417
FXUS02 KWBC 241803
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
146 PM EDT SAT MAY 24 2008
VALID 12Z TUE MAY 27 2008 - 12Z SAT MAY 31 2008
THE MULTI-DAY MEANS BY D+8 HAVE COME INTO REASONABLE AGREEMENT
WITH A CORE OF NEGATIVE ANOMALIES TO THE S OF THE CNTRL ALEUTIANS
YIELDING TELECONNECTION-SUPPORTED SPLIT FLOW ALONG THE WEST COAST.
ASIDE FROM LOW CONFIDENCE SMALLER SCALE DETAILS THE OPERATIONAL
MODELS AND ENSEMBLES ARE SIMILAR IN DEPICTING A NEWD EJECTION OF
ERN PAC CLOSED LOW ENERGY INTO THE NRN PLAINS DURING TUE-FRI AS
EITHER FURTHER PACIFIC ENERGY APPROACHES OR SOME OF THE INITIAL
ERN PAC ENERGY EVOLVES IN PLACE OVER THE WEST COAST TO MAINTAIN
THE MEAN TROF. MEANWHILE MODERATE ERN CANADA TROFFING SHOULD
EXTEND INTO THE NERN CONUS IN RESPONSE TO THE MEAN RIDGE OVER WRN
CANADA/ALASKA... WITH WEAKER IMPULSES SUPPORTING A SHRTWV TROF
FCST TO REACH THE EAST COAST BY FRI.
ONE OF THE MORE NOTICEABLE DIFFERENCES THIS CYCLE IS THAT COMPARED
TO OTHER GUIDANCE BY MID TO LATE PERIOD... THE 00Z GFS/GEFS MEAN
BECOME MORE AMPLIFIED WITH ALASKA/CANADA FLOW. THIS RESULTS IN
THOSE SOLNS BRINGING A STRONGER NRN STREAM SHRTWV INTO THE GRTLKS
BY DAY 7 SAT. FAST TIMING OF THE GFS COULD STILL PROVIDE THE
RELATIVELY FLAT MEAN PATTERN WHICH TELECONNECTIONS SUGGEST ALONG
THE ERN HALF OF THE US-CANADIAN BORDER WHEN VIEWED FROM A
MULTI-DAY MEAN BUT FOR NOW PREFER TO GO WITH THE FLATTER CONSENSUS
CLOSER TO THE ECMWF WHICH FITS BETTER WITH THE GRADUALLY FLATTER
TREND OF THE LARGE SCALE MEAN PATTERN.
MEANWHILE THERE IS STILL SOME SPREAD WITH THE EVENTUAL SWD EXTENT
OF THE COLD FRONT FCST TO EXTEND FROM NEW ENGLAND INTO THE CNTRL
PLAINS AS OF EARLY TUE... DEPENDING ON THE EXACT AMPLITUDE OF THE
MID LVL TROF REACHING THE EAST COAST BY LATE WEEK. BEST
CLUSTERING OF OPERATIONAL MODELS... WITH SUPPORT FROM THE 12Z/23
ECMWF/CANADIAN ENSEMBLE MEANS... CONTINUES TO FAVOR SLIGHTLY LESS
TROF STRENGTH THAN THE 00Z GFS AND GEFS MEAN. THUS PREFER TO LEAN
MORE TOWARD THE 00Z ECMWF WHICH IS SLIGHTLY SLOWER THAN THE GFS
WITH PORTIONS OF THE SFC FRONT AND OFFERS SOMEWHAT BETTER
CONTINUITY FROM PREVIOUS HPC FCST.
THE EARLY PRELIM FCST USES THE 00Z ECMWF FOR DAYS 3-4 TUE-WED
BASED ON THE ABOVE CONSIDERATIONS FOR THE CNTRL-ERN CONUS FRONT AS
WELL AS SHORT RANGE EVOLUTION THAT APPEARS TO BE BETTER
REPRESENTED BY THE ECMWF. THE FCST THEN INCORPORATES HALF
WEIGHTING OF THE 12Z/23 ECMWF ENSEMBLE MEAN FOR DAYS 5-7 THU-SAT
TO LEAN AWAY FROM THE QUESTIONABLY AMPLIFIED GFS/GEFS MEAN WITH
THE CANADA SHRTWV REACHING THE GRTLKS AROUND SAT AND TO ACCOUNT
FOR ADDED DETAIL UNCERTAINTY AT THE LONGER TIME FRAME.
LATEST 00Z ECMWF ENS MEAN VERY SIMILAR TO THE 12Z/23 VERSION WHILE
THE 06Z GFS INDICATES A MODERATE TREND TOWARDS THE LESSER
AMPLIFIED ECMWF DAY 7 WITH THE GREAT LAKES SHORTWAVE.
TROPICS
GFS SERIES HAVE BEEN INDICATING WRN CARRIBEAN TROPICAL DEVELOPMENT
FOR OVER A WEEK AT LONGER RANGES INDICATING INCREASING FAVORABLE
CONDS FOR TROPICAL DEVELOPMENT. LATEST OVERNIGHT RUNS AND TODAYS
12Z RUN ALONG WITH A LARGE NUMBER OF ENSEMBLE MEMBERS WITH WELL
ABOVE AVERAGE LOCATIONAL CLUSTERING CONT THIS TREND. 00Z ECMWF
ALSO DEVELOPS LOW PRESSURE IN THIS AREA BUT NOT TO THE DEVELOPED
EXTENT OF THE GFS. CMC ALSO LIKES THIS GENERAL REGION BUT PLACES
ITS EMPHASIS ON THE PAC SIDE. AFTN FINAL PROGS WILL DEPICT A GFS
ENS MEAN AREA OF LOW PRESSURE OFF THE NICARAGUA COAST DAYS 5-7
THU-SAT.
RAUSCH/ROSENSTEIN
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