281
FXUS02 KWBC 231741
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
117 PM EDT WED SEP 23 2009
VALID 12Z SAT SEP 26 2009 - 12Z WED SEP 30 2009
GLOBAL GUIDANCE HAS MAINTAINED GOOD CONSISTENCY WITH PRIOR RUNS
REGARDING THE SYNOPTIC PATTERN TO AFFECT THE CONUS DURING THE
MEDIUM RANGE PERIOD...WITH AMPLIFICATION OF THE LONGWAVE FLOW BUT
WITH DETAIL DIFFERENCES WITH THE SHORTWAVE PATTERN CONTINUING. THE
UPPER LOW OVER THE PLAINS ON DAY 3 WILL ACCELERATE EASTWARD IN
RESPONSE TO RAPID APPROACH OF A DIGGING SHORTWAVE TROUGH ACROSS
CANADA...WHICH EVOLVES INTO AN UPPER LOW OVER THE GREAT LAKES BY
DAY 5. THE SLOWER TREND NOTED IN GUIDANCE REGARDING THE UPPER LOW
OVER THE PLAINS FAVORS THE SLOWER SIDE OF THE GUIDANCE AS THE LOW
LIFTS INTO THE NORTHEAST DAYS 4/5...WHICH GENERALLY EXCLUDES THE
GFS. OTHERWISE THE MODELS ARE REASONABLY WELL CLUSTERED WITH THE
POSITIONING AND INTENSITY OF THE NEWLY FORMING UPPER LOW OVER THE
GREAT LAKES...WITH EITHER THE GFS/ECMWF BLENDED WITH THE GEFS MEAN
PREFERRED...VERSUS USING THE OLDER ECMWF ENSEMBLE MEAN WHICH IS
CONSIDERED TOO FAR NORTH WITH THE LOW DAYS 5/6. THE RESULT IS A
WEAKER VERSION OF THE GFS/ECMWF BUT SIMILARLY PLACED. ACROSS THE
WEST...THE GFS LIES NEAR THE FAST SIDE OF THE GUIDANCE WITH
INFLUENCE FROM AN AMPLIFYING LONGWAVE TROUGH OVER THE NORTHWEST
DAY 5...WITH DETERMINISTIC/ENSEMBLE GUIDANCE SUPPORTING THE NEW
ECMWF BLENDED WITH THE GEFS MEAN TO ACCOUNT FOR THE GROWING
SOLUTION SPREAD...ESPECIALLY BY DAYS 6/7.
UPDATED MORNING RE EVALUATION AND ADDITION OF 06Z GFS AND 00Z
ECMWF MEANS SHOWS OVER ALL GOOD MODEL AGREEMENT. AN UPDATED
PREFERENCE IS A 50/50 COMBINATION OF OP CMC AND ECMWFDAYS 3-5 AND
BLEND OF ENS MEANS OF GFS/ECMWF FOR DAYS 6 AND 7. THIS SOLUTION
SHOULD BE CLOSE TO MOS MOST AREAS.
12Z MODEL RUNS OF GFS SIMILAR TO THE PRECEDING RUN BUT WITH LESS
TROF AMPLITUDE OVER CA DAY 7 AND MORE IN LINE WITH CONSENSUS OF
ENS MEANS WITH UKMET AND CMC MAINTAINING CONTINUITY. NO CHANGES TO
AFTN FINALS FROM MORNING PRELIMS.
MDT/HEAVY FRONTAL RAINS SHOULD OCCUR WITH THE LEAD EXITING
SHORTWAVE DAYS 3-4 INTO THE UPPER OH VALLEY/APPLCHNS AMD THEN EWD
FROM NEW ENG SWD ALONG THE ATLC SEABOARD INTO NRN FL AS THE FRONT
MOVES OFFSHORE. STRONG COLD FRONT WILL PUSH SWD OVER THE NRN
PLAINS SUN AS THE NEXT DIGGING SHORTWAVE DROPS SEWD AND DEVELOPS
AN INTENSE STORM OVER LK SUPERIOR BY MONDAY WITH HIGH WINDS MON
AND TUES OVER THE UPPER MS VALLEY AND WRN GREAT LAKES WITH HVY
RAINFALL POTENTIAL MON. HIGH CONFIDENCE WITH THIS EVENT AS ALL OP
MODELS AND ENSEMBLES TARGET THIS AREA AND WITH INTENSITY. NEXT PAC
TROF WILL BRING IN COOLER TEMPS TO THE WEST WITH RAIN OVER THE PAC
NORTHWEST AND NRN CA COASTAL REGION WED.
JAMES/ROSENSTEIN
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