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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1617Z Sep 28, 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
1217 PM EDT SUN SEP 28 2014

VALID 12Z WED OCT 01 2014 - 12Z SUN OCT 05 2014

...OVERVIEW...

MODEL/ENSEMBLE SOLNS DISPLAY AT LEAST AVG CLUSTERING/CONTINUITY IN
THE LARGE SCALE... WITH AN AMPLIFIED/DEEP AND SLIGHTLY NEGATIVELY
TILTED TROUGH PROGRESSING FROM THE W-CENTRAL STATES TO A POSN
COVERING THE ERN HALF OF THE CONUS BY LATE IN THE WEEKEND.  THIS
TROUGH WILL PUSH A WAVY COLD FRONT FROM THE PLAINS TO EAST COAST. 
AT THE SAME TIME FAIRLY STRONG UPSTREAM RIDGING ALOFT WILL BUILD
OVER THE WEST.  THIS AMPLIFIED PATTERN COULD BE ENHANCED DEPENDING
ON HOW WRN PAC T.S. KAMMURI INTERACTS WITH SURROUNDING/DOWNSTREAM
FLOW.  MEANWHILE GUIDANCE FINALLY APPEARS TO BE STARTING A TREND
TOWARD A COMMON SCENARIO FOR THE RECENTLY PROBLEMATIC LEAD
TROUGH/UPR LOW NEAR THE EAST COAST AND TO A LESSER EXTENT AN ASSOC
WRN ATLC SFC LOW EVOLUTION.


...GUIDANCE EVALUATION/PREFERENCES...

WPC MED RANGE GUIDANCE WAS PRIMARILY DERIVED FROM A BLEND OF
COMPATABLE GUIDANCE FROM THE 06 UTC GFS ENSEMBLE MEAN AND 00 UTC
ECMWF/NAEFS ENSEMBLE MEANS ALONG WITH WPC CONTINUITY.

WITHIN THE W-CNTRL TO ERN CONUS MEAN TROUGH... WRN CONUS TO PLAINS
SHRTWV ENERGY DAYS 3-4 WED-THU IS FCST TO DEVELOP A S-CNTRL PLAINS
WAVE THAT LIFTS NEWD.  MOST OPERATIONAL SOLNS THEN SUGGEST THAT
AMPLIFYING WRN CANADA ENERGY IMMEDIATELY UPSTREAM MAY DEEPEN THIS
WAVE SIGNIFICANTLY BY THE TIME IT REACHES WRN-UPR GRT LKS BY DAY 5
FRI.  ASIDE FROM PROBLEMATIC RUN TO RUN DIFFS...THE GFS/ECMWF HAVE
BEEN SHOWING THIS IDEA FOR THE PAST COUPLE DAYS AND BLENDING OF
THE ENSEMBLES RESULTED IN A LESS DEEP LOW AMID UNCERTAINTY. 
GRADUAL DEEPENING OF THE TROUGH ALOFT IN THE ENSEMBLE MEANS LEADS
TO A CONSENSUS THAT IS ALSO A TAD FASTER WITH THE FRONT TRAILING
FROM THIS SFC LOW DURING THE LATTER HALF OF THE PERIOD.  DEPENDING
ON EXACTLY HOW SHRTWV ENERGY EVOLVES THERE COULD ALSO BE A WEAK
FRONTAL WAVE NEAR THE EAST COAST BY NEXT SUN. OUR PREFERENCE FOR
THE ENSEMBLE MEANS SUGGESTS MINIMAL SUPPORT OF THE 00 UTC ECMWF
THAT HAS BROKEN RUN TO RUN CONTINUITY WITH A MORE PROGRESSIVE/LESS
AMPLIFIED MID-UPPER LEVEL TROUGHING AND PATTERN BY THEN.

BY DAY 7 SUN UPSTREAM NRN PAC ENERGY FLOWING AROUND THE WRN RIDGE
IS FCST TO SUPPORT A S-CENTRAL CANADAIAN SFC WAVE AND WARM FRONT
EXTENDING INTO THE N-CENTRAL US.  AS IS USUALLY THE CASE BY THAT
TIME FRAME THERE ARE SOME MEANINGFUL DETAIL DIFFS BUT THE
AFOREMENTIONED BLEND PROVIDES A GOOD INTERMEDIATE SOLN.

ALONG THE EAST COAST...INTO EARLY DAY 4 THU GUIDANCE IS SHOWING
MODEST AGREEMENT FOR THE TROUGH/UPR LOW FCST TO DRIFT THROUGH THE
LONGWAVE MEAN RIDGE.  SOLNS DIVERGE MORE OVER TIME.  THIS REMAINS
A DIFFICULT FCST GIVEN TYPICAL DIFFICULTIES OF RESOLVING WEAK
ENERGY WITHIN A MEAN RIDGE.  IN PARTICULAR WILL HAVE TO WATCH THE
STRENGTH OF RIDGING SFC/ALOFT OVER THE CANADIAN MARITIMES... IF
SUFFICIENT IT COULD LEAD TO A LINGERING SYSTEM AND EVEN A BRIEF
PERIOD OF  RETROGRESSION FOR THE SYSTEM OF INTEREST. 
 

...SENSIBLE WEATHER HIGHLIGHTS...

ALONG THE SFC FRONT CROSSING THE ERN HALF OF THE CONUS... EXPECT
THE BEST POTENTIAL FOR HEAVIEST RNFL FROM THE ERN PLAINS/MS VLY
INTO THE WRN-UPR GRTLKS IN ASSOC WITH STRONGEST DYNAMICS ALOFT/SFC
WAVE DEVELOPMENT ALONG WITH SOME INPUT OF MSTR FROM GULF INFLOW. 
SPC IS ALSO OUTLOOKING AN ASSOCIATED THREAT FOR SEVERE WEATHER
INVOF OK/KS/MO WED INTO THU. A BRIEF PERIOD OF ATLC INFLOW COULD
THEN ALSO ENHANCE AMTS OVER THE NORTHEAST LATE IN THE PERIOD BUT
TO WHAT EXTENT WILL DEPEND ON SPEED OF THE FRONT.  MEANWHILE THE
FRONT EXTENDING FROM THE WRN ATLC SYSTEM MAY FOCUS RNFL OVER
FLORIDA AND ELY LOW LVL FLOW MAY SUPPORT RNFL OVER SRN TX FOR A
TIME.  BY THE END OF THE FCST PERIOD THE LARGE SCALE PATTERN...
PERHAPS MORE REMINISCENT OF WINTER... SHOULD YIELD AN UNUSUALLY
LARGE AREA OF DRY WEATHER ACROSS THE LOWER 48.  COLDEST ANOMALIES
FOR DAYTIME TEMPS SHOULD FOLLOW THE CORE OF THE UPR TROUGH AND BE
MOST PRONOUNCED DAYS 3-5 WED-FRI WITH READINGS 10-15F BELOW NORMAL
FROM PARTS OF THE GRTBASIN/ROCKIES INTO THE NRN PLAINS.  EXPECT A
BROAD AREA OF MIN TEMPS 10-20F ABOVE NORMAL IN THE WARM SECTOR
AHEAD OF THE COLD FRONT WITH LESS EXTREME ANOMALIES FOR HIGHS. 
AFTER A COOL START TO THE PERIOD... WRN LOCATIONS WILL SEE A TREND
TO ABOVE NORMAL TEMPS AS RIDGING ALOFT BUILDS INTO THE REGION.

SCHICHTEL