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Storm Threat Dec 26-28 Period


Ralph Wiggum

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Here is the latest 6-10 day forecast for the cpc...the 1st analog that particular date has nothing, but 6 days later was the christmas day storm that brough a foot plus in the pocs and 4-12 for the nw burbs and rdg to abe but the 2nd one dropped 13 inches of snow on philly...3rd analog dropped 5 inches on phl..

610analog.off.gif

One of the analogs is December 20, 2009 which was the day after the huge MA Miller A that year.
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Here is the latest 6-10 day forecast for the cpc...the 1st analog that particular date has nothing, but 6 days later was the christmas day storm that brough a foot plus in the pocs and 4-12 for the nw burbs and rdg to abe but the 2nd one dropped 13 inches of snow on philly...3rd analog dropped 5 inches on phl..

Wow. 12/24/1966! A favorite from my youth. Very heavy snow on the evening of the 24'th in Delco

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HPC discussion. Like the GEFS over Euro

MODEL CHOICE...

THE 00Z GFS LOOKS ENTIRELY PLAUSIBLE AND FITS WELL WITH BOTH THE

00Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN. THE LOW TRACK THE GFS

DEPICTED FROM THE SOUTHERN PLAINS TO OHIO VALLEY ON DAYS 5-7

MATCHES CONTINUITY FROM THE OVERNIGHT PACKAGE AND IS IN THE MIDDLE

OF THE BEST CLUSTERING OF ENSEMBLE LOW TRACKS. THIS GAVE US

MODERATE TO STRONG CONFIDENCE IN USING THE 00Z GFS AS THE PRIMARY

BASIS FOR OUR FRONTS/PRESSURES...WITH RELATIVELY LOWER WEIGHTING

ON THE ENSEMBLE MEANS EVEN THROUGH DAY 7. WE ALSO GAVE SOME WEIGHT

TO THE 00Z CANADIAN WHICH OFFERS A SIMILAR PROGRESSION. THE 00Z

ECMWF WAS LARGELY DISCOUNTED AS BEING TOO AMPLIFIED AND SLOW WITH

THE PLAINS/MIDWEST CYCLONE AND ALSO WITH A TROUGH APPROACHING THE

WEST COAST LATE IN THE PERIOD. THE ECMWF WAS A CLEAR

OUTLIER...ESPECIALLY WITH RESPECT TO DEPTH...COMPARED TO EVEN ITS

OWN ENSEMBLE MEMBERS. ONE KEY POINT AT DAY 7...IS THAT OUR MODELS

OF CHOICE...GFS/GEFS MEAN/CANADIAN...ALL POINT TOWARD A HAND-OFF

FROM THE CYCLONE OVER THE OHIO VALLEY TO A DEVELOPING LOW ALONG

THE MID ATLANTIC COAST. THIS IS NOW REFLECTED IN OUR FORECAST.

...IMPACTS...

THE STORM SYSTEM OF INTEREST THIS PERIOD WILL ENTER THE WEST COAST

ON DAY 3 AND DIG INTO THE SOUTHWEST ON DAY 4...BRINGING

RAIN/SNOW/POTENTIAL WINTER STORM CONDITIONS TO THE MOUNTAINS. AT

THE SAME TIME...BLOCKED FLOW AT HIGHER LATITUDES WILL ALLOW A

STACKED CYCLONE OVER EASTERN CANADA TO FORCE MORE ARCTIC AND

MODIFIED ARCTIC AIR DOWN INTO THE CENTRAL U.S...SETTING THE STAGE

FOR ANOTHER SNOW EVENT WHEN THE STORM EJECTS FROM THE SOUTHWEST

STATES. EXPECT THIS TIME THAT THE PERSISTENT BLOCK OVER EASTERN

CANADA WILL SUPPRESS THE TRACK OF THE SURFACE LOW INTO THE OHIO

VALLEY RATHER THAN THE GREAT LAKES. AT PRESENT TIME...THE MOST

LIKELY SNOW SWATH APPEARS TO BE ACROSS NORTHWEST OK INTO KS/MO

CHRISTMAS DAY AND NIGHT...CONTINUING TOWARD NORTHERN IL/IN.

RAIN/THUNDER WILL OCCUR FARTHER SOUTH TO THE GULF COAST...SWEEPING

EASTWARD. MODELS INDICATE COLD AIR DAMMED INTO THE MID ATLANTIC

REGION IN ADVANCE OF THE SYSTEM...WHICH MAY RESULT IN A MIXTURE OF

PRECIPITATION TYPES TOWARD DAYS 6/7. IF THE COASTAL LOW/NOR'EASTER

WERE TO FORM AS FORECAST...IT APPEARS PER THE 00Z GFS/GEFS

INFORMATION THAT THE SNOW LINE WOULD INDEED REACH THE COAST AND

THE MAJOR CITIES IN NEW ENGLAND. THIS IS AT DAY 7...HOWEVER...AND

THEREFORE IS LESS CERTAIN. THE ECMWF ENSEMBLE IS A BIT SLOWER AND

FARTHER WEST...SUGGESTING MORE WARM ADVECTION WHICH WOULD PUSH THE

RAIN/SNOW LINE

INLAND.

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I might be wrong but I think we want the Christmas wave to overperform, flatten heights, and strengthen/become a 50/50 low.

From what I've been reading elsewhere I think you're right....somehow we need the X-mas wave stronger and further south....probably a pipe-dream but miracles do happen.

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