187
FXUS02 KWBC 241808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
207 PM EDT THU JUL 24 2008
VALID 12Z SUN JUL 27 2008 - 12Z THU JUL 31 2008
WE STILL SEE NO STRONG COMPELLING REASON TO SIGNIFICANTLY ADJUST
HPC CONTINUITY WITH OUR FINAL MEDIUM RANGE GUIDANCE PACKAGE. THE
VAST BULK OF MODEL AND ENSEMBLE GUIDANCE STILL MAINTAIN AN
UNSEASONALLY AMPLIFIED MEAN PATTERN CONSISTING OF A NERN
PACIFIC/NWRN NORTH AMERICA TROF...W-CENTRAL CONUS/CENTRAL CANADA
RIDGE...AND ERN NOAM TROF THRU THE MEDIUM RANGE PERIOD. SIMILAR
LARGER SCALE GUIDANCE ONCE AGAIN ALLOWS/POINTS TO PREFERENCE
TOWARD A CLUSTERED/CONSENSUS FORECAST METHODOLOGY WITHIN THE FULL
ARRAY OF SOLUTIONS THAT DOWNPLAY SEEMINGLY LOWER CONFIDENCE SMALL
SCALE DETAILS OF INDIVIDUAL MODELS AND ENSEMBLE MEMBERS.
ONE SIGNIFICANT QUESTION MARK IN THE FCST CONTINUES TO BE THE
EVOLUTION OF ENERGY THAT IS GENERALLY FCST TO TRAVEL FROM THE PAC
NW THRU THE MEAN RIDGE AND THEN AMPLIFY INTO ERN NOAM TROF. 00Z
GEFS ENSEMBLES INDICATE THE 00Z GFS AMPLIFICATION OVER THE UPPER
MS VALLEY/GREAT LAKES AND ASSOCIATED GREAT LAKES SURFACE LOW BY
DAYS 6-7 WED-THU SEEMS TOO FAR WWD CONSIDERING WAVELENGTH SPACING.
THAT SOLUTION HAS ONLY EXTREMELY LIMITED ENSEMBLE SUPPORT. THE
06 UTC AND NOW THE 12 UTC GFS HAVE TRENDED SIGNIFICANTLY AWAY FROM
THAT LOW BUT STILL HAVE A WAVY FRONT. IN CONTRAST TO THE 00 UTC
GFS SURFACE LOW...BY DAY 7 RECENT ECMWF/CMC ENSEMBLE MEANS AND
GEFS MEANS ALL SHOW HIGH PRESSURE OVER THE GREAT LAKES. THE 00Z
ECMWF CONFORMS SOMEWHAT BETTER TO CONSENSUS BUT COULD STILL BE A
TAD STRONG WITH ITS EVOLUTION...AND FOLLOWS AN OUTLIER 12Z/23
ECMWF RUN THAT WAS LIKELY TOO QUICK TO BRING TRAILING ENERGY INTO
WRN-CNTRL NOAM IN THIS TYPE OF AMPLIFIED FLOW. OVERALL...AN
ADJUSTMENT IN OUR FINAL PROGS WAS MADE TO HOLD THE FRONT A BIT
FARTHER NORTH THAN EARLIER GUIDANCE...RESPECTING THE TIME OF YEAR
AND AT LEAST POTENTIAL FOR FRONTAL WAVE DEVELOPMENT THAT IN
ADDITION TO THE FRONT WOULD ACT TO FOCUS WIDESPREAD HEAVY SUMMER
CONVECTION.
MEANWHILE MOST MODELS INDICATE FAIRLY SLOW MOTION OF MID LEVEL
ENERGY ORIGINALLY ASSOCIATED WITH DOLLY...WITH A GENERAL
TRAJECTORY AROUND A HIGH CENTER TO OVER OR NEAR THE S-CENTRAL RN
HIGH PLAINS BY THE BEGINNING OF NEXT WEEK. BASED ON THE ARRAY OF
00Z MODELS IT APPEARS THERE WILL BE A FINE LINE BETWEEN THIS
ENERGY REMAINING OVER THE PLAINS FOR MOST OF THE PERIOD OR BEING
PICKED UP BY NRN STREAM FLOW. THE EXACT TRACK/EMPHASIS REMAINS
DIFFICULT...BUT IT SHOULD ACT AS AN ACTIVE AND LOCALLY HEAVY
CONVECTIVE FOCUS.
A BLEND OF THE GFS/ECMWF RUNS SEEMS TO ACCOUNT FOR MOST MINOR
DIFFERENCES IN THE DAY 3 SUN FORECAST. FOR DAYS 4-7 MON-THU
THOUGH...PREFER A NEARLY EVEN BLEND OF THE 00Z GEFS MEAN... 00Z/24
ECMWF ENSEMBLE MEAN...AND 00Z ECMWF. THIS SOUTION EMPHASIZES THE
CONTINUED AGREEMENT UPON THE LARGE SCALE MEAN PATTERN AND FAVORED
FEATURE WITHIN...WHILE ALLOWING FOR THE MODEST CHANCE THAT NRN
STREAM ENERGY IN SOME FORM MAY SUPPORT A ORGANIZED AND PCPN
FOCUSING WAVE ALONG THE PERSISTENT CENTRAL-ERN CONUS FRONT
MID-LATER NEXT WEEK.
RAUSCH/SCHICHTEL
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