Possible Nor'easter & Negative-Tilted Shortwave Combo early next week
Posted by JAC on 11/19/2009, 7:11 am
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
329 AM EST THU NOV 19 2009

VALID 12Z MON NOV 23 2009 - 12Z THU NOV 26 2009

THE MODELS HAVE BEEN STRUGGLING TO TRACK THE STRENGTH AND TIMING
OF THE PACIFIC FEATURES PROGRESSING INTO NORTH AMERICA DURING THE
MEDIUM RANGE PERIOD.  THE GENERAL CONSENSUS SUPPORTS A SHARP
TROUGH AMPLIFYING OVER THE PLAINS BY DAY 4 AND EVOLVING INTO A
SLOW MOVING CLOSED LOW PUSHING NORTHEASTWARD THEREAFTER.  THE 00Z
MODELS INDICATE LARGE DIFFS AND POOR CONTINUITY WITH THE DETAILS
OF THIS SYSTEM.  CONFIDENCE IS THEREFORE BELOW AVERAGE WITH THE
SYNOPTIC PATTERN...ESPECIALLY ON DAYS 6 AND 7.  LEANED TOWARD THE
ECMWF SOLN WHICH HAS SOME SUPPORT FROM THE GLOBAL ENS MEAN IN
DISPLAYING A LONGWAVE TROUGH SETTLING INTO THE MIDWEST AND A SFC
FRONT PUSHING TO THE EAST COAST TOWARD THE END OF THIS PERIOD.

UNCERTAINTY ALSO PERSISTS WITH THE FEATURE REACHING FROM THE GULF
COAST TO THE EASTERN SEABOARD ON DAYS 4 AND 5.  THE GFS REMAINS
THE STRONGEST AND HAS THE FARTHEST NW TRACK INTO THE NORTHEAST.
THE ECMWF IS REASONABLY CONSISTENT WITH A MORE OFFSHORE TRACK AND
WAS MOSTLY FOLLOWED.  
THE 00Z MODELS ARE IN GENERAL AGREEMENT ALONG THE WEST COAST WHERE
AN UPPER RIDGE POSITION IS FORECAST TO ALIGN AS THE PACIFIC JET
RETREATS NORTHWARD.  

HEDGE





EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
234 PM EST WED NOV 18 2009

VALID 12Z SAT NOV 21 2009 - 12Z WED NOV 25 2009


EXPECT AN ACTIVE PROGRESSIVE PATTERN ACROSS THE COUNTRY DURING
THIS MEDIUM RANGE PERIOD AS A MAJOR TROF PUSHES INTO THE WRN
STATES DAY 3 SAT. AS THIS TROF PUSHES EWD...IT WILL SCOOP UP
LEFTOVER SRN STREAM ENERGY THAT MAY SUPPORT ANOTHER SYS MOVING
NEWD ALONG THE S ATLANTIC COAST EARLY NEXT WEEK. BY TUE-WED DAYS
6-7...THE ERSTWHILE MAJOR WRN TROF MAY PROGRESS IN THE E CENTRAL
STATES....WITH PLENTY OF ENERGY IN THE SRN PORTION OF THE TROF.

BY THAT TIME...00Z/18 ENSEMBLE SPAGHETTI PLOTS SHOWED THAT GEFS
ENSEMBLE MEMBERS WERE A DAY FASTER WITH THE EWD TRANSLATION OF THE
TROF THAN CORRESPONDING ECMWF ENSEMBLE MEMBERS. THE DETERMINISTIC
00Z/18 ECMWF WAS AMONG THE SLOWEST SOLUTIONS WITH TRANSLATION OF
THIS TROF BY TUE-WED DAYS 6-7. FOR OUR FINALS...WE KEPT OUR BLEND
OF 50% CANADIAN AND 50% ECMWF ENSEMBLE MEAN. HOWEVER...WE SLOWED
DOWN THE WAVY FRONTAL SYS MOVING INTO THE ERN STATES TO GET CLOSER
TO THE CONSENSUS OF NEW 12Z/18 DETERMINISTIC MODELS ON THE TIMING
OF THE ASSOCIATED UPPER TROF.

IN THE WAKE OF THE PROGRESSIVE TROF CROSSING THE CONUS...UPPER
RIDGING SHOULD BUILD INTO THE  WRN STATES...BUT FAIRLY FAST FLOW
FROM THE PACIFIC WILL TOP THE NRN PORTION OF THIS RIDGE. THE
RESULT WILL BE A SERIES OF SHORTWAVES IN THE FAST FLOW THAT WILL
DEPOSIT MOST OF THIER MOISTURE ON THE COASTAL AND CASCADE RANGES
OF THE PACIFIC NW...WITH LIGHTER AMOUNTS INLAND ALONG THE NRN
CONTINENTAL DIVIDE.  

THE JURY IS STILL OUT ON HOW MUCH OF A SYS MIGHT MOVE UP THE E
COAST SUN-MON DAYS 4-5...DEPENDING ON HOW WELL SRN STREAM ENERGY
HOLDS TOGETHER. COMPLICATING THE BEHAVIOR OF THE NEXT E COAST SYS
WILL BE THE INTERACTION OF A MID LATITUDE SHORTWAVE IN THE WAKE OF
THE DEPARTING CLOSED LOW NOW CROSSING THE SRN GRT LAKES REGION
WITH ANOTHER SHORTWAVE RAPIDLY CROSSING THE SRN BORDER OF THE
LOWER 48. MODELS/ENSEMBLES DO NOT FAVOR PHASING THESE TWO
SYS...WHICH WILL LIMIT THE NRN EXTENT OF THE PCPN ASSOCIATED WITH
THE SURFACE DEVELOPMENT MON.  THE 12Z GFS/ECMWF WOULD LIMIT THE
NRN EXTENT OF THE PRECIP INTO THE MID ATLANTIC WHILE THE CANADIAN
UKMET SUN WOULD ALLOW IT TO COME FARTHER N.  


CONCERNING THOSE 12Z/18 DETERMINISTIC MODELS...THE CANADIAN
DEFINED THE SLOW SIDE OF THE SOLUTION ENVELOPE WITH THE NEXT MAJOR
UPPER TROF FOR MON-TUE DAYS 5-6 WHILE THE GFS DEFINED THE FAST
SIDE. THE NEW ECMWF REALLY SLOWED DOWN ON DAY 7 WITH ITS CUTOFF
LOW OVER THE OK PANHANDLE. IT LOOKS TOO SLOW...BUT AS A
PRECEDENT...WE ARE STILL DEALING WITH A MS VLY CUTOFF THAT HAS
TAKEN ITS SWEET TIME TO BEGIN MOVING OUT.  


FLOOD


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Possible Nor'easter & Negative-Tilted Shortwave Combo early next week - JAC, 11/19/2009, 7:11 am
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