599
FXUS02 KWBC 101807
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
206 PM EDT TUE JUN 10 2008
VALID 12Z FRI JUN 13 2008 - 12Z TUE JUN 17 2008
MULTI-DAY MEANS CONTINUE TO BE FAIRLY CONSISTENT IN DEPICTING AN
EVOLUTION WHICH BY D+8 LEADS TO AN EAST COAST MEAN TROF THAT IS
FAVORED BY A STRONG CORE OF POSITIVE HGT ANOMALIES NEAR THE DAVIS
STRAIT. THERE IS SOMEWHAT LESS AGREEMENT REGARDING THE STRENGTH
OF POSITIVE ANOMALIES OVER THE NRN PACIFIC NEAR THE ALEUTIANS...
WHICH LEADS TO DIFFERENCES IN TIMING AND AMPLITUDE OF NERN PAC
TROFFING EXPECTED TO APPROACH THE PAC NW COAST.
REGARDING THE PAC EVOLUTION... SOME RECENT RUNS OF THE ECMWF AND
EC ENSEMBLES HAVE BEEN WEAKER AND MORE ELONGATED THAN OTHER
GUIDANCE WITH NRN PAC/ALEUTIANS POSITIVE ANOMALIES AND THUS
FLATTER WITH ERN PAC FLOW THAT HEADS INTO THE NWRN CONUS/WRN
CANADA. ON THE OTHER HAND GFS AND GEFS ENSEMBLES HAVE BEEN
FARTHEST SEWD/MOST AMPLIFIED. THE MEAN OF WIDELY DISPERSED
CANADIAN ENSEMBLE MEMBERS IS GENERALLY BETWEEN THE ECMWF/GEFS
ENSEMBLE MEANS. WHILE GEFS MEANS HAVE TRENDED LITTLE... OVER THE
PAST DAY OPERATIONAL GFS RUNS HAVE BEEN TRENDING GRADUALLY SLOWER
TO BRING HGT FALLS INTO THE NORTHWEST. IN LIGHT OF THE ARRAY OF
LATEST GUIDANCE AND TRENDS OVER THE PAST DAY... THE 00Z
ECMWF/CANADIAN OFFER A REASONABLE INTERMEDIATE SOLN THAT AGREES
BETTER WITH CONTINUITY OF MOST D+8 MEANS OVER THE NRN PAC AND
OFFERS ACCEPTABLE AGREEMENT WITH TELECONNECTION FAVORED SWLY FLOW
OVER THE NWRN STATES BY LATE IN THE PERIOD.
FARTHER EWD THE 00Z/06Z GFS RUNS ARE GENERALLY ON THE FAST AND/OR
AMPLIFIED SIDE OF MOST GUIDANCE WITH THE SHRTWV TROF CROSSING THE
GRTLKS INTO THE EAST BY SAT-SUN. THE ECMWF HAS TRENDED SOMEWHAT
FASTER OVER ITS PAST 12-24 HRS OF RUNS THOUGH. PERHAPS WITH HELP
FROM SOME UPSTREAM ENERGY... GEFS AND CANADIAN ENSEMBLE MEANS ARE
NOTICEABLY MORE AGGRESSIVE THAN OTHER GUIDANCE WITH THE OVERALL
MEAN TROF THAT DIGS INTO THE EAST BY SUN-TUE. THE GEFS/CMC
ENSEMBLE MEAN SOLNS CANNOT YET BE FULLY DISCOUNTED GIVEN THE
TELECONNECTION SUPPORTED EAST COAST MEAN TROF BY D+8. HOWEVER AT
THIS TIME THERE IS ENOUGH UNCERTAINTY IN UPSTREAM FLOW TO WARRANT
A MORE MODERATE OR SLIGHTLY DELAYED AMPLIFICATION.
