Preliminary Forecasts
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FXUS02 KWNH 160638
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 AM EDT WED APR 16 2014

VALID 12Z SAT APR 19 2014 - 12Z WED APR 23 2014

...OVERVIEW AND PREFERENCES...

THROUGH THE WEEKEND INTO THE BEGINNING OF NEXT WEEK MODELS AND
ENSEMBLES HAVE BEEN DISPLAYING SOME DIFFICULTY IN RESOLVING THE
DETAILS OF MEDIUM TO SMALLER SCALE FEATURES CONTAINED IN NRN AND
SRN STREAM FLOW AS WELL AS PSBL STREAM INTERACTIONS... LEADING TO
LESS THAN IDEAL AGREEMENT/CONTINUITY IN RECENT DAYS.  BY LATER IN
THE FCST A TREND TOWARD LARGER SCALE FEATURES... NAMELY A WRN
TROUGH/PLAINS RIDGE/EAST COAST TROUGH... WILL HOPEFULLY IMPROVE
PREDICTABILITY.  FOR THE DAYS 3-5 SAT-MON PERIOD A SOLN CONSISTING
OF HALF 12Z ECMWF MEAN AND THE REMAINDER 12Z ECMWF/18Z GFS
PROVIDES THE BEST INTERMEDIATE STARTING POINT FOR SYSTEMS OF
INTEREST.  BY DAYS 6-7 TUE-WED PREFER A 70/30 BLEND OF THE 12Z
ECMWF MEAN/18Z GEFS MEAN FOR HANDLING THE ARRIVAL OF THE WRN
TROUGH AND AMPLITUDE OF THE EAST COAST TROUGH.


...GUIDANCE EVALUATION...

AS OF THE START OF THE PERIOD EARLY SAT THERE ARE STILL
SIGNIFICANT DIFFS WITH THE AMPLITUDE/TIMING OF A DEPARTING ERN
CONUS TROUGH.  GFS/GEFS SOLNS ARE ON THE SLOWER/MORE AMPLIFIED
SIDE OF THE FULL SPREAD WITH THE NRN PART OF THE TROUGH AND
FAST/OPEN WITH SRN ENERGY WHICH ECMWF/UKMET/CMC RUNS CLOSE OFF
WITH MUCH SLOWER TIMING AND SUPPORT A WAVE NEAR/OFFSHORE THE SERN
COAST.  MODEL/ENSEMBLE MEAN TRENDS OVER THE PAST 1-2 DAYS HAVE
BEEN TOWARD A FASTER/FLATTER NRN STREAM TROUGH WHICH WOULD OPEN
THE DOOR TO MORE SEPARATION OF THE SRN ENERGY.  THERE ARE STILL
MULTIPLE UNCERTAINTIES WITH EXACTLY HOW THE SRN FEATURE WILL
EVOLVE LEADING INTO THE MEDR PERIOD... LOWERING CONFIDENCE IN A
PARTICULAR OPERATIONAL MODEL SOLN... BUT THE 18Z GEFS MEAN FAVORS
SRN TROUGH TIMING CLOSE TO THE 12Z ECMWF MEAN SO THERE IS AT LEAST
REASONABLE CONFIDENCE IN SLOWER TIMING THAN GFS RUNS.  THE NEW 00Z
UKMET/CMC SHOW TIMING EVEN SLOWER THAN THE 12Z ECMWF.

SOME INTERACTION IS ALSO PSBL AMONG A SHRTWV INITIALLY OVER THE
NRN ROCKIES/PLAINS AND SRN STREAM TROUGH REACHING THE SW BY SAT.
THIS OVERALL AREA OF ENERGY IS FCST TO PROGRESS EWD AS A MODEST
SHRTWV SUPPORTING A FAIRLY WEAK SFC SYSTEM THAT MAY BECOME BETTER
DEFINED ONCE UPSTREAM ENERGY REACHES THE NORTHEAST BY LATE IN THE
FCST.  THERE HAS BEEN A NOTICEABLY FASTER CONSENSUS TREND WITH THE
SRN ENERGY.  AMPLITUDE OF THE WRN-CNTRL CONUS PATTERN BY MIDWEEK
APPEARS MORE SUPPORTIVE OF THE 12Z ECMWF MEAN/18Z GEFS MEAN THAT
ARE MORE AMPLIFIED WITH THE EAST COAST TROUGH THAN THE 12Z CMC/CMC
MEAN AND NEW 00Z GFS.

