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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0640Z 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
240 AM EDT SUN SEP 28 2014

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

...OVERVIEW...

LATEST MODEL/ENSEMBLE SOLNS DISPLAY BETTER THAN 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 FLOW.  MEANWHILE GUIDANCE FINALLY APPEARS TO BE
STARTING A TREND TOWARD A COMMON SCENARIO FOR THE RECENTLY
PROBLEMATIC TROUGH/UPR LOW NEAR THE EAST COAST AND ASSOC WRN ATLC
SFC EVOLUTION.


...GUIDANCE EVALUATION/PREFERENCES...

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 SHOULD DEEPEN
THIS WAVE SIGNIFICANTLY BY THE TIME IT REACHES WRN-UPR GRTLKS BY
DAY 5 FRI.  ASIDE FROM TYPICAL RUN TO RUN DIFFS THE GFS/ECMWF HAVE
BEEN SHOWING THIS IDEA FOR THE PAST COUPLE DAYS.  GRADUAL
DEEPENING OF THE TROUGH ALOFT IN THE ENSEMBLE MEANS LEADS TO A
CONSENSUS THAT IS 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.  THROUGH THE 18Z
CYCLE GOOD CLUSTERING IN PRINCIPLE FAVORED A COMPROMISE AMONG THE
12Z-18Z GFS/12Z ECMWF AND 18Z GEFS/12Z ECMWF ENSEMBLE MEANS.  THUS
FAR NEW 00Z GUIDANCE MAINTAINS SUPPORT FOR THIS APPROACH.

BY DAY 7 SUN UPSTREAM NRN PAC ENERGY FLOWING AROUND THE WRN RIDGE
IS FCST TO SUPPORT A SRN CANADA SFC WAVE AND WARM FRONT EXTENDING
INTO THE NRN TIER CONUS.  AS IS USUALLY THE CASE BY THAT TIME
FRAME THERE ARE SOME MEANINGFUL DETAIL DIFFS BUT THE
AFOREMENTIONED BLEND PROVIDES A GOOD INTERMEDIATE SOLN.  THE NEW
00Z GFS IS SLIGHTLY FASTER THAN MOST OTHER SOLNS.

ALONG THE EAST COAST... AT LEAST INTO EARLY DAY 4 THU THE NEW 00Z
GUIDANCE IS SHOWING THE BEST AGREEMENT YET FOR THE TROUGH/UPR LOW
FCST TO DRIFT THROUGH THE LONGWAVE MEAN RIDGE.  SOLNS DIVERGE
SOMEWHAT THEREAFTER.  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
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. 
A BRIEF PERIOD OF ATLC INFLOW COULD 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.

RAUSCH