Preliminary Forecasts
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000
FXUS02 KWNH 010651
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 AM EDT MON JUN 01 2015

VALID 12Z THU JUN 04 2015 - 12Z MON JUN 08 2015

...PATTERN OVERVIEW...

CONUS FLOW SHOULD BE RATHER AMPLIFIED DURING THE PERIOD.  THE MOST
PROMINENT FEATURES WILL BE A DEEP TROUGH AND EMBEDDED CLOSED LOW
EVOLVING NEAR/JUST INLAND FROM THE WEST COAST... AND A STRONG
RIDGE ANCHORED OVER THE SRN PLAINS/NRN MEXICO.  MEANWHILE ERN
CONUS TROUGHING SHOULD CONSIST OF INITIAL ENERGY PSBLY FOLLOWED BY
WEAKER ENERGY ROUNDING THE PLAINS RIDGE.  AT HIGHER LATITUDES AN
ERN CANADA TROUGH SHOULD BRUSH THE NORTHEAST MID-PERIOD WHILE WRN
CANADA ENERGY MAY BEGIN TO DROP INTO THE NRN TIER AS WRN CANADA
RIDGING STRENGTHENS.  WITH D+8 MULTI-DAY MEANS AGREEING UPON A
CORE OF POSITIVE HGT ANOMALIES OVER SWRN CANADA AT THAT TIME...
TELECONNECTIONS SUGGEST THAT ERN CONUS FLOW SHOULD EVENTUALLY
EVOLVE TOWARD MODERATE TO AMPLIFIED TROUGHING.


...GUIDANCE EVALUATION...

GUIDANCE SUGGESTS INCREASING CONFIDENCE IN FORMATION OF A CLOSED
LOW ALOFT OVER OR NEAR CA LATE THIS WEEK WITH FAIRLY SLOW
PROGRESSION THEREAFTER AS MIGHT BE EXPECTED GIVEN THE RIDGE FCST
TO BUILD OVER THE PAC NW/SRN BC.  FOR PART OF THE PERIOD THE NEW
00Z GFS TRACKS THE UPR LOW FARTHER OFFSHORE THAN THE MAJORITY OF
OTHER SOLNS WHILE THE UKMET/CMC ARE A LITTLE MORE PROGRESSIVE.
THIS LEAVES THE 12Z ECMWF/ECMWF MEAN AND 18Z GEFS/12Z NAEFS MEAN
AS THE BEST MAJORITY/INTERMEDIATE SOLN.  AN ONGOING CONCERN IS THE
EXTENT TO WHICH THE TROUGH INTERACTS WITH MSTR/ENERGY ALOFT ASSOC
WITH WEAKENING EPAC TROPICAL CYCLONE ANDRES.  GFS RUNS CONTINUE TO
BE ON THE EXTREME ERN SIDE OF THE GUIDANCE SPREAD FOR SFC LOW
TRACK OF ANDRES AND AGGRESSIVE WITH HOW MUCH MSTR IS PULLED INTO
THE WRN STATES.  HOWEVER EVEN THE PAST COUPLE UKMET RUNS AND 12Z
ECMWF TO SOME DEGREE PULL UP SOME MID LVL ENERGY/MSTR INTO THE WRN
CONUS.

MODELS/ENSEMBLES CONTINUE TO HAVE DIFFICULTY HOLDING ONTO AN
AGREEABLE AND/OR CONSISTENT SOLN FOR ERN CONUS EVOLUTION.
CONTINUING THE PRECEDENT OF ALTERNATING TRENDS FOR THE TROUGH
INITIALLY OVER THE EAST... 12Z/18Z AND NEW 00Z RUNS ARE SOMEWHAT
MORE OPEN/EWD THAN YDAYS SLOWER/CLOSED SOLNS.  EARLY ON THE
12Z/18Z GFS RUNS WERE A LITTLE SW OF OTHER SOLNS WITH THE POSN OF
THE EMBEDDED UPR LOW.  LITTLE HAS CHANGED WITH THE RELATIVE
DISTRIBUTION OF GUIDANCE AHEAD OF THIS FEATURE AS GFS/GEFS/CMC
SOLNS CONTINUE TO BE STRONGEST WITH WRN ATLC LOW PRES.
PROGRESSIVE SSWLY FLOW ALOFT AHEAD OF THE TROUGH DOES NOT SEEM TO
BE TOO FAVORABLE FOR SFC DEVELOPMENT OF A TROPICAL NATURE... WITH
WAVINESS MORE LIKELY TO BE CONNECTED TO ENERGY ALOFT.  IT WILL
STILL TAKE TIME TO RESOLVE IMPORTANT SUBTLE DETAILS WITH
INDICATIONS THAT INITIAL ERN ENERGY MAY BE EJECTED AS ONE OR MORE
UPSTREAM IMPULSES FEED INTO THE MEAN TROUGH.  FARTHER NWD THE
CONSENSUS OF GUIDANCE IS CURRENTLY HEADING TOWARD GREATER
SUPPRESSION OF A NRN INTO ERN CONUS COLD FRONT AS HIGH PRES TRACKS
FROM CNTRL INTO ERN CANADA.  THERE IS STILL ENOUGH SPREAD AND DAY
TO DAY INSTABILITY TO BE WARY OF ADJUSTING TO LATEST GFS/ECMWF
RUNS QUITE YET.

