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Christmas Storm II


Cold Rain

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Just caught up reading the overnight posts. This is getting so exciting! I love how most of the models are agreeing with each other and with so much consistency. It's just hard to think there is a way we don't get some snow here on Christmas day. That would be amazing!

And props to Matthew East for putting it in the local forecast already. I think the ones for the Triangle are just saying rain right now.

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Why does HPC just talk about the east coast ? I guess places like Atlanta, Birmingham, Nashville won't be effected ?

They do say things in there about the SOUTHEAST coast, and phasing over the Tennessee Valley. Very nice writeup, and it's clear they are all in with the Euro.

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

902 AM EST TUE DEC 21 2010

VALID 12Z SAT DEC 25 2010 - 12Z TUE DEC 28 2010

...CONTINUED WET ACROSS THE PACIFIC NORTHWEST...

...BELOW NORMAL TEMPS FROM THE PLAINS EASTWARD...

...POTENTIAL EAST COAST WINTER STORM SAT-MON...

THE NORTH ATLANTIC OSCILLATION INDEX REMAINS NEGATIVE THIS MORNING

WITH A LARGE POSITIVE MID-LEVEL HEIGHT ANOMALY EXTENDING FROM

GREENLAND WESTWARD TOWARD HUDSON BAY WHICH IS BLOCKING THE

UPSTREAM FLOW...MUCH OF WHICH IS EXPECTED TO ORIGINATE FROM AN

INTENSE POLAR JET STREAM TRAVERSING THE BASE OF A QUASI-STATIONARY

UPPER CYCLONE OVER THE GULF OF ALASKA THROUGH THE MEDIUM RANGE

PERIOD.

MODEL AGREEMENT WITH THE LARGER-SCALE ASPECTS IS QUITE GOOD TO

BEGIN THE PERIOD. HOWEVER...THIS IS NOT THE CASE OVER THE CENTRAL

CONUS WHERE THE FLOW BEGINS TO SPLIT...WITH THE 00-06Z GFS/00Z

CANADIAN FASTER AND MORE AGGRESSIVE THAN THE 00Z ECMWF/UKMET IN

ALLOWING THE FLOW TO PHASE OVER THE MISSISSIPPI/TENNESSEE VALLEYS

BY DAYS 4/5. SEVERAL ASPECTS...INCLUDING RECENT SATELLITE TRENDS

OVER THE EASTERN PACIFIC SHOWING AN INTENSE POLAR JET TRAVERSING

THE WESTERN PERIPHERY OF AN ACCOMPANYING UPPER TROUGH...HIGHER

SPATIAL RESOLUTION OF THE ECMWF...AND MORE SOPHISTICATED

INITIALIZATION OF THE ECMWF...FAVOR AN ECMWF-LIKE SOLUTION VERSUS

THE 00-06Z GFS...IN ALL AREAS. HOWEVER...GIVEN THAT EVEN THE ECMWF

CAN NOT ACCOUNT FOR UNCERTAINTY IN INITIAL CONDITIONS...FEEL IT IS

MOST PRUDENT TO ADD INCREASING WEIGHT FROM ITS OWN ENSEMBLE MEAN

THROUGH THE ENTIRE PERIOD. THUS...THE UPDATED PRESSURES/FRONTS

WILL BEGIN WITH A 90/10 ECMWF/ECMWF ENSEMBLE MEAN BLEND

RESPECTIVELY DAY 3...WHILE GRADUALLY TRANSITIONING TOWARD A 40/60

ECMWF/ECMWF ENSEMBLE MEAN BLEND RESPECTIVELY BY DAY 7.

REGARDING SIGNIFICANT IMPACTS...THE PACIFIC NORTHWEST EXTENDING

PERHAPS AS FAR SOUTH AS THE SIERRAS WILL REMAIN UNDER THE

INFLUENCE OF AN UNUSUALLY STRONG POLAR JET STREAM EMBEDDED WITH

PERIODS OF HEAVY PRECIPITATION. DAYS 4/5 AND DAYS 6/7 QPF ACROSS

THE WEST ARE EXPECTED TO RANGE BETWEEN 2 AND 5 INCHES POSSIBLY

HIGHER...WITH THE LAST 2 RUNS OF THE ECMWF AND ITS MOST RECENT

ENSEMBLE MEAN USED AS A 1ST GUESS. MEANWHILE...THE EVOLVING TROUGH

OVER THE GREAT LAKES/OHIO VALLEY EARLY IN THE PERIOD FAVOR BELOW

NORMAL TEMPERATURES FOR ALL AREAS FROM THE PLAINS EASTWARD...WITH

SUBFREEZING TEMPERATURES POSSIBLY RETURNING THE ENTIRE GULF COAST

REGION AND MUCH OF FLORIDA BY DAYS 6/7. FINALLY...AN ECMWF-LIKE

SOLUTION FAVORS A WINTER STORM BEGINNING TO DEVELOP NEAR THE

SOUTHEAST COAST BY DAY 4 BEFORE ACCELERATING UP THE EAST COAST

DAYS 5/6. IT IS STILL TOO EARLY TO BE DEFINITIVE WITH THE PRECISE

DETAILS INCLUDING TRACK OF THIS SYSTEM AS MODEL SPREAD CONSIDERING

THE SPLIT-FLOW UPSTREAM BECOMES QUITE LARGE. WHILE THE 00Z ECMWF

IS MOST PREFERRED...MANY OF ITS OWN ENSEMBLE MEMBERS ARE BOTH

FASTER AND SLOWER WITH THE TRACK OF THE LOW WHICH HAS HUGE

IMPLICATIONS FOR THE ENTIRE EAST COAST. THUS...GIVEN THE

UNCERTAINTIES AND SPREAD...THE UPDATED TRACK ALONG THE EAST COAST

WAS MORE HEAVILY WEIGHTED TOWARD ITS OWN ENSEMBLE MEAN ESPECIALLY

LATE IN THE PERIOD.

JAMES

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CLOSED OFF AT 78! Awating the precip to explode over the SE. (and an SLP sig for that matter!)

3l7VW.gif

Yeah this run definately looks good and better than the 06z run. The shortwave/closed low is a good 300 to 400 miles southwest of the 06z run and doesn't phase as early. Looks like a winner.

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This is a huge change from 6z. Matches very closely to the Euro... EE Rule in effect!

Looks to be in lock step with the 0z EC with the ULL placement in TX, which is very impressive considering we are talking about the NAM at 84hrs. It does have a piece of energy in IL, while the 0z has it in IA, with the main phasing parcel coming down through ND. No big deal on that at this range, what is going on in TX is the main thing to take away from this run, and that looks great!

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