482
FXUS02 KWBC 271647
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1247 PM EDT TUE MAY 27 2008
VALID 12Z FRI MAY 30 2008 - 12Z TUE JUN 03 2008
PRELIMINARY...
USED THE 00Z ECMWF FOR DAYS 3 THROUGH 5 FOR THE PRELIMINARY FRONTS
AND PRESSURES...WITH A GRADUAL BLEND TOWARD THE 00Z ECMWF ENSEMBLE
MEAN THEREAFTER TO REFLECT THE UNCERTAINTY IN DETAILS INHERENT AT
THAT TIME RANGE. THE 00Z GFS IS A FAST OUTLIER AGAINST THE 00Z
ECMWF...EC MEAN...AND GEM ENSEMBLE MEAN WITH THE SHORTWAVE
CROSSING THE UPPER MIDWEST ON DAY 3. THE GFS IS THEN FAST AGAINST
THE SAME SET OF GUIDANCE WITH THE TROUGH EDGING INTO THE WEST
COAST DAY 4. BY DAY 6...THE GFS GAINS THE SUPPORT OF THE GEM MEAN
WITH THE TROUGH PROGRESSING INTO THE INTERIOR WEST...BUT THEN
OUTRUNS THE GEM MEAN BY DAY 7. EACH WEEK INTO SUMMER WILL MAKE IT
MORE AND MORE DIFFICULT FOR COLD POOLS TO PROGRESS OVER THE
HEATED...ELEVATED TERRAIN OF THE WEST...SO PREFER THE MORE
CLIMATOLOGICAL PROJECTIONS FROM THE DETERMINISTIC ECWMF AND ITS
ENSEMBLE MEAN KEEPING THE HEART OF THE LONG WAVE TROUGH OFF THE
PACIFIC COAST. A WEAK PUSH OF MARITIME POLAR AIR INTO THE GREAT
BASIN SEEMS SUPPORTED DAYS 6 AND 7...BUT SHOULD MODERATE RAPIDLY
SHORTLY BEYOND THE FORECAST PERIOD.
FINAL...
THE 12Z GFS HAS BACKED OFF THE HEIGHT FALLS OVER THE NORTHERN
INTERMOUNTAIN REGION AND NORTHERN ROCKIES DEPICTED ITS 00Z RUN DAY
5...INDICATING A SLOWER PROGRESSION OF THE OFFSHORE TROUGH INTO
THE WEST THEREAFTER...WITH LESS AMPLITUDE. THIS TREND FITS
CLIMATOLOGY BETTER...AND WOULD ASSUME THAT WITH FUTURE
RUNS...CHANCES ARE GOOD THAT THE MODEL WILL BACK OFF FURTHER WITH
THIS SYSTEM...TOWARD THE SOLUTIONS SHOWN BY THE 00Z ECMWF AND ITS
ENSEMBLE MEAN. THE TWO MAIN PRECIPITATION PRODUCERS THIS PERIOD
LOOK TO BE THE WAVE CROSSING THE MIDWEST AND GREAT LAKES DAY
3...AND THE SYSTEM ORGANIZING OVER THE NORTHERN PLAINS DAY 6.
..FOR THE ALASKA MEDIUM RANGE FORECAST PRODUCTS
PLEASE REFER TO
THE HPC HOMEPAGE...
CISCO
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