Block setting back up west of Greenland - Looks like LI may be in the crosshairs.
Posted by
JAC on 1/1/2011, 3:05 pm
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
216 PM EST SAT JAN 01 2011
VALID 12Z TUE JAN 04 2011 - 12Z SAT JAN 08 2011
...FINAL MEDIUM RANGE DISCUSSION...
FINAL PROGS MADE NO CHANGES EXCEPT TO SHOW LOWER PRES OVER THE MID
ATLANTIC STATES FRI-SAT VICINITY OF THE LARGE 500MB HEIGHT FALLS.
THE GEFS MEAN HAD EXCELLENT CONTINUITY WITH MOST MAJOR FEATURES ON
THE MAP.
THE MOST NOTABLE FEATURE AFFECTING NORTH AMERICA THIS FIRST WEEK
OF 2011 WILL BE ANOTHER STRONG HIGH LATITUDE BLOCKING EPISODE AS A
HUGE POSITIVE HEIGHT ANOMALY WORKS ITS WAY WSW FROM SRN GREENLAND
TO N CENTRAL CANADA...WITH ONLY GRADUAL WEAKENING DURING THE
PERIOD. SW OF THE BLOCK...LOW HEIGHTS AND COLD AIR WILL BE WILL BE
DOMINANT ACROSS MUCH OF S CENTRAL AND FAR SERN CANADA INTO THE
NERN QUADRANT OF THE LOWER 48. THE LOCATION OF THE COLD AIR IS A
GOOD FIT TO TELECONNECTIONS ON THE STRONG POSITIVE ANOMALY WORKING
WSW FROM SRN GREENLAND. SIMILAR TO MUCH OF DECEMBER...THE REGION E
OF THE ROCKY MTNS WILL BE BACK TO BELOW NORMAL TEMPS. THE 00Z/01
AND 12Z/01 GEFS MEANS WERE A BIT COLDER THAN THE 00Z DETERMINISTIC
ECMWF THIS PERIOD FOR MUCH OF THE CENTRAL AND ERN CONUS. THOUGH
SOMEWHAT UNCHARACTERISTIC...THIS SEEMS REASONABLE GIVEN THE
MAGNITUDE OF THE BLOCKING MOVING ACROSS FAR NERN AND NRN CANADA.
NEW ENSEMBLE SPAGHETTI PLOTS SHOW THE SOLUTION FROM OFF THE CA
COAST ACROSS THE SWRN STATES REMAINING HIGHLY UNCERTAIN DAYS
3-5/TUE-THU. THERE IS STILL QUITE A BIT OF SPREAD IN SOLUTIONS IN
THE NEW 12Z/01 DETERMINISTIC MODELS WITH THIS FEATURE. ONE CLUSTER
HAS AN UPPER LOW DRIFTING SLOWLY EWD ALONG 30N TOWARDS 120W BY
THU/FRI DAYS 5-6.
OUR FINAL PROGS HAVE MADE CORRECTIONS TO THE 500MB PATTERN ALONG
THE W COAST THAT HAVE SHIFTED AWAY FROM THE EARLY BLEND OF 80%
GEFS ENSEMBLE MEAN TO BEING 40% EACH OF THE ECENS MEAN AND GEFS
MEAN BY DAYS 5-7. FINAL 500MB PROGS HAVE BEEN FURTHER ADJUSTED
TOWARDS THE NEW 12Z/01 ECMWF. RECEIPT OF LATEST ENSEMBLE SPAGHETTI
PLOTS HIGHLIGHTED A POTENTIAL PROBLEM SHOWING UP OVER THE NE
PACIFIC AND WRN NOAM DAYS 5-7. THE 00Z/01 ECMWF WAS DEVELOPING A
NEW TROF NEAR 130W THU-SAT W OF THE VANCOUVER/BRITISH COLUMBIA
AREA. WE SUSPECTED THAT THE 00Z ECMWF MIGHT BE CORRECT IN LOWERING
HEIGHTS DAYS 5-7 IN A BROAD AREA OFF THE W COAST OF NOAM...BUT WE
WERE NOT SURE ABOUT HOW RAPIDLY THE FALLS WOULD ERODE THE RIDGE
ALREADY IN PLACE OVER SWRN CANADA AND THE PACIFIC NW. THE NEW 12Z
ECMWF IS IN FACT MUCH SLOWER TO BRING HEIGHT FALLS INTO THE
PACIFIC NW DAYS 6 AND 7....AND WE FAVOR ITS LATEST TREND.
12Z DETERMINISTIC MODELS: THERE IS GENERAL AGREEMENT ON THE LARGE
SCALE PICTURE: A FAST MOVING SHORTWAVE OF MODERATE AMPLITUDE
RACING ACROSS THE NE QUADRANT OF THE NATION TUE...A VORTEX
PLUNGING SE FROM WRN HUDSON BAY TUE ACROSS THE UPPER MIDWEST TO
THE NRN MIDDLE ATLANTIC REGION BY FRI; A LEFTOVER UPPER LOW
MEANDERING SOMEWHERE TO THE W OF SRN CA; AND A SLOWLY PROGRESSIVE
RIDGE MOVING INTO WRN CANADA THU DAY 5 THAT EVENTUALLY GETS
FLATTENED BY HEIGHT FALLS TO THE W THEREAFTER. AS USUAL...THE
DEVIL IS IN THE SMALLER SCALE DETAILS. THIS IS PARTICULARLY TRUE
CONCERNING POSSIBLE EXPLOSIVE CYCLOGENESIS FRI DAY 6 VICINITY OF
LONG ISLAND IN RESPONSE TO LARGE 500MB HEIGHT FALLS MOVING INTO
THE MID ATLANTIC STATES AT THAT TIME. SPREAD OF UPPER LOW
SOLUTIONS FOR FRI RANGE FROM NY STATE IN THE 12Z/01 GEFS ENSEMBLE
MEAN/12Z ECMWF TO WV/KY IN THE NEW CANADIAN. SRN NEW ENG HAS THE
HIGHEST THREAT FOR ANOTHER REALLY BIG SNOW FROM THIS SYS. WHATEVER
THIS DEVELOPING STORM DOES...WE ARE HIGHLY CONFIDENT OF ANOTHER
EPISODE OF STRONG GUSTY WINDS AND BITTER WIND CHILLS IN ITS WAKE
THE END OF NEXT WEEK. THE NEW 12Z ECMWF WAS ON THE N SIDE OF THE
GUIDANCE BY DAY 6 HAVING ITS UPPER LOW OVER NY STATE.
FLOOD
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