THE 00Z ECMWF PROVIDES THE BEST FOUNDATION FOR THE DAYS 3-7
FRI-TUE FCST GIVEN ITS INTERMEDIATE STANCE ON MOST SIGNIFICANT
FEATURES. THE ECMWF MAY BE OVERDONE WITH SFC DEVELOPMENT FROM THE
GRTLKS INTO QUEBEC MON-TUE... FAVORING A 30 PERCENT BLEND WITH THE
00Z CANADIAN TO MAINTAIN A LITTLE MORE SFC DETAIL THAN THE 00Z
ECMWF MEAN WHILE SUPPORTING A NERN PAC TROF ALOFT THAT IS NO LESS
AMPLIFIED THAN THE 00Z ECMWF.
12Z UPDATE... THE OVERALL ARRAY OF LATEST GUIDANCE GENERALLY
SUPPORTS THE PRELIM REASONING. THE 12Z GFS BECOMES FASTER THAN
06Z CONTINUITY OR OTHER 12Z MODELS WITH SIGNIFICANT FEATURES FROM
THE NERN PAC INTO THE ATLC. THE 12Z GEFS MEAN HAS MADE A
NOTICEABLY FLATTER ADJUSTMENT WITH NERN PAC FLOW TOWARD THE 00Z
ECMWF IDEA BUT IS STILL QUITE AGGRESSIVE WITH ITS AMPLIFYING ERN
TROF. RELATIVE SUPPORT FROM THE 12Z UKMET/CMC/GEFS MEAN OVER THE
NERN PAC... AND THE UKMET/CMC OVER THE ATLC... FAVOR KEEPING A
SOLN CLOSEST TO THE 00Z ECMWF. THEREFORE THE FINAL FCST REFLECTS
NO CHANGE FROM THE PRELIM ISSUANCE.
REGIONAL HIGHLIGHTS...
..WEST
A RIDGE ALOFT OVER NRN MEXICO AND SWRN CONUS WILL SUPPORT MOSTLY
FAIR WEATHER WITH ABOVE NORMAL TEMPS OVER MUCH OF THE
GRTBASIN/SOUTHWEST/CALIFORNIA REGION. DAYTIME TEMPS OVER THE
ROCKIES WILL MODERATE AFTER BEING AT BELOW NORMAL LEVELS FRI...
THOUGH A SYSTEM BRUSHING THE NRN TIER OVER THE WEEKEND WILL KEEP
NRN LOCATIONS NEAR TO SLIGHTLY BELOW NORMAL. SOME MODEST COOLING
IS ALSO POSSIBLE OVER THE EXTREME NORTHWEST AS A NERN PACIFIC TROF
ALOFT APPROACHES.
..CENTRAL/EAST
COLD FRONT EXTENDING FROM THE GRTLKS SWWD INTO THE PLAINS AS OF
EARLY FRI WILL PROMOTE SOME LOCALLY HVY RNFL ALONG ITS PATH AS IT
PROGRESSES EWD/SEWD OVER THE FOLLOWING 2-3 DAYS. CURRENT SPC
OUTLOOK ISSUED TUE INDICATES SOME POTENTIAL FOR SEVERE ACTIVITY
OVER PORTIONS OF THE SWRN-CNTRL GRTLKS IN THE FRI TO EARLY SAT
PERIOD. CONSULT SPC OUTLOOKS/DISCUSSIONS FOR FURTHER INFO
REGARDING THE SEVERE WEATHER THREAT. ANOTHER FRONT SHOULD PASS
THRU THE ERN HALF OF THE CONUS SUN-TUE AND BE ACCOMPANIED BY RAIN
AND TSTMS OF VARYING INTENSITY. THIS SUCCESSION OF FRONTS SHOULD
KEEP TEMPS VARIABLE OVER THE FCST PERIOD... BUT WITH SOMEWHAT MORE
CONSISTENTLY BELOW NORMAL READINGS OVER THE NRN PLAINS AND ON
AVERAGE A GENERAL COOLING TREND FROM FRI-TUE OVER THE EAST.
RAUSCH/CISCO
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