Prognostic Meteorological Discussion
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FXUS02 KWBC 221839
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
139 PM EST SUN NOV 22 2009

VALID 12Z WED NOV 25 2009 - 12Z SUN NOV 29 2009


THE ECMWF CONTINUES TO BE THE MOST CONSISTENT OF THE GLOBAL MODELS
WITH THE HANDLING OF THE UPCOMING PATTERN ACROSS THE NATION...SO
ONCE AGAIN RELIED HEAVILY ON ITS MASS FIELDS TO CONSTRUCT THE
PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7.  THE 00Z/22
DETERMINISTIC ECMWF IS A MORE AMPLIFIED VERSION OF THE 12Z/21 EC
ENSEMBLE MEAN...SO THE TWO BLENDED...PARTICULARLY AT THE LATER
TIME RANGES...SHOULD AFFORD A MORE STABLE FORECAST.  THE GFS...GEM
GLOBAL...AND UKMET CANNOT AGREE ON THE DEGREE OF AMPLIFICATION OF
THE CRITICAL WAVE OVER THE EAST BY DAYS 5 AND 6...SO ARE NOT
ESPECIALLY USEFUL FOR THIS FORECAST.

...UPDATED PRELIMS AND AFTN FINALS ARE BASED ON 00Z ECMWF DAYS 3
AND 4 AND ECMWF/GFS ENS MEANS DAYS 5-7.THERE IS GOOD MODEL
AGREEMENT DAYS 3 AND 4 WED/THU AS A CLOSED LOW MOVES NEWD IN THE
GREAT LAKES REGION WHILE A STRONG DIGGING SHORTWAVE DIVES SEWD
THRU THE DAKOTAS/CENTRAL PLAINS  AND RESULTS IN FORMING ANOTHER
STRONG CLOSED MID LEVEL LOW SYSTEM IN THE CENTRAL MS/LOWER OH
VALLEY REGION BY EARLY THURSDAY. THIS RESULTS IN RAINY CONDITIONS
ACROSS THE GREAT LAKES REGION WED WITH SNOW ACROSS THE ERN DAKOTAS
IN MN AND WRN WI. SNOW CONDITIONS WILL SPREAD SEWD ACROSS IA/IL
INTO IN/OH/KY AND NRN TN LATE THURSDAY AND INTO THE CENTRAL AND
PORTIONS OF SRN APPLCHNS LATE THURSDAY INTO EARLY FRIDAY. THERE IS
THE POTENTIAL FOR SOME POCKETS OF HEAVIER CONVECTIVE SNOWFALL AS
THE MID LEVEL CLOSES OFF IN THIS REGION.

DETAILS FOR DAYS 5-7 BECOME MORE DIFFICULT AND CONFIDENCE IS
LESSENED AS TO THE LOCATION AND TRACK OF A CLOSED OFF MID LEVEL
CENTER AS IT MOVES EAST AND NEWD THRU THE CENTRAL APPLCHNS AND
NEWD. OP MODELS 00Z/06Z GFS/UKMET/GFSP/ECMWF ALL HAVE A MORE SRLY
TRACK OF THE MID LEVEL CLOSED LOW THAN PRIOR RUNS WHILE CMC AND
ENS MEANS OF GFS AND ECWMF TAKE A MID LEVEL CENTER 200-250 NM
FARTHER NORTH. STRONG DYNAMICS/AND MID LEVEL COLD POOL WITH THE
CENTER INDICATE A THREAT OF CONVECTIVE SNOWFALL NEAR ITS TRACK.
THE SRN MOST SOLUTIONS ARE ACROSS VA AS FAR SOUTH AS THE NC BORDER
AND CONSIST OF 06Z GFS AND 00Z/06Z GFSP RUNS. LAGGED AVERAGE
FORECASTS OF THE PAST 4 RUNS OF GFS AND ECMWF ALONG WITH AN 8
MEMBER COMBINED LAGGED AVERAGE FORECAST OF THESE MODELS INDICATE A
MID LEVEL LOW CENTER FARTHER NWD OVER NY TO LAKE ERIE. THIS IS A
PREFERED HPC SOLUTION AT THIS TIME AND IS DEPICTED WELL BY GFS AND
ECMWF ENS MEANS. THIS RESULTS IN A SNOW THREAT ACROSS FRIDAY
ACROSS WRN PORTIONS OF PA/NY/ NWRN MTN PORTIONS OF WV/VA/MD AND
INTO WRN NEW ENG LATE FRI WITH RAIN ACROSS THE MID ATLC AND
NORTHEAST/NEW ENG COASTS. A MORE SWD TRACK OF THE MID LEVEL CENTER
WOULD SHIFT THE COLDER PCPN TYPE FARTHER SWD. DEEPENING SFC LOW
OFF THE NEW ENG COAST WILL BRING BREEZY CONDITIONS ACROSS MOST OF
THE EAST FROM GA NWD FRI AND SAT.

PARALLEL GFSP 00Z/06Z RUNS ARE VERY STRONG WITH THE MID LEVEL AND
HAVE THE SRN MOST TRACK OF ALL MODELS. SFC LOW INDICATING
PRESSURES AS LOW AS 975 MB OFF CAPE COD WITH INLAND HIGH WIND AND
COASTAL STORM CONDITIONS. 12Z GFSP IS WEAKER THAN PRIOR RUNS BUT
STILL THE FARTHEST SOUTH TRACK AND HAS RAISED ITS SFC PRESSURE
15MB OFF THE NEW COAST COMPARED TO ITS PRIOR RUN. THIS WILL BE A
GOOD TEST FOR THIS MODEL AS IT IS CURRENTLY EXPECTED TO REPLACE
THE CURRENT GFS MID DEC.

NEXT COLD PAC TROF MOVES TO THE WEST COAST LATE THURSDAY AND
FRIDAY AND EASTWARD TO THE ROCKIES SUNDAY. THERE ARE ENOUGH MODEL
DIFFERENCES TO PREFER A BLEND OF THE ENS MEANS OF BOTH GFS/AND
ECMWF TO RESOLVE THIS. COLD PAC HIGH PRESSURE SHOULD BUILD INTO
THE INTERMTN REGION WITH A POTENTIAL OFFSHORE/SANTA ANA EVENT OVER
THE WEST COAST

MOST 12Z GUIDANCE MODELS INDICATE A GENERAL TREND OF TAKING THE
MID LEVEL CLOSED LOW NWD OF THE 00Z/06Z TRACK RUNS WITH THE 12Z
GFSP NOW HAVING A SFC CENTER OFF THE NEW ENG COAST 15 MB HIGHER
THAN THE PRIOR RUNS. ECMWF REMANS SIMILR TO ITS FORMER 00Z RUN.
THE ONLY ADJUSTMENT MADE WILL BE FOR DAY 5 H500 PROGS SPEEDING UP
THE MID LEVEL CENTER TO THE ERN GREAT LAKES REGION.
CISCO/ROSENSTEIN
$$





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