755
FXUS02 KWBC 011829
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
228 PM EDT TUE SEP 01 2009
VALID 12Z FRI SEP 04 2009 - 12Z TUE SEP 08 2009
MULTI-DAY MEANS OVER THE COURSE OF THE MEDIUM RANGE PERIOD DEPICT
A GRADUAL EWD PROGRESSION OF A NERN PAC TROF INTO WRN NOAM... WITH
SIMILAR MOVEMENT OF A DOWNSTREAM RIDGE ACROSS CNTRL CANADA. THIS
EVOLUTION WILL EVENTUALLY SERVE TO WEAKEN/DISPLACE A BROAD BUT
MODEST TROF FCST OVER THE E-CNTRL CONUS AS OF DAY 3 FRI. BY D+8
THERE IS REASONABLE AGREEMENT THAT THE DOMINANT ANOMALY CENTER
AFFECTING NOAM SHOULD BE OF THE POSITIVE VARIETY AND POSITIONED
NEAR SRN HUDSON BAY.
BY DAY 4 SAT THE 00Z ECMWF AND ECMWF ENSEMBLE MEAN ARE SLOWER THAN
MOST OTHER 00Z MODEL/ENSEMBLE GUIDANCE WITH THE NERN PAC TROF
EDGING TOWARD WRN NOAM. THE 06Z GFS AND TO A LESSER EXTENT 00Z
GFS BECOME SOMEWHAT FASTER THAN THE 00Z GEFS MEAN AND MOST OTHER
SOLNS WITH UPSTREAM NRN PAC FLOW FROM DAY 4 ONWARD... BUT WITH THE
00Z UKMET/CMC FASTER THAN THE 00Z ECMWF IT SEEMS REASONABLE TO
FOLLOW AT LEAST A COMPROMISE BETWEEN THE 00Z ECMWF AND SOMEWHAT
FASTER 12Z/31 ECMWF RUN THRU DAY 4. BY THE LATTER HALF OF THE
PERIOD THE 00Z ECMWF/EC ENSMEAN COULD STILL BE A LITTLE SLOW BUT
THE FAIRLY CONSISTENT GEFS MEAN AND OTHER SOLNS FORM A SOLID
CONSENSUS THAT IS SLOWER THAN OPERATIONAL GFS RUNS... ESPECIALLY
THE 06Z VERSION. FARTHER EWD... DURING THE FIRST HALF OF THE
PERIOD THE 00Z GFS DOES NOT COMPARE WELL TO OTHER MODELS WITH THE
AMOUNT OF ENERGY PASSING OVER THE OH VALLEY/NRN APLCHNS. THE 06Z
GFS PROVIDES AN IMPROVED SOLN IN THIS REGARD. BY THE LATTER HALF
OF THE FCST PERIOD THE OVERWHELMING MAJORITY OF 00Z GEFS/ECMWF
ENSEMBLES WOULD SUGGEST THE 00Z ECMWF BECOMES TOO SLOW/SHARP WITH
THE CNTRL CANADA RIDGE AND TOO DEEP/AMPLIFIED WITH THE TROF THAT
DEVELOPS OVER ERN CANADA.
CONSULT LATEST TPC DISCUSSIONS/ADVISORIES FOR FURTHER INFO
REGARDING ERN PAC HURCN JIMENA. THE 15Z TPC ADVISORY ANTICIPATES
A TRACK ACROSS BAJA CALIF WITH THE SYSTEM EVENTUALLY WEAKENING TO
A TROPICAL DEPRESSION BY THE TIME IT APPROACHES THE SRN AZ BORDER
BY EARLY SUN. MEANWHILE THE 00Z CANADIAN IS A FAST/STRONG OUTLIER
WITH ITS TROPICAL SYSTEM THAT TRACKS TO THE MID ATLC COAST.
VERIFICATION THUS FAR THIS SEASON DOES NOT FAVOR THE CMC SOLN.
THERE IS STILL CONSIDERABLE SPREAD AMONG REMAINING SOLNS... WITH
16Z TPC/HPC COORDINATION YIELDING A MERE TROF APPROACHING THE SERN
COAST BY DAY 7 TUE BASED ON POTENTIAL FOR AN UNFAVORABLE
ENVIRONMENT FOR DEVELOPMENT BY THE LATTER HALF OF THE FCST PERIOD.
