HPC has some confidence with this one
Posted by JAC on 1/20/2011, 3:13 pm
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
202 PM EST THU JAN 20 2011

VALID 12Z SUN JAN 23 2011 - 12Z THU JAN 27 2011

MEDIUM RANGE GUIDANCE CONTINUES TO DISPLAY MEANINGFUL SPREAD WITH
IMPORTANT SHRTWV DETAILS WITHIN AN AMPLIFIED ERN PAC/WEST COAST
MEAN RIDGE AND ERN NOAM MEAN TROF CONFIGURATION.  ONE OF THE MOST
SIGNIFICANT UNCERTAINTIES YET TO BE RESOLVED INVOLVES THE EXACT
SHAPE OF THE RIDGE AS OF DAY 4 MON... AND IMPACT ON DOWNSTREAM
FLOW.  OPERATIONAL ECMWF RUNS AND ECMWF ENSEMBLE MEANS ALONG WITH
THE UKMET HAVE BEEN SHOWING A LESS AMPLIFIED RIDGE THAN MOST
RECENT GFS/GEFS MEAN SOLNS.  THE FLATTER RIDGE OF THE ECMWF
CLUSTER LEADS TO LESS SWWD ELONGATION OF DOWNSTREAM FLOW THAN
INDICATED BY THE GFS CLUSTER.  HOWEVER SOME GFS RUNS SUCH AS THE
12Z/19 AND 00Z/20 RUNS HAVE BEEN FAIRLY STRONG WITH THE WRN RIDGE
BUT STILL SHOWED MORE CONSOLIDATION OF ENERGY OVER THE PLAINS LIKE
THE ECMWF SCENARIO.  THE CANADIAN HAD BEEN IN THE ECMWF CLUSTER 24
HRS AGO BUT LATELY HAS TRENDED TOWARD THE GFS SCENARIO TO SOME
EXTENT.  EITHER SCENARIO STILL APPEARS PLAUSIBLE BUT PERSISTENCE
WITH SYSTEMS FLOWING ACROSS THE NRN PAC MAY FAVOR LEANING A LITTLE
MORE TOWARD THE ECMWF IDEA.

THESE DIFFS THAT DEVELOP BY EARLY NEXT WEEK PROPAGATE DOWNSTREAM
TO AFFECT SFC EVOLUTION ALONG THE GULF COAST AND THEN OVER THE
EAST COAST/WRN ATLC.  THE 06Z GFS IS THE MOST EXTREME SOLN WITH
SWWD ELONGATION ALOFT OVER THE WRN HALF OF THE CONUS AND FAST
EJECTION OF PLAINS ENERGY... SO IT IS FARTHEST OFFSHORE AT THE SFC
BY DAY 6 WED.  THE SEPARATION OF SWRN ENERGY IN THE 06Z GFS ALSO
LEADS TO ANOTHER GULF WAVE BY DAY 7 AS THAT ENERGY EJECTS EWD.
THE 00Z GFS COMPARES MUCH BETTER TO WHAT CONSENSUS EXISTS ALOFT
BUT ITS SFC SOLN OFF THE EAST COAST IS SIMILAR TO THE 06Z RUN.
EVEN WITH SOME MID LVL DIFFS THE 00Z ECMWF/CANADIAN END UP WITH A
SFC LOW OFF SRN NEW ENGLAND... ALBEIT WITH DIFFERENT STRENGTHS...
BY DAY 6 WED.  THIS SOLN IS CONSISTENT WITH YDAYS FCST.  AT THIS
TIME ENSEMBLE MEANS SHOW LOW PRESSURE JUST OFF THE EAST COAST BUT
THE SPREAD AMONG INDIVIDUAL MEMBERS IS SUFFICIENTLY GREAT TO KEEP
THE MEAN FCSTS FAIRLY WEAK.

BEHIND THIS SYSTEM THERE IS DECENT AGREEMENT ON ANOTHER SURGE OF
NRN STREAM ENERGY WHICH BY DAY 7 THU SHOULD BRING AN AREA OF WEAK
LOW PRESSURE AND TRAILING FRONT INTO THE E-CNTRL CONUS.  THE
GFS/ECMWF AND THEIR RESPECTIVE ENSEMBLE MEANS ALL SHOW BETTER THAN
AVERAGE CLUSTERING WITH THIS FEATURE AND SURROUNDING FLOW.

