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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0636Z Mar 24, 2015)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 AM EDT TUE MAR 24 2015

VALID 12Z FRI MAR 27 2015 - 12Z TUE MAR 31 2015

...OVERVIEW...

LATEST GUIDANCE IS SUGGESTING THAT THE AMPLIFIED WRN RIDGE/ERN
TROUGH PATTERN FCST TO BE IN PLACE FOR MOST OF THE PERIOD MAY
BEGIN TO EVOLVE TOWARD FLATTER MEAN FLOW BY NEXT TUE.  WHILE SOME
EMBEDDED DETAILS WITHIN THE RIDGE/TROUGH CONFIGURATION HAVE BEEN
AND CONTINUE TO BE PROBLEMATIC... ENSEMBLE GUIDANCE AND THE LIKELY
TREND TOWARD FLATTER FLOW SUGGEST THAT OVERALL PREDICTABILITY OF
SIGNIFICANT FEATURES MAY DECLINE RAPIDLY AFTER EARLY NEXT WEEK.


...GUIDANCE EVALUATION AND PREFERENCES...

INTO DAY 6 MON THE MODELS AND ENSEMBLES MAINTAIN GOOD AGREEMENT
AND CONTINUITY WITH THE GENERAL THEMES OF THE FCST.  A SIGNIFICANT
PORTION OF ENERGY FROM A SPLITTING ERN PAC TROUGH SHOULD ROUND THE
WRN RIDGE AND RAPIDLY DESCEND INTO THE ERN MEAN TROUGH... KICKING
OUT THE DEEP TROUGH OVER THE EAST FROM LATE THIS WEEK INTO THE
WEEKEND.  REMAINING ERN PAC ENERGY MAY PROGRESS INTO THE WEST IN A
FORM YET TO BE DETERMINED.  THE PSBL FLATTENING OF THE MEAN
PATTERN MAY BE HERALDED BY UPSTREAM PAC ENERGY REACHING THE WEST
BY TUE WITH QUICKLY INCREASING SPREAD FOR DOWNSTREAM DETAILS.

ONE OF THE MOST PROBLEMATIC ASPECTS OF THE FCST HAS BEEN WITH ERN
PAC TROUGH ENERGY FCST TO SPLIT AROUND DAY 3 FRI... WITH GUIDANCE
HAVING DIFFICULTY IN DETERMINING THE RELATIVE PROPORTION OF ENERGY
ASSIGNED TO EACH STREAM AND THE FORM TAKEN BY THE SRN STREAM
ENERGY PSBLY MOVING INTO THE WEST.  THIS IS NOT SURPRISING GIVEN
THAT FLOW SEPARATION AND WEAK ENERGY PASSING THROUGH A MEAN RIDGE
BOTH TEND TO HAVE BELOW AVERAGE PREDICTABILITY.  THUS FAR MODELS
HAVE NOT HELD ONTO A CONSISTENT IDEA FOR THE RESULTING SRN STREAM
FEATURE FOR MORE THAN 24-36 HRS.  THE 18Z GFS/12Z ECMWF MAY BE A
LITTLE DEEP BUT AT LEAST COMPARE ACCEPTABLY TO THE ENSMEANS IN
PRINCIPLE... WITH THE 12Z ECMWF MEAN PERHAPS MOST APPEALING IN
SHOWING SOME DEFINITION TO THE SHRTWV BUT WITHOUT BEING AS STRONG
AS SOME OPERATIONAL RUNS.  AMONG 00Z RUNS THUS FAR THE GFS PULLS
THE SRN ENERGY FARTHER SWWD THAN OTHER SOLNS/ESTABLISHED CONSENSUS.

IN GENERAL THERE HAS BEEN BETTER CONTINUITY WITH THE FAIRLY
VIGOROUS SRN CANADA/NERN CONUS SYSTEM SUPPORTED BY THE NRN STREAM
COMPONENT OF THE SPLITTING ERN PAC TROUGH... ALLOWING FOR SOME
INCLUSION OF OPERATIONAL GUIDANCE THROUGH AT LEAST THE MIDDLE OF
THE PERIOD.  STILL THE INCONSISTENCY IN THE DETAILS OF THIS SYSTEM
HAVE LIKELY BEEN PLAYING A PART IN THE MULTI-DAY OSCILLATIONS FOR
THE FCST OF THE LEADING ERN CONUS TROUGH.  VARIATION IN THE DEGREE
OF SWWD ELONGATION AND TIMING OF SHRTWVS WITHIN THE INITIAL ERN
TROUGH HAVE LED TO INCONSISTENCY FOR THE DEFINITION/TIMING/TRACK
OF FRONTAL WAVINESS FROM THE EAST COAST INTO THE WRN ATLC. 
CURRENTLY THE TIMING IS IN THE MIDDLE TO FASTER HALF OF THE
MULTI-DAY SPREAD BUT NOT UNREASONABLE GIVEN THE FAST APPROACH OF
THE UPSTREAM ENERGY.

