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Rockies/Plains Winter Storm Dec 2-4


Srain

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Guidance is suggesting some impressive totals for the Rockies into the Plains. With a 1-2 punch of upper air disturbances ejecting out of AZ, it is becoming likely we will have our first fairly widespread Winter Storm event of the season.

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By the way, for those wondering....the 12z NAM gives MSP around 1.04" liquid. It also has a bit of a p-type issue with the first batch of precipitation. Surface temps warm up quite a bit, deep enough surface warm layer for the NAM to depict rain as the p-type for a period Saturday AM. So it would be a SNOW-RAIN-SNOW transition.

Again, given the performance of the NAM around here lately, this is all taken with a grain of salt right now.

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As much as the snow lover in me wants to believe the 12z NAM....the NAM in general, in my opinion, has been JUNK around here all fall...(not that the GFS has been any better)

*patiently waiting for the Euro*

I share your opinion about the Nam...just nice to see some qpf plotted over the area for once on a model. lol Last 3 months total precip here has been 1.06.

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This should make for an interesting late week into early next week...

EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

142 PM EST WED NOV 30 2011

VALID 12Z SAT DEC 03 2011 - 12Z WED DEC 07 2011

A STRONG POSITIVE MID-LEVEL HEIGHT ANOMALY ACROSS THE NORTHEASTERN

PACIFIC WILL WORK IN CONJUNCTION WITH A WEAKER NEGATIVE MID-LEVEL

HEIGHT ANOMALY ACROSS HUDSON BAY TO HELP MAINTAIN A

POSITIVELY-TILTED LONGWAVE WAVE TROUGH EXTENDING FROM HUDSON BAY

TOWARD THE FOUR CORNERS REGION THROUGH NEXT TUE 06 DEC. EARLY

PRELIM PRESSURES/FRONTS WERE CONSTRUCTED USING A BLEND OF THE 00Z

WED ECMWF/12Z TUE ECMWF/12Z ECMWF ENSEMBLE MEAN GUIDANCE FOR THIS

CYCLE.

UPDATED MORNING PRELIMS UTILIZE 00Z ECMWF/00Z ECMWF ENS MEANS AND

00Z UKMET DAYS 3-5 AND ECMWF/ECMWF ENS MEANS DAYS 6 AND 7

TUES/WED.

12Z GFS REMAINS CONSISTENT WITH ITS 00Z RUN WHILE 12Z CMC REMAINS

MORE SIMILAR TO THE ECMWF OF LEAVING SIGNIFICANT ENERGY BEHIND AS

A CLOSED LOW IN THE SOUTHWEST BY DAYS 4-5 AND TAKES MORE NRN

STREAM ENERGY EASTWARD. THE 12Z UKMET HOWEVER HAS SWITCHED TOWARDS

THE GFS/CMC SOLUTION FROM ITS PRIOR TREND CLOSER TO THE 00Z ECMWF.

12Z ECMWF HAS ALSO SWITCHED TOWARDS THE GFS SOLUTION THIS RUN.

THIS WAS THE ORIGINAL ECMWF SOLUTION SEVERAL DAYS AGO WITH THE

EARLIER GFS RUNS LOOKING LIKE YESTERDAYS AND THE OVERNIGHT 00Z

ECMWF. THIS DOES NOT INSPIRE CONFIDENCE. HPC PROGS WILL REMAIN

UNCHANGED FOR NOW BUT WITH LOWER CONFIDENCE THAN PRIOR ISSUANCE

WITH OR WHEN ANY SUCCEEDING RUNS CONVERGE ON A BETTER AGREED UPON

SOLUTION THEN HPC GUIDANCE WILL CHANGE.

WESTERN US TO CENTRAL-SOUTHERN PLAINS...

DOWNSTREAM OF THE CLOSED MID-UPPER PACIFIC ANTICYCLONE...A REGION

OF ABOVE NORMAL TEMPERATURES SHOULD PERSIST ACROSS THE PACIFIC

NORTHWEST. FURTHER SOUTH...THE MODELS SHOW THE DEVELOPMENT OF A

CLOSED MID-UPPER LEVEL CYCLONE OVER THE SOUTHWEST US WITH THE

POSSIBILITY OF THE EJECTION OF ONE 500 MB WAVE FROM THE LOW ON SAT

INTO THE CENTRAL PLAINS AND BEYOND. THIS WOULD LEAD TO AN AREA OF

PRECIP CROSSING THE CO/NM ROCKIES AND THEN THE CENTRAL-SOUTHERN

PLAINS AND MID-UPPER MS VALLEY.

WHILE THE LEAD WAVE EJECTS...ANOTHER WAVE DEVELOPING ON THE BACK

SIDE OF THE TROUGH IS SHOWN IN THE 12Z TUE-00Z WED

ECMWF...SUPPORTED BY THE UKMET/CANADIAN GLOBAL. THIS LEADS TO

ANOTHER CLOSED 500 MB LOW ON SUN IN THE SOUTHWEST. AT 12Z SUN THE

GFS/GEFS MEAN STARTS TO ALLOW THE LOW TO MOVE EAST...WHILE THE

ECMWF/ECMWF ENSEMBLE MEAN MOVE IT MORE SLOWLY. GIVEN THE HIGHER

HEIGHTS BUILDING TO THE NORTH OF THE CLOSED LOW AND IN AN ALMOST

REX BLOCK CONFIGURATION...PREFER THE SLOWER MOVING CLUSTER OF

SOLUTIONS. THE 00Z ECMWF/CANADIAN GLOBAL SHOW THIS CLOSED LOW

FINALLY MOVING EAST TUE NIGHT 06 DEC INTO WED 07 DEC.

NORTHERN PLAINS/UPPER MS VALLEY/GREAT LAKES/NORTHEAST...

