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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Nov 22, 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
1058 AM EST SAT NOV 22 2014

VALID 12Z TUE NOV 25 2014 - 12Z SAT NOV 29 2014

...OVERVIEW...

GUIDANCE IS MAINTAINING A DECENT LEVEL OF AGREEMENT TOWARD THE
IDEA THAT THE COMBINATION OF A STRONG WEST COAST RIDGE INTO
MID-PERIOD AND RIDGING ALSO BUILDING OVER ALASKA AND VICINITY WILL
KEEP UPR TROUGHING AND BELOW NORMAL TEMPS OVER THE ERN HALF OF THE
CONUS FOR MOST OF THE PERIOD.  HOWEVER MEANINGFUL SHRTWV DETAIL
DIFFS STILL TEMPER CONFIDENCE IN THE EXACT SFC EVOLUTION OVER SOME
AREAS.  ALSO UP FOR CONTINUED DEBATE IS THE ULTIMATE EVOLUTION OF
ERN PAC TROUGH ENERGY AS IT APPROACHES/REACHES THE WEST COAST
TOWARD THE END OF NEXT WEEK.  THUS THE FULL MODEL/ENSEMBLE SPREAD
IS STILL GREATER THAN DESIRED FOR MOST OF THE FCST. 


...GUIDANCE EVALUATION/PREFERENCES...

ERN PAC TROUGH SEPARATION FCST BY TUE... NOW IN THE SHORT RANGE...
CONTINUES TO BE A SIGNIFICANT SOURCE OF SPREAD DOWNSTREAM.  ONCE
THE NRN PAC ENERGY REACHES WRN NOAM BY WED MODELS/ENSEMBLES SHOW
ONLY MODEST CONVERGENCE RELATIVE TO SPREAD FROM 24 HRS AGO...
STILL SHOWING A RANGE OF A RIDGE TO FLAT SHRTWV CROSSING THE NWRN
STATES.  IT TAKES NO MORE THAN ANOTHER DAY FOR THIS ISSUE TO
IMPACT THE AMPLITUDE/TIMING OF THE TROUGH CROSSING THE EAST. 
FURTHER COMPLICATING THE FCST IS UNCERTAINTY OVER PRECISE
EVOLUTION OF ENERGY AMPLIFYING INTO THE MIDWEST/GRTLKS FROM SWRN
CANADA DURING TUE-THU AND CONTINUING EWD THEREAFTER.

FOR DAYS 3-5 TUE-THU... MULTI-DAY TRENDS SEEM TO LEAN SOMEWHAT
AWAY FROM SOLNS LIKE THE 06Z GFS/GEFS MEAN THAT ARE MORE AMPLIFIED
WITH SHRTWV ENERGY REACHING THE NORTHWEST.  HOWEVER 24-HR TRENDS
OF THE 00Z MODELS/ENSEMBLE MEANS ONLY SUGGEST AN ATTEMPT TO
CONVERGE NEAR THE GUIDANCE AVG.  FARTHER EWD... THERE IS STILL A
FAIR AMOUNT OF SPREAD WITH THE SFC LOW LIKELY TRACKING INTO THE
GRTLKS REGION BY THU.  THE 00Z GFS/PARALLEL GFS AND GEFS
MEAN/ECMWF MEAN OFFER THE BEST INTERMEDIATE SOLN FOR THIS FEATURE.
 MEANWHILE THE COMBINATION OF UPSTREAM ISSUES MAY MAKE IT
DIFFICULT TO RESOLVE DETAILS OF WAVINESS OFF THE EAST
COAST/SUPPORTING MID LVL SHRTWV WED-THU UNTIL PERHAPS THE SHORT
RANGE TIME FRAME.  THE 00Z ECMWF IS ON THE WRN SIDE OF THE
MODEL/ENSEMBLE SPREAD BUT NOT QUITE TO THE POINT OF BEING AN
OUTLIER.  THE 00Z PARALLEL GFS IS ESSENTIALLY A STRONGER FORM OF
THE 00Z ECMWF MEAN AND THE 00Z GFS IS JUST SLIGHTLY EWD.  PREFER
THESE THREE SOLNS ALBEIT WITH ONLY MODEST CONFIDENCE.  THUS
OVERALL TUE-THU PREFS LEAN TO THE 00Z GFS/PARALLEL GFS/ECMWF MEAN
WITH THE 00Z ECMWF ACCEPTABLE AS A BLEND COMPONENT DAY 3 TUE.