THE LAST FCST ISSUE OF NOTE EMERGES OVER THE NRN TIER TOWARD THE
END OF THE PERIOD AS LATE WEEK WRN CANADA ENERGY BEGINS TO TRACK
DOWNSTREAM FROM THE BUILDING WRN CANADA RIDGE.  SOME OPERATIONAL
GFS/ECMWF RUNS ARE SHOW A FAIRLY STRONG SFC LOW REACHING ONTARIO
BY DAY 7 MON WITH A COLD FRONT EXTENDING INTO THE CONUS.  THUS FAR
ENSEMBLES ARE LESS DEFINED WITH THIS SYSTEM.

IN ORDER TO LEAN AWAY FROM THE LESS CONFIDENT ASPECTS OF GFS/GEFS
SOLNS AND THEN EMPHASIZE ENSEMBLE GUIDANCE GIVEN TYPICALLY
DECREASING CONFIDENCE IN OPERATIONAL MODELS WITH TIME... THE
UPDATED PREFERENCE STARTS WITH A BLEND OF THE 12Z ECMWF/ECMWF
MEAN/NAEFS MEAN DAYS 3-4 THU-FRI AND A 70/30 BLEND OF THE ECMWF
MEAN/NAEFS MEAN THEREAFTER.


...SENSIBLE WEATHER HIGHLIGHTS/THREATS...

UPR SYSTEM EVOLVING OVER THE WEST WILL SUPPORT UNSETTLED WEATHER
OVER SOME AREAS WITH THE EXTENT/LOCATION OF LOCALLY HEAVIER AMTS
DETERMINED IN PART BY HOW MUCH IF ANY MSTR FROM ANDRES IS PULLED
INTO THE REGION.  THE GREATEST UNCERTAINTY IN THIS REGARD LIES
OVER THE SWRN STATES AND FOUR CORNERS REGION WHILE THERE IS BETTER
CONSENSUS TOWARD A FAVORED AXIS OF RNFL FROM NRN-CNTRL CA INTO THE
NRN ROCKIES.  FARTHER EWD... POTENTIAL EXISTS FOR EPISODES OF
LOCALLY HVY CONVECTION FROM THE NRN-CNTRL HIGH PLAINS INTO THE MS
VLY.  THIS ACTIVITY WILL BE SUPPORTED BY A COMBINATION OF BUNDLES
OF SHRTWV ENERGY EJECTING FROM THE WEST ALONG WITH A PERSISTENT
PLAINS SFC FRONT AND LOW LVL UPSLOPE FLOW OVER THE HIGH PLAINS.
CONSULT SPC OUTLOOKS FOR LATEST INFO REGARDING SEVERE THREATS
WITHIN THIS AREA.  UPR TROUGHING OVER THE EAST AND EVENTUALLY AN
APPROACHING COLD FRONT SHOULD SUPPORT HIGHEST ERN CONUS RNFL
TOTALS OVER PORTIONS OF THE CNTRL-SRN APLCHNS AND MID
ATLC/SOUTHEAST.  MOIST SSWLY FLOW FROM THE WRN CARIBBEAN MAY ALSO
PROMOTE ENHANCED RNFL OVER SRN FL.  AS SUPPORTED BY
TELECONNECTIONS... THE RIDGE ALOFT BUILDING NEAR THE WRN
US-CANADIAN BORDER SHOULD SUPPORT WELL ABOVE NORMAL TEMPS OVER THE
NWRN STATES WITH PLUS 10-20F ANOMALIES FOR HIGHS AFTER THU AND
ESPECIALLY SAT-MON.  AREAL COVERAGE OF EITHER WARM OR COOL DOUBLE
DIGIT ANOMALIES SHOULD BE FAIRLY LIMITED ELSEWHERE DURING THE
PERIOD... WITH A TENDENCY TOWARD MODERATELY ABOVE NORMAL LOWS AND
BELOW NORMAL HIGHS.

RAUSCH

$$





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