THE UPDATED PRELIM FCST FOR DAYS 3-4 FRI-SAT STARTED WITH A BLEND
OF 00Z AND 12Z/31 ECMWF RUNS TO RESOLVE THE TIMING DIFFS WITH THE
NERN PAC TROF NEARING THE WEST COAST... AND TO ACCOMMODATE THE
NON-00Z GFS CONSENSUS WITH FEATURES OVER THE ERN HALF OF THE
CONUS. DAYS 5-7 SUN-TUE FOLLOWED A BLEND OF HALF 12Z/31 ECMWF AND
THE REMAINDER 00Z GEFS/ECMWF ENSEMBLE MEANS TO INCORPORATE THE
BEST CLUSTERING OF GUIDANCE WITH THE TROF ENTERING WRN NOAM AND
FLOW ACROSS ERN NOAM.
12Z UPDATE... THE NEW GFS HAS TRENDED SLOWER THAN 06Z/00Z RUNS
WITH THE ERN PAC TROF MOVING INTO WRN NOAM. THE 12Z UKMET BECOMES
THE EXTREME SOLN ON THE FAST SIDE OF THE SPREAD BY SUN-MON...
WHILE THE 12Z GEFS MEAN AND CMC STILL FAVOR SOMEWHAT FASTER TIMING
THAN THE 00Z ECMWF. MEANWHILE THERE IS STILL DECENT UNCERTAINTY
WITH HOW MUCH TROFFING WILL EVOLVE OVER ERN CANADA/NEW ENGLAND BY
SUN-TUE. AT THE VERY LEAST IT APPEARS THE 12Z GFS MAY BE A LITTLE
TOO FAST AND/OR AMPLIFIED WITH ITS SHRTWV THAT REACHES NEW ENGLAND
ON MON. WITH REASONABLE SUPPORT FOR PRIOR REASONING... THE FINAL
FCST MAINTAINS GOOD CONTINUITY FROM THE UPDATED PRELIM ISSUANCE.
REGIONAL HIGHLIGHTS...
..WEST
AREAS FROM THE SOUTHWEST INTO THE CNTRL-SRN ROCKIES SHOULD SEE
UNSETTLED CONDS WITH NEAR TO BELOW NORMAL DAYTIME TEMPS. RNFL AT
SOME LOCATIONS MAY BE ENHANCED BY MOISTURE FROM ERN PAC HURCN
JIMENA. CONSULT TPC DISCUSSIONS/ADVISORIES FOR LATEST INFO
REGARDING JIMENA. OVER THE NRN HALF OF THE WEST... EXPECT AN
INCREASE IN MOISTURE AND DECREASE IN TEMPS FROM WEST TO EAST AS A
NERN PAC FRONT CROSSES THE REGION DURING THE WEEKEND.
..CENTRAL/EAST
WEAK MID LVL ENERGY CENTERED OVER E-CNTRL CONUS AS OF LATE THIS
WEEK MAY ENHANCE CONVECTION OVER PORTIONS OF THE ERN PLAINS/MS
VALLEY AND VICINITY LATE THIS WEEK INTO THE WEEKEND. BEHIND THIS
AREA OF ACTIVITY... COMBINATION OF SWRN CONUS/ROCKIES MOISTURE AND
SYSTEM CROSSING THE NRN HALF OF THE WEST WILL LIKELY INCREASE THE
COVERAGE AND INTENSITY OF RNFL/TSTMS OVER THE PLAINS FROM THE
WEEKEND INTO EARLY NEXT WEEK. EXPECT DIURNALLY ENHANCED ACTIVITY
ALONG THE GULF/SERN COASTS... WITH MOISTURE FROM AN AREA OF
DISTURBED WEATHER OVER THE ATLC ALSO POSSIBLY APPROACHING THE SERN
COAST DURING THE FIRST HALF OF NEXT WEEK. EXPECT TEMPS TO BE
ABOVE NORMAL OVER THE NRN TIER AND CLOSER TO NORMAL SOUTH.
MULTIPLE DAYS OF MUCH ABOVE NORMAL READINGS ARE POSSIBLE OVER THE
EXTREME NRN PLAINS.
RAUSCH/CISCO
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