AS DAY 7 TUE SHRTWV ENERGY REACHES THE WEST... THERE HAS BEEN A
NOTICEABLE FASTER TREND OVER THE PAST DAY OR SO AND THE 18Z GEFS
MEAN BRINGS IN MORE HGT FALLS THAN THE 12Z VERSION.  AT LEAST
PREFER TO LEAN AWAY FROM THE 18Z GEFS MEAN FOR NOW GIVEN THE MEAN
RIDGE IN PLACE OVER THE WEST INTO THE START OF NEXT WEEK.

WITH VARIOUS ASPECTS OF THE 18Z GFS/12Z ECMWF ACCEPTABLY
COMPARABLE TO OTHER GUIDANCE... THEY WERE GIVEN EVEN OR SLIGHTLY
GREATER WEIGHTING VERSUS THE 12Z NAEFS/ECMWF MEANS INTO DAY 6 MON.
 QUESTIONABLE TIMING/AMPLITUDE OF THE 12Z ECMWF SHRTWV REACHING
THE WEST LATE IN THE PERIOD AND INCREASING PHASE DIFFS DOWNSTREAM
IN BOTH THE GFS AND ECMWF RECOMMENDED EXCLUSIVE USE OF THE 12Z
ECMWF/GEFS/NAEFS ENSEMBLE MEANS BY DAY 7 TUE.


...SENSIBLE WEATHER HIGHLIGHTS...

WITH THE DEPARTURE OF THE WAVY FRONT FROM THE EAST EXPECT A PERIOD
OF LOWER THAN AVG COVERAGE AND INTENSITY FOR PCPN ACROSS MOST OF
THE LOWER 48.  FROM FRI INTO THE WEEKEND THERE MAY BE SOME AREAS
OF LGT SNOW FROM THE CNTRL APLCHNS NEWD AS A COLD TROUGH ALOFT
CROSSES THE REGION.  THEN VIGOROUS LOW PRES TRACKING ACROSS SRN
CANADA SHOULD BRING BREEZY CONDS AND AN AREA OF SNOW N/RAIN S
ACROSS THE NERN QUADRANT OF THE CONUS FROM THE WEEKEND INTO THE
NEXT WEEK.  SHRTWV ENERGY ROUNDING THE WRN RIDGE MAY BRING A
PERIOD OF LGT PCPN TO EXTREME NRN PARTS OF THE WEST WITH A BREAK
UNTIL EARLY NEXT WEEK WHEN UPSTREAM ENERGY ARRIVES.  CONFIDENCE IS
LOW REGARDING ANY PCPN OVER REMAINING PARTS OF THE WEST... WITH
ONGOING DIFFS/POOR CONTINUITY FOR WEAK SRN STREAM ENERGY ALOFT. 
THERE MAY BE SOME INCREASE IN MSTR NEAR/INLAND FROM THE GULF COAST
BY THE LATTER HALF OF THE PERIOD BUT DETAILS ARE UNCERTAIN GIVEN
CURRENT SPREAD IN SPECIFICS OF FLOW ALOFT.

EXPECT VERY WARM TEMPS OVER THE WEST AND ON SOME DAYS INTO THE
NRN-CNTRL PLAINS WITH A BROAD AREA OF PLUS 10-25F ANOMALIES
EXPECTED.  GREATEST POTENTIAL FOR CALENDAR DAY RECORD HIGHS/WARM
LOWS SHOULD BE OVER THE WEST ON FRI-SAT.  MEANWHILE THE EAST WILL
SEE UNSEASONABLY CHILLY READINGS FRI-SAT WITH MINUS 10-20F
ANOMALIES.  ERN TEMPS SHOULD MODERATE THEREAFTER.

RAUSCH