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12/31-1/1 Northern/Central Plains Cyclone


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Might as well start a thread since this will likely be some of the more interesting weather across the plains in quite a while. Guidance has been strongly suggestive of a strong Pacific wave amplifying across the CONUS as it interacts with the PV across Canada. Much of the amplification of this wave will actually be due to the intensity of the ejecting IPV anomaly as the phase interaction with the PV doesn't seem to occur until after this system has progressed well into the Lakes/OV. Given the latest guidance, the big news with this storm will be winds across portions of the plains as well as a localized winter advisory type event across MN. What makes the winter aspect interesting is the wind potential combined with the snow across parts of MN.

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Alright time to get this thread going again. High wind warnnings have been riased for much of the high plains. There is going to be a major frontal surge as well as the cold front ejects into the central high plains. We are looking at some extensive pressure rises on the order of 6-12 hpa. It is a classic high/low pattern across the Great Basin/Plains, respectively, but this time, there will be an intense tropopause undulation forcing a much more signfiicant than average mass response in the low/mid levels, i.e., quite a but of subsidence behind the front. Going to be a fun bora wind event.

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The RGEM is definitely one of the more aggressive models as it digs the ejecint PV a little farther S then goes negative as it ejects northward. Not completely out of the question...the ejecting PV is impressive to say the leas...although it seems a bit wet even if it were to verify synoptically.

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If you want to get an idea of how challenging this forecast is...note the 500 hpa spread in the SREF only 24 hrs in. About 3/4ths of the members show tropofolding...while a few are weaker and suggest much less PV advection. Either way will be windy...but the ejecting of the trop undulation is key in how intense the frontal surge is...and how the cyclone develops across the plains. And the top undulation itself is definitely a meso-alpha feature, but it has wide ranging overall synoptic effects.

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It has to be inferred here based on trop maps and the corresponding 50-0 maps on the deterministic guidance, but even here it can be relatively inferred using 500 vorticity alone and the strongest gradient. Look where there is. ARW2/3 are great examples. But the 500 vorticity gradient and vorticity advection (all inferred I should add) can be correlated to where the tropopause undulation is aloft since you normally don't see that type of vorticity gradient.

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URGENT - WEATHER MESSAGE...CORRECTED

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

253 PM CST FRI DEC 30 2011

...STRONG WINDS DEVELOPING NEW YEARS EVE...

.A DEEP AREA OF LOW PRESSURE AND A STRONG COLD FRONT WILL SWEEP

EAST ACROSS MINNESOTA SATURDAY...TO THE LAKE SUPERIOR REGION BY

EARLY SUNDAY MORNING. STRONG NORTHWEST WINDS OF 30 TO 35 MPH WITH

GUSTS AROUND 55 MPH WILL BE POSSIBLE OVER WEST CENTRAL AND

SOUTHWEST MINNESOTA DEVELOPING AFTER 3 PM SATURDAY. THIS WILL

SPREAD EAST OVER CENTRAL AND SOUTHERN MINNESOTA INTO WEST CENTRAL

WISCONSIN THROUGH SATURDAY EVENING AS THE WEATHER SYSTEM MOVES

EAST. THE STRONG WINDS WILL CONTINUE THROUGH THE DAY ON SUNDAY AS

WELL. A WIND ADVISORY IS IN EFFECT FROM THE AREA SOUTH OF A LINE

FROM NEAR LITTLE FALLS...THE TWIN CITIES AND DURAND....FROM 3 PM

SATURDAY UNTIL 6 PM SUNDAY. WINDS WILL ONLY VERY SLOWLY DIMINISH

DURING THE NIGHT SUNDAY AND INTO MONDAY.

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The RGEM is definitely one of the more aggressive models as it digs the ejecint PV a little farther S then goes negative as it ejects northward. Not completely out of the question...the ejecting PV is impressive to say the leas...although it seems a bit wet even if it were to verify synoptically.

0z Nam trying to follow the 18z rgem idea?

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All the guidance coming in west and stronger now. 0Z GFS looking much more similar to the RGEM now too. Classic example of what an upper air sample can do when dealing with deep tropopause undulations. This is going to be a fun event tomorrow.

Do the winds look strong at the time of precip or do they come in after? Could be travel trouble later tomorrow.

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Nice stripe of snow painted across the area by the 12z NAM. Slightly heavier than the previous two runs, with 0.35" now at MSP.

Looks like it really starts getting crazy around here after 6z when all the crazies will be on the road!

This one will be a fun one to watch!

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PUEBLO CO
821 AM MST SAT DEC 31 2011
..TIME...   ...EVENT...	  ...CITY LOCATION...	 ...LAT.LON...
..DATE...   ....MAG....	  ..COUNTY LOCATION..ST.. ...SOURCE....
	    ..REMARKS..
0743 AM	 NON-TSTM WND GST 1 E MONARCH PASS	    38.50N 106.31W
12/31/2011  M95.00 MPH	   CHAFFEE		    CO   AWOS
	    SUSTAINED WIND 84 MPH WITH GUSTS TO 95 MPH. CDOT AWOS.

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17Z SmartCast Update: Looking at areas around the Brainerd, MN with highest snow accumulations through 04Z, with around 1.6" possible, with the heaviest accumulation rates of .6" from 22 to 00Z. Snow looks to begin across the Minneapolis around 03Z time with potential of 3-4" of snow, coupled with strong west-northwest winds up to 35 mph. Also Nebraska areas of Helig Field, Alliance, Sidney with some light snow accumulations of around an 1", but strong winds will be the main focus with wind gust over 60mph possible through 22Z. Full data update http://smartwxmodel.net

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