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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0628Z Apr 14, 2014)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 AM EDT MON APR 14 2014

VALID 12Z THU APR 17 2014 - 12Z MON APR 21 2014

...OVERVIEW AND PREFERENCES...

DURING THE MEDIUM RANGE PERIOD THE MAJORITY OF GUIDANCE IS SHOWING
AN EVOLUTION TOWARD AN ERN PAC TROUGH/WRN NOAM RIDGE/ERN NOAM
TROUGH CONFIGURATION BUT WITH A LOT OF SPREAD IN THE DETAILS. 
SOME OF THE UNCERTAINTY WITH NRN STREAM FLOW WILL ALSO LIKELY
IMPACT THE PROGRESSION OF A SRN STREAM ERN PAC TROUGH/UPR LOW
HEADING INTO THE SWRN CONUS/NWRN MEXICO BY NEXT FRI-SAT. 
OPERATIONAL MODEL SOLNS DEVELOP SOME MEANINGFUL DETAIL DIFFS
ALREADY AS OF THE START OF THE FCST WITH FURTHER DIVERGENCE
THEREAFTER.  THUS PREFER TO MAINTAIN AN ENSEMBLE MEAN APPROACH
INCORPORATING HALF OF THE 12Z ECMWF MEAN AND THE REMAINDER 12Z
GEFS/NAEFS MEANS.  MODEST DETAIL ENHANCEMENTS WERE MADE TO THIS
INITIAL BLEND WHERE APPROPRIATE.


...GUIDANCE EVALUATION...

AS HAS BEEN THE CASE OVER RECENT DAYS... MODELS ARE STILL
UNDECIDED OVER EXACTLY HOW TO DEPICT ENERGY NEAR THE CNTRL
US-CANADIAN BORDER AS OF DAY 3 THU AND HOW MUCH INTERACTION THERE
WILL BE BETWEEN THIS ENERGY AND A VIGOROUS SHRTWV INITIALLY OVER
THE CNTRL-SRN ROCKIES/PLAINS.  THE MOST AGREEABLE THEME AMONG ALL
MODEL/ENSEMBLE SOLNS HAS BEEN TOWARD SOME DEGREE OF SFC
DEVELOPMENT FROM THE MID MS VLY INTO THE GRTLKS AROUND DAYS 4-5
FRI-SAT BUT PERHAPS NOT WITH THE STRENGTH OF SOME RECENT GFS/CMC
RUNS.  AT THE START OF THE FCST THE 12Z ECMWF COMPARES LEAST
FAVORABLY TO OTHER SOLNS NEAR THE CANADIAN BORDER AS IT HOLDS MID
LVL ENERGY FARTHER NWWD.  BY FRI-SAT RECENT ECMWF/UKMET RUNS HAVE
BEEN KEEPING SRN ENERGY MORE DETACHED ALLOWING FOR MORE EMPHASIS
OF A COASTAL SFC WAVE.  IN SPITE OF THE INDIVIDUAL MODEL/ENSEMBLE
SPREAD FOR SFC DETAILS OVER THE EAST... THERE HAS BEEN A DECENT
SIGNAL FROM THE MEANS TOWARD A CONSOLIDATION OF LOW PRESSURE
OVER/NEAR THE NORTHEAST BY SUN WHICH IS QUITE PLAUSIBLE IN LIGHT
OF THE MEAN TROUGH POSN AT THAT TIME.  

AN ADDED COMPLICATION TO ERN CONUS EVOLUTION IS THE PSBL INFLUENCE
FROM ERN PAC SHRTWV ENERGY THAT SHOULD BE COMING ASHORE BY THU
NIGHT-FRI AND BEGINNING TO FEED INTO THE ERN MEAN TROUGH BY THE
LATTER HALF OF THE FCST.  THE 12Z ECMWF HAS ONE OF THE DEEPER/MORE
CONCENTRATED DEPICTIONS OF THIS PAC SHRTWV EARLIER IN THE PERIOD
WHILE THE 12Z/18Z GFS RUNS BECOME MORE AMPLIFIED THAN CONSENSUS
OVER THE EAST BY NEXT SUN-MON.  THE NEW 00Z GFS HAS TONED DOWN THE
DEPTH OF THIS SHRTWV.

