Prognostic Meteorological Discussion
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000
FXUS02 KWBC 271559
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1059 AM EST SAT DEC 27 2014

VALID 12Z TUE DEC 30 2014 - 12Z SAT JAN 03 2015

...OVERVIEW...

LATEST GUIDANCE CONTINUES TO SHOW A LIKELY RETROGRESSION OF THE
NRN PART OF THE ERN PAC/NWRN NOAM MEAN RIDGE... WITH MULTI-DAY
MEANS MIGRATING THE ASSOC CORE OF POSITIVE HGT ANOMALIES FROM JUST
OFF THE AK PANHANDLE TO EXTREME NWRN MAINLAND AK.  TELECONNECTIONS
RELATIVE TO THIS HGT ANOMALY CENTER SAY THAT THE WRN CONUS PART OF
THE MEAN TROUGH EXTENDING SWWD FROM NERN CANADA SHOULD FLATTEN
THUS ALLOWING FOR MODERATING TEMPS OVER CA AND THE
GRTBASIN/SOUTHWEST.  ELSEWHERE TELECONS INDICATE LESS CHANGE ON A
MULTI-DAY BASIS WITH COLD TEMPS PERSISTING ACROSS NRN AREAS AND
SWD OVER THE PLAINS... AND WARMEST TEMPS CONFINED TO THE EXTREME
SOUTHEAST.


...GUIDANCE EVALUATION/PREFERENCES...

WITHIN THE EVOLVING MEAN PATTERN THE PRIMARY FEATURE OF INTEREST
CONTINUES TO BE THE UPR LOW WHICH NEARLY ALL GUIDANCE CLOSES OFF
OVER/NEAR CA AND THEN EJECTS EWD AS UPSTREAM ENERGY ROUNDING THE
UPSTREAM RIDGE SHOULD APPROACH/REACH THE NORTHWEST BY NEXT
FRI/SAT.  THERE CONTINUES TO BE A FAIR AMOUNT OF MODEL/ENSEMBLE
SPREAD REGARDING THE TIMING AND TO A SOMEWHAT LESSER DEGREE TRACK
OF THE UPR LOW.  WITH SOME CYCLE TO CYCLE ADJUSTMENTS SEEN IN MOST
SOLNS AN INTERMEDIATE MULTI-RUN AVG WOULD LIKELY PROVIDE THE BEST
OPTION.  IN PARTICULAR THIS APPROACH WOULD LEAN AWAY FROM THE 00Z
UKMET/CMC... WHICH IN DIFFERING WAYS TRACK THE UPR LOW FARTHER WWD
ALONG THE CA COAST... AND LATEST OPERATIONAL/PARALLEL GFS RUNS
THAT TEND TO BE ON THE FASTER SIDE OF THE SPREAD.  OVERALL
CONFIDENCE IS AVG AT BEST BUT IS IMPROVED SOME WITH THE ARRIVAL OF
THE 06Z GEFS MEAN THAT IS VERY CLOSE TO THE 00Z ECMWF MEAN AS WELL
AS THE OPERATIONAL 00Z ECMWF INTO EARLY DAY 6 FRI.  FROM LATER FRI
ONWARD THE 00Z ECMWF MAY BE TOO AMPLIFIED WITH THE EJECTING UPR
TROUGH GIVEN THE ENSEMBLE ENVELOPE AND ACCELERATING SWLY MEAN FLOW
ALOFT.  THUS THE PREFERRED BLEND INCORPORATES THE 00Z ECMWF RUN
ALONG WITH THE 06Z GEFS/00Z ECMWF MEANS THROUGH EARLY FRI.

BY DAY 7 SAT AN ADDED QUESTION MARK WILL BE THE EXTENT TO WHICH
NRN STREAM FLOW INTERACTS WITH THE EJECTING SWRN SYSTEM.  THIS
UNCERTAINTY IS REFLECTED IN THE DIFFERENT SFC SOLNS OVER THE
CNTRL-ERN STATES AT THAT TIME... RANGING FROM A WEAK N-S ELONGATED
SYSTEM AS IN THE 00Z ECMWF TO A DEEP LOW CROSSING THE GRTLKS
AND/OR NEW ENGLAND AS IN THE 06Z GFS AND 12Z/26 ECMWF RUNS.
00Z-06Z ENSEMBLES GENERALLY INCLUDE THIS RANGE OF SOLNS ASIDE FROM
DEPTH AS STRONG AS THE 06Z GFS.  HIGH SPREAD/LOW CONFIDENCE IN
SPECIFICS FAVORS AN ENSEMBLE MEAN APPROACH BY DAY 7.  THE
SIMILARITY OF THE 06Z GEFS MEAN TO THE OLD 12Z ECMWF MEAN SFC
PATTERN ALLOWS A BLEND OF THE 06Z GEFS/00Z ECMWF MEAN TO YIELD A
GOOD INTERMEDIATE SOLN FOR THE NWD EXTENT OF LOWER SFC PRESSURES.


....SENSIBLE WEATHER HIGHLIGHTS...

THE MOST ACTIVE WEATHER DURING THE PERIOD SHOULD BE ASSOC WITH THE
UPR LOW FCST TO CLOSE OFF OVER CA AND THEN EJECT EWD AFTER THU.
THIS SYSTEM SHOULD BRING SNOW LVLS TO UNUSUALLY LOW ELEVS AT SOME
LOCATIONS OVER THE SWRN STATES WITH BEST PCPN TOTALS OVER FAVORED
TERRAIN.  FARTHER EWD EXPECT MSTR TO SURGE NEWD FROM THE WRN GULF
COAST REGION STARTING AROUND THU-FRI... DEPENDING ON TIMING OF UPR
LOW PROGRESSION.  BY THE LATTER HALF OF THE PERIOD MODEL/ENSEMBLE
GUIDANCE INDICATES THE BEST POTENTIAL FOR LOCALLY HVY RNFL FROM
EXTREME ERN TX INTO TN/GA.  SOME DISTANCE NWWD OF THE HVY RAIN
AREA TEMPS SHOULD BE COLD ENOUGH FOR WINTRY PCPN TYPES.
PLACEMENT/INTENSITY OF SNOW AND A PSBL TRANSITION ZONE WILL BE
VERY DEPENDENT ON THE ULTIMATE SFC EVOLUTION BY NEXT FRI-SAT.
ACROSS NRN AREAS ANTICIPATE PERIODS OF LAKE EFFECT SNOW AND
ELSEWHERE ONE OR MORE PERIODS OF SNOW THAT MAY ACCOMPANY A COUPLE
FRONTAL BOUNDARIES.

GREATEST ANOMALIES FOR TEMPS SHOULD BE OVER THE CNTRL HIGH PLAINS
ON TUE WITH SOME HIGH TEMPS 30-40F BELOW NORMAL AS THE AREA
EXPERIENCES UPSLOPE SNOWFALL.  TEMPS SHOULD MODERATE AFTER TUE
EXCEPT OVER THE GRTBASIN/SOUTHWEST WHERE THE FCST UPR LOW MAY
BRING MULTIPLE DAYS WITH HIGHS 10-20F BELOW NORMAL.  AHEAD OF
DEVELOPING CNTRL CONUS LOW PRESSURE BY NEXT SAT... READINGS AT
THAT TIME SHOULD TREND ABOVE TO WELL ABOVE NORMAL WITH GREATEST
ANOMALIES MOSTLY LIKELY TO BE FOR MIN TEMPS OVER THE SOUTHEAST.

RAUSCH

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