384
FXUS02 KWBC 261731
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
130 PM EDT SAT SEP 26 2009
VALID 12Z TUE SEP 29 2009 - 12Z SAT OCT 03 2009
MODELS AND ENSEMBLES AGREE THAT THE LONGWAVE FLOW FROM THE PACIFIC
ACROSS NORTH AMERICA AMPLIFIES SIGNIFICANTLY BY DAYS 4-7...AND
BECOMES LESS PROGRESSIVE WITH TIME AS BLOCKY CONDITIONS GRADUALLY
BUILD FROM THE NW ATLANTIC ACROSS NE CANADA. IN THIS PATTERN...AN
AMPLIFIED AND REINFORCED/COOLING MID-UPPER LEVEL TROUGH WILL
STRUGGLE TO EJECT FROM THE NERN US ACROSS THE CANADIAN MARITIMES.
THIS OCCURS EVEN AS ANOTHER DEEP AND GRADUALLY NEG-TILT MID-UPPER
LEVEL TROUGH AND DYNAMIC EMBEDDED FEATURES/LEAD SENSIBLE WEATHER
FOCUS ARE KICKED FROM THE WRN TO EAST-CENTRAL US DAYS 4-7 WITH
APPROACH OF NEW UPSTREAM PACIFIC ENERGIES. THIS LEADS TO SHARPER
WAVELENGTH SPACING ACROSS NOAM INTO DAYS 6/7 AS THE FEATURES BUMP
INTO THE EMERGING DOWNSTREAM BLOCKY PATTERN. THIS INTRODUCES
GREATER POTENTIAL FOR FORECAST ERROR. THE GOOD NEWS IS THAT HIGH
RESOLUTION GUIDANCE FROM THE 00 UTC ECMWF/ECMWF ENSEMBLES AND THE
00/06 UTC GFS RUNS ARE IN UNUSUALLY CLOSE AGREEMENT EVEN INTO DAYS
6/7 FROM THE PACIFIC ACROSS NOAM. THEY ALSO OFFER DECENT
CONTINUITY FROM THEIR RESPECTIVE 00 UTC GUIDANCE FROM
YESTERDAY...WITH THE ECMWF AND GFS RUNS MERGING UPON THIS MORE
COMMON SOLUTION. UNFORTUNATELY...CONTINUITY IS NOT AS PRONOUNCED
COMPARED TO THEIR RESPECTIVE 12 UTC RUNS FROM YESTERDAY NOR FROM
LOWER RESOLUTION 00 UTC GFS/CANADIAN/NAEFS ENSEMBLE GUIDANCE THAT
BECOMES INCREASINGLY OUT OF PHASE FROM THE ERN PAC INTO THE WRN US
DAYS 6/7.
HPC FINAL MEDIUM RANGE PROGS REMAIN PRIMARILY DERIVED FROM A 50-50
BLEND OF SIMILAR AND SEEMINGLY REASONABLE 00 UTC GFS/ECMWF
SOLUTIONS INTO THU. HOWEVER...PREFER TO INCORPORATE ABOUT A THIRD
OF 00 UTC ECMWF ENSEMBLE GUIDANCE INTO THE 00 UTC GFS/ECMWF MIX BY
NEXT THU/FRI TO INCREASINGLY WEED OUT LESS PREDICTABLE SMALLER
SCALE SOLUTION DIFFERENCES AND INTENSIFICATIONS AMID GROWING
UNCERTAINTY AND RUN TO RUN CONTINUITY CONCERNS. THIS HPC BLEND
MAINTAINS CLOSE HPC CONTINUITY AND FAVORS THE HIGHER RESOLUTION
GUIDANCE CLUSTER THAT IS ALSO WELL SUPPORTED BY THE LATEST 12 UTC
GFS.
SCHICHTEL
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