131
FXUS02 KWBC 271816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
216 PM EDT TUE OCT 27 2009
VALID 12Z FRI OCT 30 2009 - 12Z TUE NOV 03 2009
MOST MEDIUM RANGE GUIDANCE CONTINUES TO INDICATE AN EVOLUTION FROM
A DEEP/AMPLIFIED CNTRL NOAM MEAN TROF TOWARD LOWER AMPLITUDE MEAN
FLOW BY SUN-TUE... WITH A HINT OF A FLAT RIDGE OVER THE WEST AND A
MODEST MEAN TROF OVER THE ERN HALF OF THE CONUS. THIS LATE PERIOD
CONFIGURATION IS REASONABLY CONSISTENT WITH TELECONNECTIONS
RELATIVE TO N-CNTRL ATLC AND NRN PAC POSITIVE HGT ANOMALY CENTERS
INDICATED IN LATEST D+8 MULTI-DAY MEAN FCSTS.
SOME TRACK/TIMING DIFFS PERSIST WITH A VIGOROUS SYSTEM FCST TO BE
OVER/NEAR MN ALONG WITH A RAPIDLY APPROACHING SECOND SYSTEM OVER
AND/OR WRN CANADA AS OF EARLY DAY 3 FRI... WHICH SHOULD MERGE TO
YIELD A VERY DEEP SFC LOW OVER E-CNTRL CANADA. THE 00Z/06Z GFS
AND 00Z ECMWF/EC ENSEMBLE MEAN NOW PROVIDE A GOOD MAJORITY CLUSTER
WITH THE MN SYSTEM VERSUS THE FARTHER SWD 00Z CMC/GEFS MEAN.
MEANWHILE WITH THE APCHG UPSTREAM SYSTEM THE 00Z/06Z GFS ARE ON
THE FAST EDGE OF GUIDANCE. AS A RESULT ECMWF/EC MEAN GUIDANCE
APPEARS TO PROVIDE THE BEST OVERALL SOLN FOR THIS PART OF THE
FCST.
THE NEXT SYSTEM OF NOTE THIS PERIOD WILL BE AN AREA OF LOW
PRESSURE THAT SHOULD APPROACH THE BC COAST BY EARLY DAY 4 SAT AND
THEN TRACK ACROSS SRN CANADA AND NRN CONUS DURING THE REMAINDER OF
THE PERIOD. AS OF EARLY SAT THE 06Z GFS IS ON THE SRN EDGE OF THE
MODEL/ENSEMBLE MEAN SPREAD... AND THEN BECOMES A STRONG AND
EVENTUALLY FAST OUTLIER FARTHER EWD. THE 00Z GFS MAY BE A LITTLE
SLOW BY DAY 7 TUE BUT OVERALL COMPARES BETTER TO THE PREFERRED 00Z
ECMWF/GEFS MEAN/ECMWF MEAN CLUSTER AT THAT TIME.
LATEST GFS RUNS INDICATE POTENTIAL FOR LOW PRESSURE TO REACH THE
PAC NW OR SWRN CANADA BY NEXT MON-TUE. THE 00Z GFS IS NOT AN
OUTLIER BUT IS STILL FAIRLY FAR SWD WITHIN THE OVERALL ENSEMBLE
ENVELOPE. THE FARTHER NWWD 06Z GFS TRACK COMPARES SOMEWHAT BETTER
TO THE AVG OF ENSEMBLES BUT THE DEPTH IS IN THE STRONGER THIRD OF
GEFS MEMBERS. TELECONNECTION-FAVORED MEAN FLOW DOES FAVOR A
MODEST ERN PAC MEAN TROF... WHICH IS FAIRLY WELL DEPICTED IN THE
00Z GEFS/ECMWF ENSEMBLE MEANS... SO WILL LEAN TOWARD THEIR IDEA OF
A WEAK NERN PAC SFC LOW AS OF EARLY DAY 7 TUE AS A REASONABLE
STARTING POINT.
12Z UPDATE... BY DAY 3 FRI THE NEW GFS IS MORE PROGRESSIVE THAN
ONGOING MODEL/ENSEMBLE CONSENSUS FROM THE NERN PAC ACROSS SRN
CANADA/NRN CONUS. THIS LIKELY CONTRIBUTES TO THE GFS LEAVING
RESIDUAL SRN STREAM ENERGY FARTHER BEHIND THAN OTHER SOLNS BY DAY
4 SAT... AND HENCE THE WAVE REACHING THE EAST COAST BY EARLY DAY 5
SUN IS QUESTIONABLE. THE 12Z UKMET MAY ALSO BE TOO PROGRESSIVE
DURING THE LATE SHORT RANGE/EARLY MEDIUM RANGE BUT COMES INTO
SOMEWHAT BETTER AGREEMENT BY SAT-SUN. MID-LATE PERIOD... THE 12Z
GFS/UKMET/CMC ARE ALL FASTER THAN ECMWF RUNS AND GEFS/EC ENSEMBLE
MEANS WITH THE SYSTEM REACHING THE NRN PLAINS BY EARLY DAY 5 SUN.
