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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0644Z Apr 13, 2014)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT SUN APR 13 2014

VALID 12Z WED APR 16 2014 - 12Z SUN APR 20 2014

...OVERVIEW AND PREFERENCES...

THE MOST PROMINENT FEATURE OF THE MEDIUM RANGE PERIOD WILL BE A
TROUGH ALOFT PROGRESSING ACROSS THE LOWER 48.  GUIDANCE HAS BEEN
INDICATING MULTIPLE UNCERTAINTIES WITH THIS FEATURE INCLUDING
DISTRIBUTION OF ENERGY WITHIN THE TROUGH DURING THE FIRST HALF OF
THE PERIOD... EVENTUAL INFLUENCE OF UPSTREAM PAC ENERGY FEEDING
INTO THE OVERALL TROUGH AS IT REACHES THE ERN HALF OF THE CONUS...
AND TIMING OF THE TROUGH.  IN THE WAKE OF THE SHRTWV ENERGY
BRUSHING THE NW AROUND FRI MODELS/ENSEMBLES HAVE GENERALLY BEEN
INDICATING ESTABLISHMENT OF A BROAD ERN PAC MEAN TROUGH AND WRN
NOAM MEAN RIDGE.  MEANWHILE STRENGTH AND TIMING DIFFS EXIST FOR A
SRN STREAM ERN PAC TROUGH/UPR LOW THAT MAY HEAD INTO THE SWRN
CONUS/NRN MEXICO IN THE LATTER HALF OF THE FCST.

ESPECIALLY FOR THE CONUS TROUGH AND ASSOC SFC EVOLUTION THERE HAS
BEEN SOME TRENDING TOWARD AN INTERMEDIATE SOLN... AS ENSEMBLE
MEANS GAIN DEFINITION TOWARD AN AVG OF RECENT OPERATIONAL GUIDANCE
AND SOME OF THE MORE EXTREME MODEL SOLNS ADJUST THE OTHER WAY. 
ALBEIT WITH A SOMEWHAT FASTER ADJUSTMENT FROM CONTINUITY THE 18Z
GFS/12Z ECMWF AND THEIR RESPECTIVE ENSEMBLE MEANS OFFER THE BEST
WAY TO INCLUDE IDEAS FROM BOTH SETS OF GUIDANCE DAYS 3-7
WED-SUN... WITH SLIGHTLY MORE WEIGHTING ON THE MEANS GIVEN
CONTINUED DETAIL UNCERTAINTY.


...GUIDANCE EVALUATION...

WITHIN THE OVERALL CONUS TROUGH MODELS/ENSEMBLES ARE STILL SHOWING
GREATER THAN DESIRED SPREAD WITH HOW ENERGY NEAR THE US-CANADIAN
BORDER WILL EVOLVE... LEADING TO SFC DIFFS FROM THE N-CNTRL PLAINS
INTO THE UPR GRTLKS WED-THU.  SOMEWHAT COMPLEX CANADIAN PATTERN
WITH A WEAKENING UPR HIGH DESCENDING FROM NRN CANADA BEHIND THE
ENERGY OF INTEREST SUGGESTS IT MAY STILL TAKE SOME TIME TO RESOLVE
THIS ASPECT OF THE FCST.  LATEST GFS RUNS HAVE TRENDED TOWARD
MULTIPLE ECMWF RUNS THAT HAVE BEEN TRACKING A WAVE NEWD FROM THE
NRN PLAINS WITH ENSEMBLE MEANS INCREASINGLY HINTING AT SUCH AN
EVOLUTION AS WELL SO THE PREFERRED BLEND IS THE MOST APPEALING
OPTION AT THIS TIME.  MEANWHILE THERE IS A FAIR AMOUNT OF SPREAD
AMONG INDIVIDUAL ENSEMBLE MEMBERS WITH THE WRN CONUS INTO PLAINS
TROUGH DURING THE FIRST HALF OF THE FCST... BUT THE OVERALL
GEFS/ECMWF MEANS AND MOST OPERATIONAL RUNS ARE FAIRLY WELL
CLUSTERED.  THIS CONSENSUS AND TRENDS OVER THE PAST 2-3 DAYS DO
NOT OFFER A LOT OF SUPPORT FOR SOME GEFS/CMC MEMBERS THAT WANT TO
HOLD THE TROUGH FARTHER WWD IN THIS TIME FRAME.

THE ISSUES SEEN WED-THU REDUCE CONFIDENCE IN FCST DETAILS FROM FRI
ONWARD AS THE TROUGH ALOFT MOVES INTO THE EAST.  WHILE NOT A
STEADY TREND THE ENSEMBLE GUIDANCE SEEMS TO BE HEADING TOWARD
SOMEWHAT FASTER PROGRESSION WHICH IS A SCENARIO THAT SOME
ECMWF/GFS RUNS HAVE BEEN SUGGESTING IN THE PAST COUPLE DAYS.  IT
IS PSBL THAT PAC ENERGY ENTERING WRN NOAM ON FRI COULD ULTIMATELY
HELP TO EJECT SOME OF THE LEADING TROUGH ENERGY SO THE 18Z GFS/12Z
ECMWF RUNS THAT BRING LOW PRESSURE INTO THE NORTHEAST BY NEXT
WEEKEND MERIT SOME INCLUSION IN THE FCST BLEND.

ELSEWHERE... AHEAD OF THE BROAD TROUGHING BECOMING ESTABLISHED
OVER THE ERN PAC THERE IS FAIRLY GOOD AGREEMENT REGARDING A
VIGOROUS NERN PAC SYSTEM PUSHING A FRONT INTO THE NW DURING NEXT
WEEKEND.  WITH THE SRN STREAM ERN PAC FEATURE HEADING TOWARD THE
SWRN STATES/NRN MEXICO... GFS RUNS ARE ON THE COMBINED
FASTER/STRONGER SIDE OF THE GUIDANCE SPREAD AND THUS BY NEXT
WEEKEND GENERATE RNFL OVER/NEAR THE SRN PLAINS EARLIER THAN
CONSENSUS.


...SENSIBLE WEATHER HIGHLIGHTS...

SOME SNOW IS PSBL FROM THE NRN-CNTRL ROCKIES INTO THE UPR
GRTLKS... WITH INTENSITY/DURATION TO BE DETERMINED BY DETAILS OF
EVOLUTION SFC/ALOFT.  DURING WED-THU EXPECT DAYTIME HIGHS TO BE
10-25F BELOW NORMAL OVER THIS REGION WITH MODERATION THEREAFTER. 
IN THE WARMER AIR TO THE S AND E... DISPLACING CHILLY AIR
INITIALLY OVER THE E... EXPECT A BROADENING SHIELD OF MSTR TO
EXTEND FROM THE PLAINS INTO THE NORTHEAST WITH SOME LOCALLY
ENHANCED RNFL PSBL.  BEHIND THE ROCKIES TO ERN CONUS SYSTEM AN
INCOMING PAC SHRTWV WILL SUPPORT A PERIOD OF PCPN OVER THE PAC
NW/NRN ROCKIES THU-FRI WITH MORE ACTIVITY LIKELY AS A FRONT HEADS
INTO THE REGION DURING THE WEEKEND.  CNTRL/SRN PARTS OF THE WEST
SHOULD BE MOSTLY DRY... ASSUMING A WEAKER SRN STREAM ERN PAC UPR
SYSTEM THAN IN RECENT GFS RUNS... WITH TEMPS REACHING AT LEAST
10-15F ABOVE NORMAL OVER SOME AREAS BY LATE IN THE PERIOD.  

RAUSCH