GFS/GEFS RUNS CONTINUE TO SHOW FASTER PROGRESSION THAN MOST OTHER
SOLNS WITH A WRN PAC SYSTEM LEADING TO EARLIER ARRIVAL OF THE
TROUGH NEAR THE WEST COAST.  THE CASE FOR A SLOWER TROUGH IS NOT
QUITE AS CONVINCING TODAY THOUGH... AS THE 12Z CMC MEAN IS AS FAST
AS THE GEFS MEAN AND THE NEW 00Z CMC IS EVEN FASTER THAN THE GFS
WITH BOTH WRN AND ERN PAC TROUGHS.  A 70/30 WEIGHTING OF THE 12Z
ECMWF MEAN/18Z GEFS MEAN SEEMS TO PROVIDE THE BEST BALANCE OF
CONTINUITY AND PARTIAL ACCOUNT FOR THE POSSIBILITY OF SLIGHTLY
FASTER TIMING THAN THE ECMWF/ECMWF MEAN.  ALSO NOTED IS THE GFS
TENDENCY TO CLOSE OFF AN EMBEDDED UPR LOW OVER THE SW OR GRTBASIN.
 THIS IS WITHIN THE GEFS SPREAD BUT EXTREME RELATIVE TO ECMWF/CMC
ENSEMBLE MEMBERS.  GFS/GEFS SOLNS HAVE HAD RECENT ISSUES WITH
BEING TOO AGGRESSIVE TO AMPLIFY/CLOSE OFF ENERGY CROSSING THE WEST
BUT THE AMPLIFIED NATURE OF THE OVERALL PATTERN LEAVES SOME MODEST
POTENTIAL FOR A GFS SCENARIO.


...SENSIBLE WEATHER HIGHLIGHTS...

SYSTEM CROSSING THE NORTHEAST DURING THE WEEKEND WILL LIKELY
GENERATE AREAS OF MOSTLY LGT PCPN PSBLY INCLUDING SOME POCKETS OF
SNOW IN NRN AREAS.  AT THE SAME TIME THE SERN COAST MAY SEE
LINGERING CLOUDS/RNFL DUE TO A SLOW MOVING/CLOSED MID LVL SYSTEM
AND ASSOC SFC WAVE.  UPSTREAM THE COMBINATION OF A NRN STREAM
PLAINS SHRTWV AND ENERGY EJECTING FROM THE SW WILL SUPPORT AN AREA
OF RNFL SPREADING EWD/NEWD FROM THE FOUR CORNERS/SRN HIGH PLAINS
AND NERN PLAINS/UPR MS VLY.  SOME ACTIVITY MAY BE LOCALLY HVY.
EXCEPT FOR NRN AREAS MOST OF THE WEST SHOULD SEE WARM TEMPS
SAT-MON WITH SOME 10-15F ABOVE NORMAL HIGHS.  AS THE AMPLIFYING
ERN PAC TROUGH ARRIVES IN THE WEST NEXT WEEK EXPECT A COOLING
TREND WHILE THE WARMTH HEADS INTO THE PLAINS... WHILE AREAS FROM
THE NRN HALF OF THE WEST COAST INTO THE NRN PLAINS SHOULD SEE
INCREASED COVERAGE OF PCPN.  MSTR COULD EXTEND FARTHER SWD OVER
THE WEST IF THE TROUGH ALOFT ENDS UP BEING DEEPER/MORE CLOSED LIKE
SOME GFS RUNS.

RAUSCH

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