462
FXUS02 KWBC 091854
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
253 PM EDT MON JUN 09 2008
VALID 12Z THU JUN 12 2008 - 12Z MON JUN 16 2008
OVER THE COURSE OF THE MEDIUM RANGE PERIOD MULTI-DAY MEANS SHOW
BETTER THAN AVERAGE AGREEMENT WITH LARGE SCALE EVOLUTION. EXPECT
A STEADY EROSION OF AN AMPLIFIED W-CNTRL CONUS TROF WHILE POSITIVE
HGT ANOMALY CENTERS STRENGTHEN OVER OR NEAR THE ERN ALEUTIANS AND
THE DAVIS STRAIT. TELECONNECTIONS RELATIVE TO THE ALEUTIANS
CENTER GENERALLY FAVOR A NERN PAC TROF WITH SWLY FLOW ALONG AND
INLAND FROM THE WEST COAST... WHILE THOSE RELATIVE TO THE DAVIS
STRAIT CENTER FAVOR A MODEST EAST COAST TROF WITHIN A BAND OF
NEGATIVE HGT ANOMALIES CENTERED ALONG 40N LATITUDE EXTENDING FROM
THE ERN CONUS EWD THRU MUCH OF THE ATLANTIC. AN EAST COAST TROF
ALBEIT WITH SOMEWHAT HIGHER HGTS IS ALSO FAVORED BY THE EXPECTED
PACIFIC PATTERN.
INSPECTION OF LATEST MODEL AND ENSEMBLE GUIDANCE SUGGESTS THREE
PRIMARY FCST ISSUES DURING THE PERIOD. FROM EAST TO WEST THESE
ARE THE AMPLITUDE/POSN OF A FAIRLY DEEP WRN ATLANTIC TROF AND
EMBEDDED CLOSED LOW... EVOLUTION/TIMING OF THE TROF EJECTING FROM
THE W-CNTRL CONUS... AND FLOW ACROSS THE NERN PACIFIC/NWRN NORTH
AMERICA. OVER THE PAST WEEK SOME INDIVIDUAL RUNS OF THE GFS AND
ECMWF HAVE EACH HAD SOME SERIOUS FLAWS SO CONFIDENCE IN ONE
PARTICULAR SOLN TODAY IS MODERATE AT BEST. WITH THE WRN ATLC
EVOLUTION... THRU 00Z/06Z RUNS THERE IS NO CLEAR CONSENSUS BETWEEN
A MORE AMPLIFIED SOLN SUCH AS THE 00Z ECMWF VERSUS LESS AMPLIFIED
GFS/GEFS MEAN RUNS. OVERALL CONSENSUS OF REMAINING GUIDANCE SEEMS
TO LEAN SLIGHTLY MORE IN THE ECMWF DIRECTION. THERE IS ALSO
MODERATE SCATTER WITH THE EJECTING W-CNTRL CONUS TROF THAT BRINGS
HGT FALLS INTO THE GRTLKS/OH VALLEY/NORTHWEST BY MID-LATE
PERIOD... INCLUDING UNCERTAINTY REGARDING THE PROPORTION OF ENERGY
THAT MAY UNDERCUT THE MEAN RIDGE OVER ERN CANADA/EXTREME NRN ATLC.
AT LEAST INTO DAY 5 SAT THE 00Z/06Z GFS RUNS AND ENSEMBLE MEANS
MAY BE A TAD FAST WITH LEADING HGT FALLS... ESPECIALLY CONSIDERING
THE STRONG ERN CONUS MEAN RIDGE IN PLACE. HOWEVER BY LATE IN THE
PERIOD THE TELECONNECTION FAVORED MEAN PATTERN HINTS AT SOMEWHAT
MORE AMPLIFIED EAST COAST FLOW THAN FCST BY THE 00Z ECMWF. AS FOR
FLOW OVER THE NERN PAC AND VICINITY... THE BEST POINT OF AGREEMENT
IS THAT 00Z/06Z GFS AND GEFS MEAN RUNS ARE LIKELY OVERDONE IN
THEIR EXTENT OF HGT FALLS OVER THE NORTHWEST BY DAYS 6-7 SUN-MON.
