072
FXUS02 KWBC 201810
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
209 PM EDT SUN JUL 20 2008
VALID 12Z WED JUL 23 2008 - 12Z SUN JUL 27 2008
THE NATIONAL HURRICANE CENTER IS NOW PROVIDING OFFICIAL FORECAST
POINTS FOR NEW TROPICAL STORM DOLLY THAT IS EXPECTED TO INTENSIFY
WHILE TRACKING FROM THE WRN CARRIBEAN THROUGH THE YUCATAN THEN SRN
GULF OF MEX OVER THE NEXT SEVERAL DAYS...POTENTIALLY ON TRACK
TOWARD A VERY WET AND ROUGH LANDFALL IN THE VICINITY OF SRN TX/NRN
MEXICO WED. PLEASE REFER TO THE LATEST ADVISORIES FROM TPC/NHC
FOR UPDATED INFORMATION ON THIS VERY IMPORTANT SYSTEM.
MODEL AND ENSEMBLE GUIDANCE CONTINUES TO SHOW SIMILAR IDEAS
REGARDING THE LARGE SCALE FLOW BUT OFFER SOME MID-SMALLER SCALE
DIFFERENCES WITHIN THE OVERALL FULL ENVELOPE OF SOLUTIONS. A MEAN
TROF SHOULD PREVAIL OVER THE NERN PACIFIC/NWRN NORTH AMERICA...
WITH THE MEAN RIDGE OVER THE CNTRL OR W-CNTRL CONUS AMPLIFYING
INCREASINGLY NWD OVER CANADA WITH TIME. THE MEAN TROF OVER ERN
NOAM SHOULD PERSIST WITH ONE BUNDLE OF MID-LEVEL ENERGY LIFTING
OUT EARLY IN THE PERIOD...ONLY TO BE REPLACED BY AN UPSTREAM
SYSTEM BY NEXT WEEKEND.
THE 00Z ECMWF/CANADIAN MAINTAIN ENOUGH CONTINUITY TO MERIT SOME
ATTENTION WITH THEIR CONSOLIDATION OF ENERGY OVER CENTRAL PARTS OF
SRN CANADA AND SUBSEQUENT TRACK INTO THE ERN NOAM MEAN TROF.
CONFIDENCE INITIALLY WAS LOW THAT THE RESULTING SYSTEM WILL BE AS
STRONG AS DEPICTED IN EC/CMC...BUT HAS BEEN BOLSTERED AS THE 06/12
UTC GFS AND 12 UTC GFS ENSEMBLE MEAN HAVE TRENDING SIGNIFICANTLY
MORE TOWARD THAT TYPE OF SOLUTION. THIS ADJUSTMENT FROM PRELIM
GUIDANCE OPENS THE DOOR FOR A PATTERN WITH MORE LINGERING ERN NOAM
HEAVIER RAINFALL AND COOLING. MEANWHILE...THE 00 UTC GFS AND TO A
LESSER EXTENT GEFS MEAN MAY STILL BE A LITTLE AGGRESSIVE IN
BRINGING HEIGHT FALLS ACROSS HUDSON BAY ON DAY 4 THU AS TRENDS
HAVE GENERALLY FAVORED KEEPING HIGHER HEIGHTS OVER THAT REGION.
THUS...THE 00 UTC GFS/GEFS MEAN SEEM TOO FAST WITH THE NEWD
EJECTION OF INITIAL ERN NOAM TROF ENERGY.
THE OTHER SIGNIFICANT FORECAST ISSUE INVOLVES TO WHAT EXTENT NERN
PAC ENERGY PROGRESSES INTO WRN CANADA BY NEXT WEEKEND...WHICH
INFLUENCES THE EWD PROGRESSION OF A SFC FRONT THAT SHOULD EXTEND
INTO THE NWRN CONUS. OVER THE PAST DAY OR SO GUIDANCE HAS BEEN
PROVIDING MIXED MESSAGES WITH THE 00Z GFS AND RECENT ECMWF
ENSEMBLE MEANS SHOWING MORE EROSION OF THE CENTRAL CANADA RIDGE
VERSUS OTHER GUIDANCE BY DAY 7 SUN. STRENGTH OF THE RIDGE PRIOR
TO DAY 7 AND TYPICAL MODEL BIASES TOWARD WEAKENING RIDGES TOO
QUICKLY FAVOR LEANING AWAY FROM THE 00 UTC GFS AND ECMWF ENSEMBLE
MEANS.
ABOVE CONSIDERATIONS SUGGEST THAT WITHIN THE FULL ENVELOPE OF
POSSIBILITIES...THE DAYS 3-7 WED-SUN FORECAST WAS MAINLY DERIVED
FROM A 50-50 BLEND OF THE 00 UTC ECMWF AND THE 12 UTC GFS ENSEMBLE
MEAN TO ADDRESS UNCERTAINTY. THIS SOLUTION MAINTAINS GOOD
CONTINUITY WITH HPC PRELIM GUIDANCE OVERALL...BUT DOES ALLOW FOR A
SOMEWHAT MORE AMPLIFIED AND SLOWER MOVING ERN NOAM TROF LATE WEEK
INTO NEXT WEEKEND AND ADDS THE TPC FORECAST TRACK FOR NEW TS
DOLLY.
RAUSCH/SCHICHTEL
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