ABOVE CONSIDERATIONS GENERALLY FAVOR A CONSENSUS/BLEND APPROACH TO
ACCOUNT FOR LACK OF CONVERGENCE IN GUIDANCE EARLY-MID PERIOD AND
IMPROVED CLUSTERING THEREAFTER... WITH SOME CONSIDERATION FOR
CONTINUITY FROM YDAY.  TO REFLECT THESE IDEAS THE DAYS 3-5 SUN-TUE
FCST STARTS WITH A 50/30/20 BLEND OF THE 00Z ECMWF/UKMET/ECMWF
MEAN WITH DAYS 6-7 WED-THU ADJUSTING TO A 40/30/30 BLEND OF THE
ECMWF/ECMWF MEAN/GEFS MEAN.  



12Z UPDATE... NEW GUIDANCE INCLUDING THE ECMWF HAS COME INTO
BETTER AGREEMENT WITH DAY 3 SUN PLAINS EVOLUTION WITH A BETTER
DEFINED SFC REFLECTION THAN THE 00Z ECMWF.  THE FINAL FCST
INCORPORATES IDEAS FROM THE 12Z ECMWF/UKMET/CMC WITH THE GFS LESS
FAVORED AS IT IS ON THE DEEP SIDE OF THE SOLN SPREAD.  UNCERTAINTY
REMAINS ABOUT AS HIGH AS BEFORE FOR THE REST OF THE FCST.  THE
UKMET/CMC HAVE TRENDED TOWARD THE GFS SCENARIO OF PULLING A
SIGNIFICANT AMOUNT OF ENERGY SWWD INTO NWRN MEXICO BY DAY 5 TUE
THUS LEADING TO A MORE PROGRESSIVE/EWD WRN ATLC SYSTEM.  HOWEVER
THE 12Z ECMWF MAINTAINS CONTINUITY... ALBEIT IN SLIGHTLY SLOWER
FORM... TOWARD A MORE CONSOLIDATED NRN STREAM MID LVL SYSTEM THAT
ULTIMATELY MAINTAINS AN EAST COAST SFC LOW ON THE WRN EDGE OF THE
GUIDANCE SPREAD.  SOME TIMING/DETAIL DIFFS ARE NOTED WITH UPSTREAM
FEATURES WITH MORE DATA DESIRED BEFORE MAKING A CONFIDENT
ADJUSTMENT.  FOR DAYS 4-7 THE FULL EVALUATION OF LATEST SOLNS IN
LIGHT OF SENSITIVITY OF THE FCST PATTERN FAVORS ONLY MINOR DETAIL
ADJUSTMENTS TO THE UPDATED PRELIM ISSUANCE.



THE LARGE SCALE MEAN PATTERN SHOULD MAINTAIN WARM AND DRY CONDS
OVER MOST AREAS WEST OF THE ROCKIES AND BELOW NORMAL TEMPS OVER
THE ERN HALF OF THE LOWER 48.  THE MOST EXTREME READINGS ARE FCST
OVER THE NORTHEAST ON SUN-MON WHEN HIGHS MAY BE UP TO 15-25 F
BELOW NORMAL.  THERE IS STILL CONSIDERABLE UNCERTAINTY OVER THE
EVENTUAL NWD EXTENT OF WINTRY PCPN SPREADING EWD FROM THE PLAINS
SUN ONWARD... WITH POSSIBLE SCENARIOS OVER THE NORTHEAST BY
TUE-WED RANGING FROM A MAJOR EVENT TO NO PCPN AT ALL.  CURRENT
FCST PREFERENCES ARE TOWARD HAVING AT LEAST SOME PCPN REACHING
NERN AREAS.  MEANWHILE DEPENDING ON THE DEGREE OF GULF INFLOW
THERE MAY BE SOME LOCALLY MDT-HVY RNFL OVER EXTREME SRN AREAS.
BEHIND THIS SYSTEM SOME LOCATIONS FROM THE NRN ROCKIES INTO THE
GRTLKS/OH VALLEY MAY SEE ONE OR MORE DAYS OF LGT SNOW.  THOUGH A
LOW PROBABILITY SOLN AT THIS TIME... POTENTIAL EXISTS FOR SOME
RESIDUAL SRN STREAM ENERGY TO GENERATE ANOTHER GULF OF MEXICO WAVE
LATE IN THE PERIOD.

RAUSCH
43
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Heads up Fred - JAC, 1/20/2011, 1:12 pm
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