Preliminary Forecasts
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FXUS02 KWNH 170644
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT THU APR 17 2014

VALID 12Z SUN APR 20 2014 - 12Z THU APR 24 2014

...OVERVIEW AND PREFERENCES...

GUIDANCE CONTINUES TO EXHIBIT SOME DEGREE OF ADJUSTMENT/SHUFFLING
WITH VARIOUS MEDIUM TO SMALLER SCALE SHRTWV DETAILS OVER THE
CNTRL-ERN CONUS INTO THE ATLC FROM THE WEEKEND INTO EARLY NEXT
WEEK.  HOWEVER THE FCST IS ON TRACK FOR INCREASED DOMINANCE OF
LARGER SCALE FEATURES BY THE LATTER HALF OF THE PERIOD... WHICH
SHOULD INCREASE PREDICTABILITY OF PRIMARY SYSTEMS EVEN IF SOME
EMBEDDED DETAILS STILL HAVE LOWER CONFIDENCE.  FOR THE OVERALL
FCST PERIOD PREFER TO LEAN PRIMARILY TOWARD THE PAST TWO ECMWF
RUNS AND 12Z ECMWF MEAN GIVEN ESTABLISHED CONTINUITY FOR THE
AMPLIFYING ERN PAC TROUGH MOVING THROUGH THE WEST TOWARD THE
PLAINS TUE-THU AND SYSTEM OFF THE SERN COAST EARLIER IN THE
PERIOD... WITH GFS/GEFS SOLNS STILL IN THE PROCESS OF TRENDING
TOWARD THE PREFERRED SCENARIO.  NRN TIER EVOLUTION BETWEEN THESE
TWO SYSTEMS REMAINS SOMEWHAT MORE VARIABLE.


...GUIDANCE EVALUATION...

SOLNS SINCE THE 12Z CYCLE ARE SHOWING LESS SPREAD THAN PRIOR RUNS
FOR THE AMPLIFYING ERN PAC TROUGH MOVING THROUGH THE WEST TUE-WED
AND NEARING OR REACHING THE PLAINS BY THU.  THE EXACT EVOLUTION OF
THIS TROUGH WILL DEPEND ON DETAILS OF MULTIPLE PIECES OF ENERGY
ORIGINATING FROM THE NRN PAC/ALEUTIANS AS WELL AS A NERN PAC
CLOSED LOW... SO IT WILL TAKE SOME TIME TO RESOLVE DETAILS SUCH AS
THE TRACK OF A PSBL EMBEDDED CLOSED LOW AS THE TROUGH CROSSES THE
WEST.  SOME EARLIER GFS/GEFS RUNS HAD TRACKED AN UPR LOW RATHER
FAR SWD BUT GENERALLY APPEAR TO BE TRENDING TOWARD ECMWF/ECMWF
MEAN SOLNS.  THE 12Z CMC MEAN STILL IMPLIED AN UPR LOW TRACK
ACROSS THE GRTBASIN THOUGH.  ONCE THE SYSTEM EMERGES INTO THE
PLAINS THE 12Z ECMWF MAY BECOME A LITTLE FAST/FLAT DUE TO LESS
AMPLIFIED UPSTREAM FLOW RELATIVE TO OTHER SOLNS... MERITING SOME
INCLUSION OF THE OLD 00Z ECMWF RUN AS WELL TO ADD SOME OPERATIONAL
DETAIL TO THE 12Z ECMWF MEAN.  AMPLIFIED NATURE OF THE PATTERN
COULD ALSO SUPPORT A SMALL MINORITY COMPONENT OF THE MORE
AMPLIFIED 18Z GEFS MEAN.  BY DAYS 6-7 WED-THU THERE IS BETTER THAN
AVERAGE ENSEMBLE CLUSTERING TOWARD THE IDEA OF A SIGNIFICANT SFC
SYSTEM REACHING THE NRN HALF OF THE PLAINS.

