Preliminary Forecasts
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FXUS02 KWNH 290642
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT FRI MAY 29 2015

VALID 12Z MON JUN 01 2015 - 12Z FRI JUN 05 2015

...OVERVIEW AND GUIDANCE EVALUATION...

MODEL AND ENSEMBLE GUIDANCE IS FAIRLY AGREEABLE IN DEPICTING MEAN
TROUGHING NEAR OR JUST INLAND FROM THE WEST COAST AND A BROADENING
MEAN RIDGE DOWNSTREAM.  EMBEDDED WITHIN THE MEAN RIDGE... AN UPR
LOW SHOULD MEANDER OVER THE LWR MS VLY/CNTRL GULF COAST REGION FOR
A MAJORITY OF THE PERIOD.  FLOW ALOFT SHOULD EXHIBIT A MODERATE
DEGREE OF PROGRESSION ACROSS SRN CANADA AND INTO THE EXTREME NRN
CONUS.

REVIEW OF LATEST AND RECENT SOLNS WOULD SUGGEST THE GREATEST
UNCERTAINTY WITHIN THE CONSENSUS LARGE SCALE PATTERN INVOLVES HOW
INDIVIDUAL SHRTWVS ENTER AND THEN EJECT FROM THE WEST COAST MEAN
TROUGH.  THE SCALE OF INDIVIDUAL IMPULSES IS SUFFICIENTLY SMALL TO
YIELD RELATIVELY LOW PREDICTABILITY.  THUS THE LOWEST CONFIDENCE
IS WITH ANY NRN TIER SFC WAVES WHOSE EVOLUTION WILL BE SENSITIVE
TO THESE IMPULSES ALOFT.  CONVECTIVE DEVELOPMENT MAY PLAY A ROLE
AS WELL.

ELSEWHERE... THERE IS ALSO SPREAD WITH SPECIFICS OF SRN CANADA/NRN
TIER CONUS FLOW DOWNSTREAM BUT WITH SOMEWHAT LESS RESULTING SPREAD
WITH THE SFC FRONT THAT IS EXPECTED TO REACH THE EXTREME NRN TIER.
 LIKEWISE DETAILS OF SHRTWV ENERGY CROSSING THE NORTHEAST DURING
THE FIRST HALF OF THE PERIOD MAY INFLUENCE THE EXACT SWD EXTENT OF
THE EAST COAST FRONT THAT SHOULD EXTEND BACK INTO THE LWR MS
VLY... WHERE THE WEAK UPR LOW MAY SUPPORT A SFC WAVE IN THE
MON-WED TIME FRAME.  POSN/DEPTH DIFFS WITH THE UPR LOW ARE FAIRLY
MODEST OVERALL.

THE ARRAY OF GUIDANCE AND CONTINUITY SUGGEST THAT AN INTERMEDIATE
SOLN SHOULD WORK WELL OVER MOST AREAS.  PREFER TO MAINTAIN GREATER
EMPHASIS ON THE 18Z GEFS/12Z ECMWF MEANS IN LIGHT OF THE BETTER
CLUSTERING IN THE MEAN PATTERN THAN THE DETAILS BUT THE 12Z
GFS/ECMWF RUNS ARE CLOSE ENOUGH OVER MOST AREAS TO MERIT MINORITY
INCLUSION IN THE BLEND FOR MOST OF THE PERIOD.


...SENSIBLE WEATHER HIGHLIGHTS/THREATS...

EXPECT MOST OF THE SRN PLAINS TO SEE A PERIOD OF DRIER WEATHER
THAN IN RECENT WEEKS.  ONE AREA OF ORGANIZED RNFL/CONVECTION
SHOULD EXTEND FROM THE NRN ROCKIES ACROSS THE NRN PLAINS AND
VICINITY IN ASSOC WITH ONE OR MORE SFC WAVES AND A FRONT DRIFTING
NEAR/INTO THE EXTREME NRN TIER FROM CANADA.  THE OTHER FAVORED
AREA FOR HIGHER RNFL TOTALS IS OVER THE SERN THIRD OF THE CONUS
WITH A MID ATLC TO LWR MS VLY SFC FRONT AND WEAK UPR LOW OVER THE
LWR MS VLY/CNTRL GULF COAST AIDING ACTIVITY.  SRN/ERN PARTS OF THE
FL PENINSULA MAY ALSO SEE A PERIOD OF ENHANCED RNFL NEAR AN
INVERTED SFC TROUGH SUGGESTED BY SOME GUIDANCE.  THE PREFERRED
BLEND DOWNPLAYED THE STRENGTH OF 12Z/18Z GFS RUNS THOUGH AND
INDEED THE NEW 00Z GFS HAS ADJUSTED WEAKER THROUGH 12Z NEXT FRI.
WARMEST ANOMALIES FOR TEMPS SHOULD PROGRESS FROM THE NRN HIGH
PLAINS EARLY NEXT WEEK INTO THE NORTHEAST BY LATE IN THE WEEK.  ON
THE OTHER HAND ONSHORE FLOW ALONG THE EAST COAST SHOULD BRING 2-3
DAYS OF BELOW NORMAL MAX TEMPS THAT WILL FEEL QUITE COOL GIVEN
PRECEDING WARMTH.

RAUSCH

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