HPC Discussion
Posted by JAC on 10/27/2009, 2:51 pm
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
940 AM EDT TUE OCT 27 2009

VALID 12Z SAT OCT 31 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 FCST FOR THIS PART OF THE
FCST.

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.

...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
35
In this thread:
Possible Severe System for MS-Valley/Midwest around the Weekend - JAC, 10/26/2009, 3:53 pm
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