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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1448Z Sep 21, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1048 AM EDT SUN SEP 21 2014

VALID 12Z WED SEP 24 2014 - 12Z SUN SEP 28 2014

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

ESPECIALLY WITH THE ARRIVAL OF THE 00Z UKMET/CMC IT APPEARS
GUIDANCE IS FINALLY DEVELOPING SOME DEGREE OF CONSENSUS WITH THE
AMPLIFIED ERN PAC TROUGH APPROACHING/MOVING INTO THE WEST DURING
THE PERIOD.  DOWNSTREAM THERE CONTINUES TO BE GOOD AGREEMENT UPON
RATHER HIGH HGTS IN GENERAL WITH A CORE OF POSITIVE HGT ANOMALIES
CENTERED OVER ONTARIO... THOUGH SMALLER SCALE WEAKNESSES TYPICALLY
MORE DIFFICULT TO RESOLVE MORE THAN 2-3 DAYS OUT WILL HAVE SOME
INFLUENCE ON SENSIBLE WEATHER OVER PARTS OF THE CNTRL-ERN STATES.

FOR ABOUT THE FIRST HALF OF THE FCST THERE IS SUFFICIENTLY LOW
SPREAD WITH THE ERN PAC TROUGH AND LACK OF CONFIDENCE WITH
SPECIFICS OF WEAKNESSES ALOFT OVER THE CNTRL/ERN STATES TO
RECOMMEND A CONSENSUS BLEND THAT IS PRIMARILY WEIGHTED TOWARD THE
00Z GFS/ECMWF AND CONTINUITY DAY 3 WED AND INCORPORATES HIGHER
AMTS OF THE GLOBAL ENSEMBLE MEANS WITH TIME INTO DAY 5 FRI...WITH
SLIGHTLY HIGHER CONFIDENCE IN THE MORE DETAILED ECMWF ENSEMBLE
MEANS OVER THE GEFS MEAN.

BY DAYS 6-7 SAT-SUN THE PRIMARY FCST ISSUES INVOLVE THE TIMING OF
THE ERN PAC/WRN CONUS TROUGH AND THE DEGREE OF FLOW SEPARATION
WITHIN THIS TROUGH.  AMONG LATEST GUIDANCE THE GFS/GEFS RUNS ARE
SOMEWHAT ON THE FAST SIDE OF THE SPREAD AND PROBABLY WORTH
ADJUSTING SOMEWHAT SLOWER IN LIGHT OF BIASES AND AGREED UPON
RIDGING DOWNSTREAM... BUT STILL MERIT SOME WEIGHTING AS THEY HAVE
BEEN MORE STABLE OVER THE PAST COUPLE DAYS.  THE 00Z CMC ALSO
CATCHES UP TO THE 00Z GEFS MEAN BY DAY 7 SUN.  ON THE OTHER HAND
THE 12Z ECMWF FROM YESTERDAY LINGERS ON THE SLOWER SIDE BUT THEN
SPEEDS UP IN THE 00Z RUN.  MEANWHILE OPERATIONAL MODELS HAVE BEEN
INDICATING SOMEWHAT GREATER POTENTIAL FOR AN UPR LOW TO CLOSE OFF
WITHIN THE TROUGH VERSUS THE TYPICALLY MORE PHASED ENSEMBLE MEANS.
 AT SOME FCST HRS RECENT GEFS MEANS HAVE DEPICTED GREATER
SEPARATION THAN THE 12Z ECMWF MEAN.  ULTIMATELY FAVORED NEARLY
EVEN WEIGHTING OF THE MOST RECENT GLOBAL ENSEMBLE MEANS TO ACCOUNT
FOR TIMING/SEPARATION CONSIDERATIONS.  BROKEN DOWN BY
REGION...PREFER SLIGHTLY GREATER WEIGHTING TOWARD THE ECMWF
ENSEMBLE MEAN ACROSS THE WEST...THE ECMWF ENSEMBLE MEAN ALMOST
EXCLUSIVELY ACROSS THE SOUTHEAST DAYS 3-4...AND THE GEFS MEAN
ACROSS THE NORTHEAST/NEW ENGLAND FOR DAYS 6/7.

...SENSIBLE WEATHER HIGHLIGHTS...

THE ERN PAC TROUGH MOVING INTO THE WEST SHOULD BRING A PRONOUNCED
COOLING TREND TO THE REGION WITH MSTR SPREADING INLAND AFTER
FOCUSING A NARROW BAND OF ENHANCED RNFL ALONG THE PAC NW/NRN CA
COAST ON WED.  AHEAD OF THIS SYSTEM... PCPN ASSOC WITH A WEAKNESS
ALOFT OVER THE PLAINS SHOULD TREND LIGHTER/MORE SCT WITH TIME. 
THE NRN TIER SHOULD SEE WELL ABOVE NORMAL TEMPS... WITH MULTIPLE
DAYS OF PLUS 10-20F ANOMALIES FOR MIN/MAX READINGS FROM THE NRN
ROCKIES INTO THE UPR MS VLY.  THE PRECISE EVOLUTION OF A WEAKNESS
ALOFT OVER THE SE/APLCHNS/MID ATLC WILL INFLUENCE THE NWD/INLAND
EXTENT OF RNFL... SOME LOCALLY HVY... EXPECTED NEAR THE SERN COAST
AND PSBLY INTO THE MID ATLC.  LOW PREDICTABILITY OF SUCH A
WEAK/SMALL SCALE FEATURE ARGUES FOR LOW PREDICTABILITY AND
THEREFORE CONFIDENCE AT THIS TIME.  ALSO EXPECT MOIST ELY LOW LVL
FLOW TO SUPPORT PERIODS OF RNFL OVER FL AND PORTIONS OF THE GULF
COAST.  DEPENDING ON EXACT EVOLUTION ALOFT MSTR ALONG COASTAL
AREAS MAY TRY TO SPREAD A LITTLE FARTHER INLAND OVER THE SOUTHEAST
LATE IN THE PERIOD.

RAUSCH/JAMES