THEN BY THE END OF THE FCST THE GFS IS MORE AMPLIFIED THAN MOST
GUIDANCE WITH OVERALL ERN PAC/NOAM FLOW. HOWEVER THE 12Z CMC BY
DAY 6 APPEARS TO BE HEADED FOR A FAIRLY AMPLIFIED SOLN AS WELL AND
THE TROF/RIDGE/TROF ALIGNMENT COMPARES FAVORABLY TO THE EXPECTED
MEAN PATTERN. AT THIS TIME WILL AWAIT CONFIRMATION OF THESE
MID-LATE PERIOD 12Z GUIDANCE TRAITS AS THEY CANNOT BE DISCOUNTED
BUT CONFIDENCE IS NOT HIGH ENOUGH TO MAKE A SIGNIFICANT ADJUSTMENT
TOWARD THEM YET.
THE UPDATED PRELIM FCST USED A BLEND OF 00Z ECMWF.. 00Z ECMWF
ENSEMBLE MEAN.. AND 12Z/26 ECMWF FOR DAYS 3-5 FRI-SUN TO EMPHASIZE
THE BEST OPERATIONAL CLUSTER OF GUIDANCE OVER CNTRL-ERN NOAM AND
NERN PAC WHILE PROVIDING MODEST SMOOTHING OF YET TO BE RESOLVED
DETAILS. THE FAIRLY STRONG ERN PAC RIDGE WHICH THE 12Z/26 ECMWF
SHOWS OVER THE ERN PAC BY NEXT TUE DOES NOT COMPARE WELL TO
TELECONNECTIONS OR MOST OTHER GUIDANCE. AS A RESULT THE 12/26
ECMWF COMPONENT OF THE BLEND WAS REPLACED WITH THE 00Z GEFS MEAN
FOR DAYS 6-7 MON-TUE. SHORT RANGE PREFERENCES DO NOT FAVOR THE
FARTHER WWD 00Z ECMWF FOR THE SYSTEM TRACKING AWAY FROM MN ON
FRI... SO THE FINAL FCST ADJUSTS SOMEWHAT TOWARD OTHER GUIDANCE
EARLY FRI. NO OTHER CHANGES WERE MADE FOR THE FINAL ISSUANCE.
REGIONAL HIGHLIGHTS...
..WEST
EXPECT PCPN TO BE CONFINED TO NRN AREAS THRU THE PERIOD... FROM
THE NRN HALF OF THE WEST COAST INTO THE NRN ROCKIES. PCPN SHOULD
BE PERSISTENT IN THE NRN PART OF THIS REGION WHILE THE SRN EXTENT
OF THE PCPN SHIELD WILL VARY SOMEWHAT FROM FRI THRU NEXT TUE.
HIER ELEVS OF THE ROCKIES SHOULD SEE SOME SNOW WHILE TEMPS SHOULD
BE WARM ENOUGH FOR MOSTLY RAIN ELSEWHERE. HIGHEST TOTALS WILL
LIKELY OCCUR ALONG FAVORED WWD-FACING TERRAIN. FRI SHOULD BE
CHILLY OVER THE ROCKIES. OTHERWISE ANTICIPATE NEAR NORMAL DAYTIME
TEMPS UNDER CLOUDS/PCPN IN THE NORTH AND ABOVE NORMAL READINGS
WITH FAIR AND DRY WEATHER CENTRAL/SOUTH.
..CENTRAL/EAST
THE COLD FRONT TRAILING FROM A VIGOROUS NRN TIER CONUS/SRN CANADA
STORM WILL LIKELY BE ACCOMPANIED BY A BAND OF LOCALLY HVY RNFL
FROM THE LOWER MS VALLEY INTO THE E-CNTRL GRTLKS FRI INTO SAT.
CONSULT LATEST SPC OUTLOOKS FOR FURTHER INFO REGARDING SEVERE
WEATHER THREAT. RNFL WITH THIS FRONT SHOULD BE MUCH LIGHTER
FARTHER EWD AS DYNAMICS ALOFT LIFT INTO CANADA. DURING FRI-SAT
EXPECT WELL ABOVE NORMAL TEMPS OVER THE EAST AHEAD OF THE FRONT...
WITH MODERATELY BELOW NORMAL READINGS TO THE WEST. BY LATE
WEEKEND/EARLY NEXT WEEK EXPECT NEAR TO ABOVE NORMAL DAYTIME
READINGS AT MOST LOCATIONS. RESIDUAL MSTR FROM THE UPR MS VLY TO
NEW ENGLAND MAY GENERATE SOME LGT PCPN THRU THE WEEKEND WHILE A
WEAK UPSTREAM SYSTEM MAY BE ACCOMPANIED BY LGT PCPN FROM THE NRN
PLAINS EWD/SEWD.
RAUSCH
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