HPC Discussion
Posted by JAC on 6/15/2009, 7:37 am





PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
448 AM EDT MON JUN 15 2009

VALID 12Z FRI JUN 19 2009 - 12Z MON JUN 22 2009

OPERATIONAL MODELS AND ENSEMBLES CONTINUE TO SHOW SOME DEGREE OF
SPREAD AND RUN TO RUN VARIABILITY REGARDING THE DETAILS OF
EXPECTED ERN PAC/WEST COAST TROF AMPLIFICATION AND RESULTING
AMPLIFICATION OF A TROF OVER THE ERN CONUS.  THE GFS IS A FAST
OUTLIER COMPARED TO OTHER OPERATIONAL SOLNS WITH A PIECE OF PAC
ENERGY WHICH THE MODEL BRINGS TO THE WEST COAST BY EARLY DAY 6
SUN... SO OTHER GFS DETAILS OF THE EVOLVING WEST COAST TROF MAY BE
SUSPECT AS WELL.  AFTER DISPLAYING SOME DIFFICULTIES WITH THE
TRACK OF THE NERN PAC CLOSED LOW IN SOME EARLY RUNS... LATEST
ECMWF RUNS APPEAR TO HAVE STABILIZED SOMEWHAT WITH THE 00Z RUN
COMPARING FAIRLY WELL TO ENSEMBLE MEANS AND THE 00Z CANADIAN.
CORRESPONDING TO GFS DETAIL DIFFS OVER THE ERN PAC... THE GFS
BECOMES A LITTLE FLATTER THAN THE AVERAGE OF OPERATIONAL SOLNS OR
RECENT CONTINUITY AS THE TROF CROSSING THE NRN HALF OF THE CONUS
REACHES THE GRTLKS/OH VALLEY.  THEN BY DAY 7 MON THE GFS SHOWS AN
EMBEDDED CLOSED LOW FARTHER WWD/NWWD THAN OTHER MODEL SOLNS OR
ENSEMBLE MEANS.  TELECONNECTIONS RELATIVE TO THE ERN PAC/WEST
COAST TROF AND EVOLVING POSITIVE HGT ANOMALIES JUST E OF HUDSON
BAY WOULD FAVOR THE DOMINANT SOLN CLUSTER THAT IS FARTHER E THAN
THE GFS WITH THE CORE OF THE MEAN TROF.  AWAY FROM THESE
FEATURES... OVER THE PAST DAY THE GFS HAS ADJUSTED CONSIDERABLY
TOWARD THE STABLE ECMWF CONSENSUS WITH THE CLOSED LOW FORMING TO
THE W OF BAJA AND THEN EJECTING NEWD AHEAD OF THE AMPLIFYING ERN
PAC TROF.  MEANWHILE DIFFS ARE RELATIVELY MINOR WITH WEAK ENERGY
CROSSING THE NERN CONUS DAYS 3-4 THU-FRI.  SHORT RANGE GUIDANCE
AND TO SOME EXTENT 00Z GEFS ENSEMBLES DO NOT SUPPORT THE STRENGTH
AND NWD POSN OF THE GFS WAVE DEPICTED ALONG THE NC COAST AS OF
EARLY THU.

THE DAY 3 THU FCST FOLLOWS THE 00Z ECMWF DUE TO THE OUTLIER GFS
SOLN ALONG THE EAST COAST AND REASONABLE COMPARISON TO OTHER
GUIDANCE ELSEWHERE.  DAYS 4-5 FRI-SAT ADD SOME WEIGHTING OF THE
00Z GEFS AND 12Z/14 ECMWF ENSEMBLE MEANS AS DETAIL DIFFS EMERGE...
WHILE DAYS 6-7 SUN-MON START WITH A NEARLY EVEN BLEND OF 00Z
ECMWF/00Z GEFS MEAN/12Z ECMWF MEAN TO EMPHASIZE AGREEMENT WITH
LARGE SCALE FLOW AND TELECONNECTION SUPPORT TOWARD A FARTHER EWD
ERN NOAM TROF THAN FCST BY THE GFS LATE IN THE PERIOD.

RAUSCH


EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
149 PM EDT SUN JUN 14 2009

VALID 12Z WED JUN 17 2009 - 12Z SUN JUN 21 2009

THE OVERALL SPREAD AMONG OPERATIONAL MODELS AND ENSEMBLES HAS
DECREASED SLIGHTLY OVER THE PAST 24 HRS WITH RESPECT TO THE ERN
PAC TROF FORECAST TO AMPLIFY JUST OFF THE WEST COAST DURING THE
LATTER HALF OF THE MEDIUM RANGE PERIOD.  ON THE OTHER
HAND...SOLUTIONS STILL VARY DOWNSTREAM WITH SIGNIFICANT CONTINUITY
CHANGES FOR RESULTING ERN NOAM TROF AMPLIFICATION.  THIS INCLUDES
THE MOST RECENT 12 UTC GUIDANCE SO PREFER TO MAINTAIN HPC
CONTINUITY FOR NOW. 