THE MODELS ARE IN BETTER THAN AVERAGE AGREEMENT IN SHOWING THE

NEXT DEEP LAYER TROUGH MOVING ACROSS THE NORTHERN PLAINS AND UPPER

MS VALLEY ON SAT 03 DEC AND SUN 04 DEC...WITH DIFFERENCES

REGARDING SHORTWAVE ENERGY WHICH MAY PROPAGATE THROUGH THE MEAN

TROUGH. THE 12Z TUE ECMWF/18Z GFS SHOW POTENTIAL FOR A WAVE TO

CLOSE OFF TO A CLOSED LOW BY 12Z TUE AS THE WAVE PROGRESSES ACROSS

THE LAKES AND HEADS TOWARDS NY/NEW ENGLAND..THEN OFF THE COAST WED

07 DEC. THE 00Z ECMWF SHOWS THE AMPLIFICATION OF ONE OF THE

EMBEDDED 500 MB SHORTWAVES INTO A CLOSED LOW FURTHER SOUTH IN

OH/PA TO THE MID ATLANTIC COAST. THIS WAS ALSO PRESENTED 3 RUNS

AGO IN THE ECMWF. FOR NOW...BLEND OF OPERATIONAL 0Z ECMWF AND ITS

ENS MEAN USED TO HANDLE THE DIFFERENCES.

ON DAY 7...THE HIGH HEIGHTS OVER ALASKA AND THE NORTHEAST PACIFIC

LEADS TO AMPLIFICATION OF A CENTRAL CANADA TROUGH. AS THIS

OCCURS...A STRONG COLD FRONT IS FORECAST TO MOVE SOUTH ACROSS THE

NORTHERN PLAINS AND POSSIBLY THE UPPER MS VALLEY. TIMING AND

PHASING DIFFERENCES WITHIN THE CANADIAN 500 MB TROUGH LEAD TO

TIMING DIFFERENCES OF THE COLD FRONT ARRIVAL AND PROGRESSION.

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This is a tough forecast, but if I were a betting man, I would take middle of the road for now. I hate saying that, but the GFS lately has been way too weak with the +AO, so from a standpoint of the northern stream, that would favor something along the lines of an ECMWF solution. However, these low level fronts have a tendency to leak southward faster than progged, so something along a 12Z GFS/EC compromise seems the best at this juncture. post-999-0-96415300-1322688805.png

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As much as the snow lover in me wants to believe the 12z NAM....the NAM in general, in my opinion, has been JUNK around here all fall...(not that the GFS has been any better)

*patiently waiting for the Euro*

Totally agree. The NAM has been total garbage. I have been very disappointed with it. It is weird because it was superior to he old NAM when it was running in parallel mode, but since being unveiled in September it has been junk. It has struggled especially with this system with all sorts of crazy solutions that simply don't make much sense.

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I am beginning to lose confidence in the ECMWF solution...which is farthest N. Besides the fact this system is a product of two cold frontal surges which tend to leak a bit farther S than progged, the guidance has been very slowly trending towards a strongly amplified E Pac ridge with a farther W cutoff low across the 4 corners. All in all, this results in a slower ejection of the wave and more time for the northern stream/arctic front to surge south. Fits the seasonal trend of deep troughs to tend more towards a positive tilt configuration...resulting in weaker cyclogenesis and more frontal wave setups. This system looks no different. Unfortunately the 0Z GFS possibly leaning towards the 12Z CMC would be a realistic scenario.

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I am beginning to lose confidence in the ECMWF solution...which is farthest N. Besides the fact this system is a product of two cold frontal surges which tend to leak a bit farther S than progged, the guidance has been very slowly trending towards a strongly amplified E Pac ridge with a farther W cutoff low across the 4 corners. All in all, this results in a slower ejection of the wave and more time for the northern stream/arctic front to surge south. Fits the seasonal trend of deep troughs to tend more towards a positive tilt configuration...resulting in weaker cyclogenesis and more frontal wave setups. This system looks no different. Unfortunately the 0Z GFS possibly leaning towards the 12Z CMC would be a realistic scenario.

Now the 0z CMC dumps 0.41 qpf for LBF where the 0z GFS gives you nothing. :lol:

post-252-0-19000000-1322717672.gif

post-252-0-62079000-1322717683.gif

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man, i wish there were people posting obs for the snow developing along the front range of the Rockies...hmmm, I guess there would have to posters from that area on this board...i'd love to see pics and hear what people have to say about the current conditions...

24.8 degrees

4" of fluffy snow. (or maybe a bit more)

It stopped snowing.

The pics wouldn't look as the pics I took of snowstorms on Oct. 26 or Nov. 2.

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man, i wish there were people posting obs for the snow developing along the front range of the Rockies...hmmm, I guess there would have to posters from that area on this board...i'd love to see pics and hear what people have to say about the current conditions...

6-7" on elevated surfaces in Highlands Ranch, but winds have been gusty at times so huge variations point to point

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What does the Euro show for Rochester?

RST

SAT 12Z 03-DEC   0.9	-1.1	1021  	92  	97	0.06 	560 	543	
SAT 18Z 03-DEC   1.3	-1.9	1021  	99  	99	0.09 	559 	543	
SUN 00Z 04-DEC   0.5	-1.8	1017  	99  	99	0.26 	555 	541	
SUN 06Z 04-DEC   0.0	-3.4	1013  	98  	98	0.34 	548 	537	
SUN 12Z 04-DEC  -1.7	-5.9	1013  	93  	98	0.05 	542 	531	
SUN 18Z 04-DEC  -2.4	-7.9	1020  	81  	65	0.01 	542 	527	


Euro 0.81
Ukie 0.80

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