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FXUS02 KWBC 121805
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
205 PM EDT SAT SEP 12 2009
VALID 12Z TUE SEP 15 2009 - 12Z SAT SEP 19 2009
OPERATIONAL AND ENSEMBLE GUIDANCE SHOWS BETTER THAN AVERAGE
AGREEMENT WITH LARGE SCALE FLOW FOR THE MEDIUM RANGE FCST. DURING
THE FIRST TWO THIRDS OF THE PERIOD MULTI-DAY MEANS DERIVED FROM
LATEST AND RECENT SOLNS SHOW A STRONG NEGATIVE HGT ANOMALY CENTER
OVER THE NERN PACIFIC AND POSITIVE HGT ANOMALY CENTER CLOSE TO THE
SWRN SHORE OF HUDSON BAY. BY THE D+8 TIME FRAME THERE ARE
INDICATIONS THAT THE POSITIVE CENTER OVER CANADA MAY WEAKEN
SOMEWHAT ALONG WITH SOME SWWD ELONGATION OF THE OVERALL AREA OF
POSITIVE ANOMALIES AS HGTS RISE OVER THE WRN CONUS AND FAST
PACIFIC FLOW REACHES WRN CANADA.
THE AFOREMENTIONED LARGE SCALE FLOW FAVORS A MEAN TROF OVER ERN
CANADA AND NERN CONUS. WITHIN THIS FEATURE... LATEST SOLNS APPEAR
TO DISPLAY SOMEWHAT BETTER AGREEMENT WITH THE SERIES OF TWO
INDIVIDUAL TROFS EXPECTED DURING THE PERIOD. THE GFS IS ON THE
FAST EDGE OF GUIDANCE WITH THE FIRST TROF LATE IN THE SHORT RANGE
PERIOD... IS FAIRLY AGGRESSIVE IN CLOSING OFF ENERGY TO THE E OF
THE NEW ENGLAND COAST BY DAY 5 EARLY THU... AND IS SLIGHTLY SLOWER
THAN THE ECMWF/UKMET/CMC WITH THE SECOND TROF CONSISTING OF THE
COMBINATION OF NRN CANADA FLOW AND INITIAL CLOSED LOW ENERGY OVER
SRN CANADA. THE GFS TIMING OF THE SECOND TROF IS WITHIN THE 00Z
GEFS/12Z ECMWF ENSEMBLE SPREAD THOUGH. EXPECT WEAK FLOW OVER MOST
REMAINING AREAS OF THE CONUS. AS A RESULT EXPECT VERY SLOW
MOVEMENT OF AN ILL-DEFINED PLAINS/MS VALLEY UPPER LOW AND CNTRL
GULF COAST SFC LOW... WHILE MODEL CONSENSUS ANTICIPATES ONLY
GRADUAL SEWD PROGRESS OF A WEAK UPPER LOW OVER THE INTERIOR WEST.
MODEL/ENSEMBLE CONSENSUS RECOMMENDS LESS NWD ELONGATION OF THE MS
VALLEY SYSTEM THAN FCST BY THE GFS. FINALLY THERE ARE TYPICAL
DETAIL DIFFS WITHIN THE FAST FLOW FROM THE PAC INTO WRN CANADA
LATER IN THE PERIOD BUT OVERALL MODELS AND ENSEMBLES DISPLAY VERY
GOOD AGREEMENT.
BASED ON GUIDANCE CONSENSUS INDICATING THAT THE 00Z GFS MAY BE ONE
OF THE LESS LIKELY SOLNS WITH SOME ASPECTS OF THE DAYS 3-7 FCST...
EARLY PRELIM FRONTS/PRESSURES FOLLOW A BLEND OF 00Z ECMWF/00Z GEFS
MEAN/12Z ECMWF ENSEMBLE MEAN SOLNS. DAYS 3-4 TUE-WED GENERALLY
LEAN CLOSER TO THE OPERATIONAL ECMWF WHILE ITS WEIGHTING IS
REDUCED TO HALF FOR DAYS 5-7 THU-SAT AS CONFIDENCE IN SPECIFIC
DETAILS DECREASES.
UPDATED PRELIMS INCORPORATE THE USE OF THE 00Z ECMWF ENS MEANS TO
AN INCREASING DEGREE THRU THE PERIOD FOR SIMPLIFICATION. THIS
RESULTS IN A NEARLY TRANSPARENT CHANGE FROM PRIOR PROGS AT THE SFC
AND ONLY MINOR MID LEVEL CHANGES.
06Z/12Z GFS BOTH BY DAYS 6-7 HOLD WESTWARD THE ERN THIRD OF CONUS
TROF WITH INCREASED SWRLY MID LEVEL FLOW ALLOWING FOR EJECTION OF
THE MID LEVEL ENERGY AND A SFC LOW INTO THE UPPER OH VALLEY DAY 6
AND NEW ENG DAY 7 WITH SOME SUPPORT FROM THE 12Z GFS ENS MEANS.
THIS GOES AGAINST THE 00Z ECMWF AND ITS ENS MEAN ALONG WITH THE
00Z CMC AND UKMET RUNS. 12Z UKMET LIFTS THE GULF LOW NWD INTO IL
BY FRI WELL WESTWARD OF THE GFS SOLUTION. WILL ONLY HAVE SLIGHT
ADJUSTMENT TO DAY 6 FRI WITH ADDITIONAL AMPLITUDE TO THE SFC
INVERTED TROF ALLOWING MOISTURE TO POTENTIALLY SPREAD FARTHER NWD
AHEAD OF THE NEXT COLD FRONT AND HIGH PRESSURE SYSTEM COMING SEWD
OVER NEW ENG DAY 7.
RAUSCH/ROSENSTEIN
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