FARTHER WWD THE 12Z/18Z GFS RUNS ARE SOMEWHAT ON THE AGGRESSIVE
SIDE OF THE SPREAD WITH HGT FALLS REACHING THE WEST COAST BY DAY 7
MON.  THE 00Z GFS APPEARS TO BE MORE IN LINE WITH THE ENSEMBLE
MEANS.  THE 18Z GEFS MEAN IS LESS AMPLIFIED THAN A MAJORITY THOUGH
NOT ALL OF OTHER SOLNS WITH THE ERN PAC TROUGH/WRN CONUS RIDGE...
HENCE THE INCLUSION OF THE 12Z GEFS MEAN IN THE FAVORED BLEND.

THERE IS STILL A MODERATE DEGREE OF SPREAD WITH THE SRN STREAM ERN
PAC TROUGH/UPR LOW HEADING INTO THE SWRN STATES/NWRN MEXICO.  GFS
RUNS HAVE TENDED TO BE ON THE FASTER SIDE OF THE TIMING SPREAD BUT
A SLIGHTLY SLOWER TREND IN THE NEW 00Z RUN HAS REDUCED THE SPREAD
SOMEWHAT.  IN ADDITION THE 12Z ECMWF/ECMWF MEAN HINT AT SOME
ENERGY PSBLY EJECTING FROM THE FEATURE IN A MANNER SIMILAR TO THE
00Z GFS.  TIMING WILL BE SENSITIVE TO EXACTLY WHEN THE NWRN CONUS
SHRTWV PASSES BY AND RIDGING BUILDS INTO THE INTERIOR WEST.


...SENSIBLE WEATHER HIGHLIGHTS...

PROGRESSIVE SHRTWV COMING ASHORE OVER THE NW LATE THIS WEEK WILL
BRING A BRIEF PERIOD OF PCPN TO THE PAC NW/NRN ROCKIES.  THEN THE
ESTABLISHMENT OF THE ERN PAC TROUGH ALOFT SHOULD BRING SOME MSTR
INTO AT LEAST THE NRN PAC NW AND PSBLY EXTREME NRN ROCKIES ALBEIT
WITH FAIRLY MODEST TOTALS.  WRN CONUS TEMPS SHOULD BE NEAR TO
ABOVE NORMAL WITH HIGHS UP TO 10-15F ABOVE NORMAL ON SOME DAYS
OVER CNTRL-SRN AREAS.  LOWER LATITUDE ERN PAC FEATURE ALOFT MAY
SUPPORT SOME PCPN OVER THE FOUR CORNERS SRN ROCKIES BY SAT WITH
SOME ACTIVITY EXTENDING INTO THE PLAINS THEREAFTER.

LATE THIS WEEK THE ERN 2/3 OF THE LOWER 48 WILL SEE BELOW TO MUCH
BELOW NORMAL TEMPS HIGHLIGHTED BY AN AREA OF MINUS 15-25F
ANOMALIES FOR DAYTIME HIGHS FROM THE ERN SLOPES OF THE ROCKIES
INTO THE CNTRL PLAINS ON THU.  SOME PCPN MAY BE IN THE FORM OF
SNOW FROM THE ROCKIES INTO THE UPR GRTLKS... WITH UPR MS
VLY/GRTLKS PCPN TYPE DEPENDING ON STRENGTH OF MID MS VLY INTO
GRTLKS DEVELOPMENT FRI-SAT.  WITH TIME A BROAD AREA OF MSTR SHOULD
SPREAD E/NE FROM THE PLAINS THROUGH THE EAST COAST AND TEMPS
SHOULD MODERATE TOWARD NORMAL.  UNCERTAINTY WITH SPECIFICS OF HOW
THE ERN CONUS SYSTEM/S WILL EVOLVE LEADS TO FAIRLY LOW CONFIDENCE
IN PINPOINTING WHERE HEAVIEST RNFL MAY OCCUR WITH THE GULF
COAST/SOUTHEAST CURRENTLY SEEING SLIGHTLY HIGHER POTENTIAL THAN
ELSEWHERE.

RAUSCH