Incredible. Block back in place
Posted by JAC on 12/27/2009, 9:35 am
Add the pressure gradient from the 1040mb High south of Hudson Bay --> Huge Winds!



PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
859 AM EST SUN DEC 27 2009

VALID 12Z THU DEC 31 2009 - 12Z SUN JAN 03 2010

TELECONNECTIONS WITH A NEGATIVE ANOMALY...THE POLAR VORTEX...OVER
THE WESTERN CANADIAN ARCHIPELAGO FAVOR TROUGHING ACROSS EASTERN
CANADA AND THE NORTHEAST AS WELL AS A SOUTHERN STREAM TO THE
WESTERLIES NEAR THE US/MEXICAN BORDER. THE MODELS GENERALLY FAVOR
THESE IDEAS.

PERHAPS EQUALLY IMPORTANT TO THE OVERALL PATTERN IS THE
REDEVELOPMENT OF VERY STRONG BLOCKING OVER SRN GREENLAND BY THU
THAT DRIFTS SLOWLY WWD INTO THE SRN DAVIS STRAIT NEXT WEEKEND.
THIS STRONG HIGH LATITUDE BLOCK FAVORS SUPPRESSED WESTERLIES
ACROSS THE LOWER 48 STATES WELL EWD INTO THE ATLANTIC. THESE
SUPPRESSED WESTERLIES..JOINING FORCES WITH THE SRN STREAM NEAR THE
US/MEXICAN BORDER AND THE MODERATE EL NINO...FAVOR AN ACTIVE STORM
TRACK ACROSS THE GULF OF MEXICO TOWARDS THE S ATLANTIC COAST.    

IN THE EASTERN HALF OF THE COUNTRY...THE ECMWF CONTINUES TO WAVER
A BIT CONCERNING THE TIMING OF THE FRONTAL WAVE/COASTAL LOW
EXPECTED TO MOVE FROM THE GULF OF MEXICO UP THE SOUTHEAST COAST TO
NEAR THE 40N/70W BENCHMARK...WITH ITS MOST RECENT RUN ON THE FAST
SIDE OF ITS PAST 36 HOURS OF RUNS THOUGH SIMILAR TO THE TIMING
SEEN ON ITS RUNS FROM 2-3 DAYS AGO.  

ALTHOUGH THE 12Z MULTI-MODEL ENSEMBLE LOW MEMBERS WERE TIGHTENING
UP THEIR DISTRIBUTION SOMEWHAT /SLIGHTLY OUTPACING THE OPERATIONAL
00Z ECMWF EARLY ON/...THERE CONTINUES TO BE TIMING ISSUES WITH THE
GEFS MEMBERS GENERALLY SHOWING QUICKER SOLUTIONS THAN THE ECMWF
MEMBERS.  WHEN THIS OCCURS...THE OPTIMAL LOCATION FOR LOW
PLACEMENT IS THE FAST SIDE OF THE ECMWF/SLOW SIDE OF THE GEFS
ENSEMBLE MEMBER SPREAD. THIS COMPROMISE WAS USED AS THE BASELINE
FOR THE PRESSURES.  SMALL REFINEMENTS WERE MADE PER THE ENSEMBLE
GUIDANCE AS WELL AS TO TIGHTEN UP PRESSURE/WIND GRADIENTS.  THE
POTENTIAL EAST COAST SYSTEM PORTENDS MORE SNOW TO THE MID-ATLANTIC
AND NEW ENGLAND STATES THU/FRI. THE GENERAL LARGE SCALE FLOW
PATTERN SURROUNDING ITS EVOLUTION AND STEERING SHOWS SOME
RESEMBLANCE TO THE LAST SNOWSTORM IMPACTING THE REGION JUST OVER A
WEEK AGO.

THE 06Z/27 GFS IS DROPPING  A STRONG PIECE OF ARCTIC ENERGY WELL S
INTO THE UPPER OH VLY BY DAY 6 SAT.  IF CORRECT...THIS UPPER
FEATURE COULD BE STRONG ENOUGH TO INDUCE COLD AIR DEVELOPMENT
BEHIND THE MAIN SYS WHICH WILL ALREADY BE OFFSHORE EARLY IN THE
WEEKEND....REJUVENATING SNOWFALL OVER NEW ENG.  THE 06Z/27 GFS RUN
IS A WESTERN OUTLIER WITH THE ARCTIC ENERGY...BUT IS JUST A BIT W
OF THE ECMWF WITH THE SAME FEATURE. WE WILL WATCH THIS EVOLUTION
OF THIS ARCTIC SYS ON NEW 12Z MODEL RUNS.  ENSEMBLE SPAGHETTI
PLOTS FAVOR A LESS AMPLIFIED  MORE PROGRESSIVE SOLUTION TO THIS
UPPER FEATURE NEXT WEEKEND.    

IN THE WEST...CONFIDENCE IS LOWEST IN THE EXPECTED FLOW PATTERN
NEXT WEEKEND AS THE DETERMINISTIC GUIDANCE SHOWS TROUGHING INTO
THE REGION WHICH IS SOMEWHAT OUT OF SYNC WITH THE 00Z GEFS/12Z
ECMWF ENSEMBLE MEANS WHICH SHOW FLAT FLOW OR WEAK RIDGING ACROSS
THE NORTHWEST AND SOUTHWEST CANADA.

ROTH/FLOOD



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Another Major Northeast snowstorm? - Fred, 12/26/2009, 1:37 pm
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