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FXUS02 KWBC 271852
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
252 PM EDT SUN SEP 27 2009
VALID 12Z WED SEP 30 2009 - 12Z SUN OCT 04 2009
A PATTERN RESEMBLING LATER IN THE FALL WILL BE FEATURED DURING THE
MED RANGE FCST PERIOD. A LARGE CLOSED LOW STARTING OFF OVER ERN
CANADA WILL MOVE LITTLE DURING THE FCST PERIOD AS A LARGE ATLANTIC
RIDGE WILL BLOCK ITS PROGRESSION. THUS EXPECT THIS LOW OVER ERN
CANADA ON WED TO BASICALLY REFORM ACROSS NEW ENGLAND INTO NOVA
SCOTIA ON FRI AND COULD REMAIN PRESENT INTO NEXT WEEKEND...BUT THE
BULK OF LATEST 12 UTC GUIDANCE IS TRENDING TO ALLOW MORE OF A
PORTION OF THIS TROUGH TO EJECT SLOWLY OUT AS ANOTHER PORTION
RETROGRADES/PHASES BACK WITH TRAILING CLOSED SYSTEM ENERGY.
PREFER TO MAINTAIN HPC CONTINUITY WITH THE FINAL PROGS FOR NOW
WITH THIS COMPLEX SYSTEM.
MEANWHILE UPSTREAM...A SHARP AMPLIFIED UPPER TROUGH STARTING OFF
OVER THE WRN REGION ON WED WILL SPLIT AND THE POTENT SRN PORTION
OF THE TROUGH WILL EJECT OUT INTO THE PLAINS ON THURS. DUE TO THE
BLOCKING NATURE OF THE FLOW DOWNSTREAM...THIS CLOSED LOW FEATURE
WILL GRADUALLY LIFT NORTH AND EAST INTO THE UPR MS VLY WHILE GOING
NEGATIVE TILT. THE MODEL GUIDANCE... ESPECIALLY THE 00Z
GFS/ECMWF...IS IN REAL SOLID AGREEMENT INTO DAY 5/FRI. AFTER FRI
INTO D6 AND 7...MORE SPREAD EXISTS INCLUDING SOME POTENTIAL CLOSED
SYSTEM TRACK/PHASING ISSUES WITH E-CENTRAL AND NERN US SYSTEMS AS
MENTIONED ABOVE. THE MORE PHASED 00 UTC ECMWF SOLUTION IS NOW ALSO
SUPPORTED BY THE NEWER 12 UTC ECMWF/GFS/CANADIAN...BUT NOT THE 12
UTC UKMET. HPC FINAL PROGS STILL INCORPORATE FOR NOW IN THE FINAL
PROGS MORE OF THE PREVIOUS HPC IDEA THAT WAS MORE IN LINE WITH THE
00 UTC GFS...COMPATIBLE 12Z/26 ECMWF...AND ENSEMBLE MEANS BUT
FORECASTER CONFIDENCE HAS DECREASED.
MEANWHILE...REPLACING THE SYSTEM OVER THE WEST WILL BE ANOTHER
DIGGING SHORT WAVE FROM THE NERN PAC... WHICH SHOULD ARRIVE INTO
THE NW LATE FRI/SAT AND CLOSE OFF ANOTHER SIGNIFICANT CLOSED LOW.
DESPITE SOME SMALLER SCALE/INTENSITY DIFFERENCES WITH THIS
SUBSEQUENT WRN LOW FROM ALL GUIDANCE...THE 00 UTC GFS/ECMWF AND
ECMWF ENSEMBLES REMAIN IN UNUSUALLY GOOD AGREEMENT EVEN INTO DAYS
6/7 FROM THE PACIFIC INTO WRN NOAM. HOWEVER...CONTINUITY IS NOT
AS PRONOUNCED COMPARED TO LOWER RESOLUTION 00 UTC
GFS/CANADIAN/NAEFS ENSEMBLE GUIDANCE THAT BECOMES OUT OF PHASE
ACROSS THE ERN PAC THU/FRI LEADING TO A LESS AMPLIFIED WRN US
MID-UPPER LEVEL SYSTEM OVER THE WRN US NEXT WEEKEND. PREFER TO
HOLD HPC CONTINUITY WITH A MORE AMPLIFIED SOLUTION CLOSER TO THE
HIGHER RESOLUTION GUIDANCE CONSIDERING UPSTREAM RIDGE AMPLITUDE
POTENTIAL.
MUSHER/SCHICHTEL
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