BY DAYS 6-7 FRI-SAT ONE FOCUS WILL BE ON THE ERN PAC TROUGH/UPR
LOW WHICH WILL LIKELY COME UNDER SOME INFLUENCE OF UPSTREAM PAC
FLOW LATE IN THE PERIOD.  THE AMOUNT OF RIDGING AT HIGHER
LATITUDES ALONG WITH GEFS MEAN CONTINUITY/00Z ECMWF MEAN TREND
SUPPORT THE POTENTIAL FOR SOME UNDERCUTTING TROUGH ENERGY TO MOVE
INTO THE WEST.  THE 00Z GFS PARALLEL APPEARS TO BECOME MUCH TOO
AMPLIFIED WITH THIS TROUGH SO A SMALL COMPONENT OF THE OPERATIONAL
00Z GFS REPLACES THE PARALLEL RUN IN THE BLEND WITH THE 00Z
GEFS/ECMWF MEANS FOR THIS TIME FRAME.  FARTHER EWD THE ONE POINT
OF DISAGREEMENT AMONG THIS CLUSTER AND WITH THE MAJORITY OF OTHER
GUIDANCE IS THAT THE 00Z GFS IS SLOWER WITH SFC HIGH PRESSURE
BUILDING INTO THE CNTRL/ERN STATES.  THE FAVORED BLEND EMPHASIZES
THE NON-00Z GFS CONSENSUS WITH THIS ASPECT OF THE FCST.


...SENSIBLE WEATHER HIGHLIGHTS...

DURING THE FIRST HALF OF THE PERIOD THE MOIST FLOW ALONG A WAVY
FRONT NEAR/OFFSHORE THE EAST COAST WILL REQUIRE MONITORING... WITH
THE SMALLER SCALE OF IMPORTANT DETAILS LEADING TO BELOW AVG
PREDICTABILITY AT THIS TIME.  BEST POTENTIAL FOR HEAVIEST RNFL
SHOULD BE FROM NRN-CNTRL FL NEWD ALONG THE SERN/SRN MID ATLC
COAST.  GUIDANCE SPREAD PRESENTS A MORE DIFFICULT FCST FARTHER NWD
WITH SOLNS RANGING FROM A SUFFICIENTLY OFFSHORE WAVE TO KEEP THE
AREA DRY TO A STRONG/WWD WAVE THAT WOULD GENERATE SIGNIFICANT
INLAND SNOW/COASTAL RAIN.  CURRENT PREFS WOULD SUGGEST MORE PCPN
POTENTIAL THAN THE DRY SIDE OF THE SOLN ENVELOPE.  UPSTREAM ENERGY
AND ASSOC SFC LOW/COLD FRONT SHOULD BRING A MODEST AREA OF LGT
SNOW ACROSS NRN AREAS DURING THE WEEK.  PERIODS OF COLD CYCLONIC
FLOW WILL SUPPORT PERIODS OF LAKE EFFECT SNOW.  MOST CNTRL-ERN
CONUS TEMPS SHOULD BE BELOW NORMAL DURING THE PERIOD WITH GREATEST
ANOMALIES LIKELY SPREADING SEWD FROM THE NRN PLAINS THU-SAT.

EXTREME NRN PARTS OF THE WEST MAY SEE ENHANCED PCPN AT THE START
OF THE PERIOD TUE.  ERN PAC TROUGH/PSBL EMBEDDED UPR LOW SHOULD
BRING SOME INCREASE IN MSTR TO THE CNTRL-NRN WEST COAST BY
FRI-SAT.  DEPENDING ON THE EXACT EVOLUTION OF THIS FEATURE THERE
MAY BE SOME LOCALLY HEAVIER ACTIVITY.  WARMEST TEMPS VERSUS CLIMO
OVER THE WEST SHOULD BE FROM SRN OR THROUGH CA AND THE
GRTBASIN/SOUTHWEST AROUND WED-THU.  

RAUSCH