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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0634Z Aug 27, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 AM EDT WED AUG 27 2014

VALID 12Z SAT AUG 30 2014 - 12Z WED SEP 03 2014

...OVERVIEW AND PREFERENCES...

EXPECT FAIRLY HIGH HGTS ALOFT... ANCHORED BY RIDGING OVER THE
SOUTHEAST... TO PREVAIL OVER THE EAST.  A TROUGH PROGRESSING FROM
THE WEST AND ACROSS THE NRN HALF OF THE PLAINS FOLLOWED BY
UPSTREAM ENERGY THAT COULD REACH THE NORTHWEST LATE IN THE PERIOD
WILL SUPPORT LOWER HGTS OVER THIS AREA.  MOST FEATURES CURRENTLY
EXHIBIT SOME MEANINGFUL SPREAD AND/OR CONTINUITY ADJUSTMENTS WITH
A 70/30 BLEND OF THE 12Z ECMWF MEAN/18Z GEFS MEAN CAPTURING THE
BEST COMBINATION OF RECENT TRENDS AND INTERMEDIATE POSITIONING OF
FEATURES RELATIVE TO THE FULL GUIDANCE SPREAD.


...GUIDANCE EVALUATION...

IN PRINCIPLE THERE HAS BEEN DECENT CLUSTERING/CONTINUITY WITH THE
UPR TROUGH REACHING THE WEST EARLY IN THE WEEKEND AND CONTINUING
INTO THE PLAINS EARLY NEXT WEEK... THOUGH SHRTWV DETAIL DIFFS IN
THE OPERATIONAL RUNS CONTINUE TO RESULT IN SPREAD FOR THE TIMING
OF THE LEADING SFC FRONT.  PREFER TO RELY ON THE ENSEMBLE MEANS
UNTIL THE OPERATIONAL SOLNS BEGIN TO SETTLE ON THE DETAILS. 

AS SEEN YDAY MODEL/ENSEMBLE SPREAD BEGINS TO WIDEN CONSIDERABLY
FROM THE NRN PAC INTO NWRN CONUS LATE IN THE PERIOD.  THIS
ORIGINATES FROM DIVERGING OPINIONS ON THE HANDLING OF ENERGY
WITHIN A SRN BERING SEA INTO NRN PAC TROUGH AS OF DAY 4 SUN.  BY
DAY 7 WED THE MOST LIKELY SCENARIO IS FOR SOME DEGREE OF TROUGHING
TO REACH THE PAC NW ALBEIT WITHIN A FULL ENSEMBLE SPREAD THAT
INCLUDES ANY SCENARIO FROM A TROUGH TO A RIDGE.  THE 12Z CMC MEAN
SUPPORTS THE 12Z ECMWF MEAN THAT KEEPS THE TROUGH LESS AMPLIFIED
THAN THE 18Z GEFS MEAN... BUT NOTE THAT EVEN THE LATTER IS MODEST
RELATIVE TO THE 18Z GFS/12Z CMC.

GUIDANCE IS STILL IN THE PROCESS OF RESOLVING THE SFC DETAILS
AHEAD OF THE SHRTWV FCST TO TRACK NEWD FROM THE ERN PLAINS/MS VLY.
 OVER THE PAST 12-24 HRS LATEST GUIDANCE HAS GRAVITATED RATHER FAR
NWD WITH THE SFC WAVE TRACKING THROUGH THE GRTLKS AROUND DAY 4 SUN
AND WITH THE LEADING FRONT... SO THE UPDATED FCST REFLECTS THIS
ADJUSTMENT IN FRONTAL POSN AND CORRESPONDING TEMPS.  CONFIDENCE IS
STILL MODERATE AT BEST DUE TO SOME DEPENDENCE ON DIFFICULT TO
RESOLVE SMALLER SCALE DETAILS.  WITH THE SHRTWV ALOFT RECENT GFS
RUNS HAVE TENDED BE IN THE FASTER PORTION OF THE ENVELOPE.


...SENSIBLE WEATHER HIGHLIGHTS...

SYSTEM CROSSING THE WEST WILL SUPPORT AREAS OF RNFL ACROSS NRN
PARTS OF THE REGION... WITH THE LEADING FRONT THEN SUPPORTING A
BAND OF LOCALLY HVY CONVECTION FROM THE NRN PLAINS EWD/SEWD.  ALSO
EXPECT A FAIRLY BROAD AREA OF 5-15F BELOW NORMAL MAX TEMPS TO
EXTEND FROM THE NORTHWEST INTO THE NRN PLAINS WITH SOME MODERATION
LATER IN THE PERIOD.  FARTHER EWD MOIST FLOW AHEAD OF THE MID LVL
SHRTWV TRACKING NEWD FROM THE ERN PLAINS/MS VLY AS WELL AS
INTERACTION WITH THE SFC WAVE/FRONT OVER NRN PARTS OF THE EAST
WILL PROVIDE SOME ENHANCEMENT TO RNFL... WITH HIGHEST TOTALS MOST
LIKELY TO BE W OF THE APLCHNS AND FROM THE MID-UPR MS VLY INTO THE
NORTHEAST.  MAX TEMPS MAY REACH 10F OR SO ABOVE NORMAL FROM THE OH
VLY INTO NRN MID ATLC/SRN NEW ENGLAND DURING THE WEEKEND WITH THE
SOUTHEAST/MID ATLC MOST CONSISTENTLY ABOVE NORMAL THROUGH THE
PERIOD.

RAUSCH