the past few days, with some areas west of Madison receiving 5″-7″ of rainfall between the 21st and 23rd of June. People are especially interested in precipitation forecasts for the next couple days, which is why I couldn’t help excerpting this bit of text from the morning forecast discussion out of the Milwaukee/Sullivan National Weather Service office for Monday, June 24th. It illustrates the sausage-making process that happens behind the scenes when you read the rather un-descriptive public forecasts that are issued by the NWS.

“…PERSISTENT 850-700 MB WARM ADVECTION WITHIN BROAD 850 MB LOW LEVEL JET AND MOIST AIRMASS SHOULD YIELD SCATTERED TO NUMEROUS THUNDERSTORMS TODAY AND TONIGHT.

TIMING AND LOCATION DIFFICULT AS USUAL WITH CONVECTION AND ASSOCIATED MESOSCALE OUTFLOW BOUNDARIES BUT PRECIPITABLE WATER VALUES WILL BE IN 130-160% OF NORMAL RANGE SO POTENTIAL FOR HEAVY RAIN TO CONTINUE. FRANKLY YOU COULD EXTEND THE FLASH FLOOD WATCH UNTIL WEDNESDAY MORNING BUT AFTER DISCUSSING THE MATTER WITH SURROUNDING WFOS SEEMS THAT WE SHOULD FOCUS ON THE NEXT 12-24 HOURS. AFTER MUCH DELIBERATION DECIDED TO MATCH UP WITH ARX AND EXTEND THE WATCH UNTIL 10 AM ON TUESDAY.

THESE SITUATIONS ARE ALWAYS DIFFICULT BECAUSE TRYING TO FORECAST QPF FOR THE WHOLE AREA WITHOUT KNOWING WHICH COUPLE OF COUNTIES WILL GET HIT WITH 3-5 INCHES OF RAIN OR MORE IS ALMOST IMPOSSIBLE. SO WE BROAD BRUSH 0.50 TO 1.00″ QPF KNOWING THAT SOME AREAS WILL GET VERY LITTLE RAIN AND OTHERS MUCH MORE.”

As you can tell, the forecasters are between a rock and a hard place in terms of what they can present to the public in a few words, so learning to read and understand the forecast discussions is extremely useful to those who have regular interests outdoors. If you need some of the technical terms translated, they are hyperlinked in the forecast discussion original.

This link to the NWS LaCrosse (“ARX”) site shows observed precipitation through June 23rd.

 

rm

Weather
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Rob McClure
Rob McClure is the Weather Emperor, and rains his forecast into your ears during Global Revolutions and In Our Backyard.

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