BY MIDWEEK THE DOWNSTREAM RESPONSE TO THE WRN TROUGH WILL BE A
CNTRL CONUS RIDGE AND EAST COAST/WRN ATLC TROUGH.  THERE IS NOW
GOOD AGREEMENT WITH THE TIMING/AMPLITUDE OF THE EAST COAST TROUGH
AS OF DAY 6 WED ASIDE FROM THE 18Z GFS THAT LIKELY BECOMES TOO
SHARP/AMPLIFIED.  THIS TROUGH SHOULD LEAD TO CONSOLIDATION OF SFC
LOW PRESSURE OFF THE NERN COAST/CANADIAN MARITIMES.

BEFORE THIS TROUGH DEVELOPS THERE WILL BE A COUPLE WEAK SFC
SYSTEMS ASSOC WITH A COUPLE SHRTWVS ALONG THE US-CANADIAN BORDER.
CONSENSUS IS SOMEWHAT SLOWER THAN PRIOR CONTINUITY ESPECIALLY WITH
A LEADING FRONT CROSSING THE GRTLKS EARLY IN THE PERIOD.  AT THE
SAME TIME SHRTWV ENERGY EJECTING FROM THE SRN ROCKIES/PLAINS MAY
ALSO SUPPORT A WEAK SFC REFLECTION.

WITH THE SYSTEM OFF THE SERN COAST... THERE ARE STILL SOME
UNRESOLVED SHORT RANGE ISSUES THAT TEMPER CONFIDENCE IN THE MEDIUM
RANGE.  LATEST GFS/GEFS RUNS HAVE FINALLY TRENDED CLOSER TO
REMAINING GUIDANCE BUT STILL POSE SOME QUESTION MARKS... WHILE
UKMET/CMC RUNS REMAIN ON THE NWRN SIDE OF THE SPREAD.  AN AVG OF
RECENT ECMWF RUNS PROVIDES THE BEST INTERMEDIATE AND STABLE SOLN
WITH GOOD SUPPORT IN PRINCIPLE FROM THE 12Z ECMWF MEAN.


...SENSIBLE WEATHER HIGHLIGHTS...

A LEADING SYSTEM WILL BRING SOME PCPN TO THE PAC NW EARLY IN THE
PERIOD AND THEN MSTR ASSOC WITH THE VIGOROUS ERN PAC TROUGH
EVENTUALLY CROSSING THE WEST SHOULD SPREAD RNFL AND HIGHER ELEV
SNOW ACROSS APPROX THE NRN HALF OF THE REGION DURING THE FIRST
HALF OF NEXT WEEK WITH RNFL ALSO EXTENDING ACROSS THE NRN
PLAINS/UPR MS VLY TUE-WED.  CURRENTLY EXPECT ENOUGH SFC
DEVELOPMENT TO PROMOTE FAIRLY STRONG WINDS AT SOME LOCATIONS FROM
THE WEST INTO THE PLAINS DURING THE TUE-THU TIME FRAME.
PROGRESSION OF THIS SYSTEM WILL LEAD TO A SIGNIFICANT COOLING
TREND FROM INITIALLY ABOVE NORMAL TEMPS OVER THE WEST... AND BY
TUE-WED PROMOTE VERY WARM TEMPS OVER THE PLAINS WITH SOME HIGHS
REACHING 15-20F ABOVE NORMAL.

A COMBINATION OF NRN AND SRN STREAM FEATURES WILL SUPPORT A BAND
OF RNFL PROGRESSING EWD FROM THE PLAINS/GRTLKS SUN ONWARD WITH
HEAVIER ACTIVITY PSBL IN SOME LOCATIONS BUT NOT LIKELY ON A
WIDESPREAD SCALE DUE TO LACK OF PRONOUNCED GULF INFLOW.  PCPN MAY
BE SLOWER TO DEPART FROM NEW ENGLAND DUE TO THE SYSTEM FCST TO
DEVELOP OFF THE NERN COAST BY MIDWEEK.  EARLY IN THE PERIOD AREAS
ALONG THE SERN COAST MAY SEE LINGERING CLOUDS/RNFL FROM THE WAVE
OFFSHORE.  ERN CONUS TEMPS SHOULD BE VARIABLE BUT WITHIN 10F OF
NORMAL MOST DAYS.

RAUSCH

$$





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