TELECONNECTIONS RELATIVE TO THE UPSTREAM RIDGE INDICATE POTENTIAL
FOR THE AXIS OF THE MEAN TROF OVER THE NERN PAC TO REACH CLOSER TO
THE PAC NW COAST BY DAY 7 THAN FCST BY THE 00Z ECMWF THOUGH.
BASED ON THE ABOVE CONSIDERATIONS WHICH GENERALLY FAVOR LEANING
MORE TOWARD ECMWF IDEAS VERSUS THE GFS BUT WITH SOME ADJUSTMENTS
BY MID-LATE PERIOD... THE UPDATED PRELIM FCST FOR DAYS 3-4 THU-FRI
FCST MAINTAINED THE 00Z ECMWF SOLN WHILE DAYS 5-7 SAT-MON
INCORPORATED 30 PERCENT OF THE 00Z GEFS MEAN.
12Z UPDATE... OVERALL THE 12Z GUIDANCE CONTINUES TO FAVOR AN
INTERMEDIATE SOLN BETWEEN THE 00Z ECMWF AND 00Z/06Z GFS RUNS WITH
FLOW OVER THE NERN PAC AND VICINITY. DETAILS REMAIN IN QUESTION
BUT THERE IS REASONABLE CONSENSUS UPON SOMEWHAT MORE PROGRESSIVE
FLOW COMPARED TO THE 00Z ECMWF FROM CNTRL NOAM INTO THE ATLC.
THEREFORE OVER THAT AREA THE FINAL FCST ADJUSTS TOWARD A MORE EVEN
BLEND OF THE 00Z ECMWF AND NEW 12Z GUIDANCE PRIMARILY FOR DAYS
3-6.
REGIONAL HIGHLIGHTS...
..CENTRAL/EAST
COLD FRONT AND SUPPORTING DYNAMICS ALOFT MAY SUPPORT SOME LOCALLY
HVY CONVECTION FROM THE UPR GRTLKS SWWD INTO THE CNTRL PLAINS IN
THE THU-FRI TIME FRAME. CURRENT SPC OUTLOOK ISSUED ON MON
INDICATES SOME OF THIS ACTIVITY MAY ALSO BE SEVERE FROM NRN MO
INTO THE U.P. OF MI. PLEASE CONSULT FUTURE SPC OUTLOOKS FOR THE
LATEST INFO REGARDING SEVERE THREAT. AS THE COLD FRONT HEADS
EWD/SEWD FROM FRI ONWARD... STILL EXPECT IT TO BE ACCOMPANIED BY
SOME SHWRS/TSTMS BUT CONFIDENCE IN PINPOINTING STRENGTH AND RNFL
AMTS IS LOW. THE NRN PLAINS WILL SEE VERY CHILLY DAYTIME TEMPS
THU WITH RAPID MODERATION THEREAFTER... WHILE WARM TO HOT WEATHER
INITIALLY AHEAD OF THE FRONT WILL SIMILARLY MODERATE AFTER
THU-FRI. AS A RESULT TEMPS BY SAT-MON SHOULD BE WITHIN A FEW
DEGREES OF NORMAL AT MOST LOCATIONS.
..WEST
WELL BELOW NORMAL DAYTIME TEMPS OVER THE NORTHERN TWO THIRDS OF
THE ROCKIES/INTERMOUNTAIN WEST... WITH SOME RAIN AND HIGH
ELEVATION SNOW OVER THE NRN ROCKIES... ON THU WILL QUICKLY GIVE
WAY TO DRY WEATHER WITH NEAR TO ABOVE NORMAL TEMPS FOR THE
REMAINDER OF THE PERIOD. THERE IS SOME UNCERTAINTY OVER THE
POTENTIAL FOR A COOLING TREND OVER THE NORTHWEST DURING THE
WEEKEND/EARLY NEXT WEEK... BUT THE MOST LIKELY SCENARIO AT THIS
TIME IS TOWARD ONLY A MODEST CHANGE. THE REMAINDER OF THE WEST
SHOULD SEE FAIR WEATHER WITH ABOVE NORMAL DAYTIME TEMPS.
RAUSCH
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