THE 00Z ECMWF HAS BECOME MORE AMPLIFIED THAN PAST RUNS WITH THE
TROF WHICH TRACKS EWD FROM THE WEST THRU THE PERIOD...AND THE
NOGAPS/UKMET/GEFS ENSEMBLES CONCUR TO VARYING DEGREES.  GFS RUNS
HAVE BEEN SUGGESTING MORE AMPLIFICATION STARTING WITH ITS 06Z RUN
YESTERDAY...BUT THE 00 AND 12Z GFS RUNS ARE PARTICULARLY
STRONG/FAST OUTLIERS COMPARED TO GEFS AND ECMWF/CANADIAN ENSEMBLES
DURING WED-FRI.  THESE GFS RUNS THEN BECOMES SLOWER THAN CONSENSUS
WITH THE ERN TROF NEXT WEEKEND.  TELECONNECTIONS RELATIVE TO THE
EVOLVING CORE OF NEGATIVE HEIGHT ANOMALIES OVER THE NERN PAC SEEM
TO FAVOR SOME DEGREE OF ERN NOAM TROFFING...BUT WITH MORE MODERATE
NEG HEIGHT ANOMALIES AND SLIGHTLY FASTER PROGRESSION THAN THE 00Z
GFS LATE PERIOD. 

ELSEWHERE...THE 00Z GFS CONTINUES TO HAVE AN OUTLIER DEEP/WWD
SOLUTION FOR THE UPPER LOW FCST TO CUT OFF TO THE WEST OF BAJA AND
EVENTUALLY EJECT NEWD IN RESPONSE TO THE AMPLIFYING ERN PAC
FLOW... INDICATING SOME MID LEVEL HEIGHTS REACHING 3-5 STANDARD
DEVIATIONS BELOW NORMAL.  NERN PAC EVOLUTION IN THE 00Z GFS IS
ALSO QUESTIONABLE...WITH THE INITIAL NRN PAC CLOSED LOW DRIFTING
INTO NRN BC WHILE ANOTHER CLOSED LOW FORMS TO THE S...VERSUS THE
ECMWF AND GEFS/ECMWF ENSEMBLE MEANS THAT MAINTAIN ONE NERN PAC
CLOSED LOW.  MEANWHILE...SHORT RANGE FEEDBACK IN THE 00Z GFS
YIELDS A STRONGER/FASTER WRN ATLC SURFACE LOW THAN OFFERED BY
OTHER MODEL/ENSEMBLE SOLUTIONS AS EARLY AS WED.

IN SUMMARY...DUE TO THE MULTIPLE OUTLIER ASPECTS OF THE 00Z GFS
FROM THE START OF THE MEDIUM RANGE FCST...DAYS 3-4 WED-THU START
WITH A SOLUTION CLOSEST TO THE 00Z ECMWF.  THE 06Z GFS HAS ALSO
TRENDED TOWARD THIS SOLUTION.  THERE ARE CONTINUITY ISSUES...BUT
THE UPDATED HPC PRELIM PROGS CONTINUED TO EASE INCREASINGLY INTO A
MORE AMPLIFIED ERN NOAM MID-UPPER LEVEL TROF SCENARIO AS PER
SLOWLY BUILDING CONSENSUS...BUILDING UPSTREAM RIDGING...AND AT THE
MODEST TROF SUPPORTED BY TELECONNECTIONS.  THIS LEADS TO A DAYS
5-7 FRI-SUN FORECAST THAT IS WEIGHTED 60% 00Z ECMWF/ECMWF ENSEMBLE
MEAN WITH THE REST LEANING ON THE 00Z GEFS MEAN WHOSE SOLUTION IS
MORE AMPLIFIED THAN THE EC/EC ENS MEAN...BUT NOT TO THE EXTENT OF
THE 00Z GFS. WE SEE NO STRONG COMPELLING REASON TO CHANGE HPC
CONTINUITY FOR THE FINAL PROGS BASED ON LATEST AND STILL VARIED 12
UTC MODEL AND ENSEMBLE GUIDANCE. 

RAUSCH/SCHICHTEL
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Possible Severe Weather this Weekend for Great-Lakes & Ontario - JAC, 6/15/2009, 7:29 am
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