735
FXUS02 KWBC 261853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
251 PM EDT THU JUN 26 2008
VALID 12Z SUN JUN 29 2008 - 12Z THU JUL 03 2008
PRELIMINARY UPDATE...
MEDIUM RANGE GUIDANCE SHOWS BETTER THAN AVERAGE AGREEMENT
REGARDING THE LARGE SCALE MEAN FLOW DURING THE PERIOD. AN
AMPLIFYING ERN PACIFIC TROF SHOULD KICK OUT CLOSED LOW ENERGY FCST
TO BE OFF THE CA COAST AS OF DAY 3 SUN. MEANWHILE FLOW ENTERING
WRN CANADA EARLY IN THE PERIOD SHOULD GENERALLY PROGRESS E/SE TO
YIELD A DAYS 7-8 ERN NOAM MEAN TROF THAT IS MUCH FLATTER THAN THE
DEEP TROF THAT SHOULD BE OVER THE ERN CONUS DURING DAYS 3-5
SUN-TUE AND RAPIDLY WEAKEN THEREAFTER.
FEEDBACK AND OTHER SHORT RANGE DETAIL ISSUES PRECLUDE USE OF THE
00Z GFS FOR THE DOMINANT ERN NOAM SYSTEM BY DAY 3 SUN.
CONVERGENCE AMONG THE 00Z ECMWF AND GEFS MEAN SOLNS PROVIDES SOME
DEGREE OF CONFIDENCE IN SUCH AN EVOLUTION THOUGH A MODERATE AMOUNT
OF SPREAD STILL EXISTS AMONG REMAINING GUIDANCE. FOLLOWING THE
00Z ECMWF YIELDS FAIRLY MODEST CONTINUITY CHANGES WITH THE SFC
PATTERN DURING THE PERIOD. MODEL AND ENSEMBLE MEAN SOLNS
GENERALLY SHOW GOOD CONTINUITY AND AGREEMENT WITH THE CANADIAN
SYSTEM WHICH SHOULD PUSH A COLD FRONT INTO THE NRN TIER STATES BY
NEXT WED-THU.
ALONG THE WEST COAST THE 00Z GFS IS NOT AN OUTLIER RELATIVE TO THE
FULL ENVELOPE OF GEFS ENSEMBLE MEMBERS. HOWEVER THE 00Z GEFS MEAN
AND 12Z ECMWF/CANADIAN ENSEMBLE MEANS ALONG WITH OTHER OPERATIONAL
SOLNS SUGGEST THE GFS MAY BE TOO AGGRESSIVE WITH ITS NEGATIVELY
TILTED TROF THAT REACHES THE WEST COAST BY WED-THU.
TELECONNECTIONS RELATIVE TO A CORE OF NEGATIVE HGT ANOMALIES
APPEARING IN D+8 MEANS ON AVERAGE NEAR 50N 150W WOULD FAVOR A MEAN
RIDGE JUST INLAND FROM THE WEST COAST... FURTHER SUPPORTING
HOLDING HGT FALLS FARTHER WWD THAN THE GFS.
THE DAYS 3-5 SUN-TUE FCST FOLLOWS THE 00Z ECMWF BASED ON ITS
PREFERRED HANDLING OF THE SYSTEM AFFECTING THE ERN HALF OF NOAM.
DAYS 6-7 WED-THU TREND INCREASINGLY TOWARD THE 00Z ECMWF ENSEMBLE
MEAN TO DEPICT A LESS AMPLIFIED EVOLUTION OF SRN CANADA/NRN CONUS
FLOW COMPARED TO THE 00Z ECMWF AND FOLLOW THE NON-GFS CONSENSUS
WITH FLOW NEAR THE WEST COAST.
FINAL...
THE MAIN DIFFERENCE BETWEEN THE 12Z DETERMINISTIC GFS AND THE 00Z
RUN IS THAT IT BACKED OFF THE AGGRESSIVE HEIGHT FALLS ACROSS THE
INTERIOR NORTHWEST DAY 7...MORE IN LINE WITH THE OTHER 00Z
GUIDANCE...THE TELECONNECTIONS THEY IMPLIED...AND THE 12Z
DETERMINISTIC ECMWF. CONSEQUENTLY...MADE NO ADJUSTMENTS TO THE
FRONTS AND PRESSURES FOR THE FINAL ISSUANCE.
CISCO/RAUSCH
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