Preliminary Forecasts
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FXUS02 KWNH 270626
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 AM EDT SAT AUG 27 2016

VALID 12Z TUE AUG 30 2016 - 12Z SAT SEP 03 2016

...OVERVIEW...

BOTH THE MANUAL FCST AND GUIDANCE SPREAD FOR FEATURES OF INTEREST
HAVE REMAINED FAIRLY SIMILAR OVER THE PAST 12-24 HRS.  AGREEMENT
IS STILL GENERALLY BETTER THAN AVG WITH RESPECT TO LARGE SCALE
MEAN FLOW SETTLING INTO A TROUGH/RIDGE/TROUGH CONFIGURATION...
WITH THE WEST COAST TROUGH LIKELY TO BE SHARPER AND MORE AMPLIFIED
THAN THE TROUGH REACHING THE EAST COAST.  ON THE OTHER HAND THE
SOLN ENVELOPE IS AS WIDE AS EVER WITH THE ULTIMATE TRACK/EVOLUTION
OF THE WEAK FEATURE EXPECTED TO TRACK INTO THE GULF OF MEXICO FROM
NEAR THE CNTRL BAHAMAS.


...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT...

FOR THE FEATURE FCST TO REACH THE GULF OF MEXICO SOLNS RANGE FROM
THE 12Z CMC/CMC MEAN THAT TAKE A TRACK TO THE WRN HALF OF THE GULF
COAST TO ECMWF RUNS THAT HAVE LEANED TOWARD THE EXTREME ERN
GULF/FL PENINSULA.  WITH A HIGHER NUMBER OF GEFS/ECMWF ENSEMBLES
TENDING TO REMAIN OVER THE ERN HALF OF THE GULF AND CONFIDENCE IN
ANY ALTERNATIVE SCENARIO QUITE LOW... THE MANUAL FCST MAINTAINS
CONTINUITY WITH A WEAK SFC LOW TRACKING TO THE FL PANHANDLE.
FURTHER COMPLEXITIES IN THE FCST NEAR THE SERN COAST ARE PROVIDED
BY A WEAK FEATURE FCST TO RETROGRADE FROM JUST S OF BERMUDA AND
WEAK WAVINESS THAT IS SUGGESTED BY SOME GUIDANCE TO DEVELOP BY
MIDWEEK... WHETHER RELATED TO THE INITIAL BAHAMAS FEATURE OR
OTHERWISE.  CONSULT THE TROPICAL WEATHER OUTLOOK BY THE NATIONAL
HURRICANE CENTER FOR LATEST INFO ON TROPICAL FEATURES.

FOR THE MORE AGREEABLE MID-LATITUDE PATTERN THE FIRST
CONSIDERATION OF NOTE IS TO REMOVE THE 12Z ECMWF FROM THE FCST
AFTER DAY 5 THU AS IT BECOMES FASTER THAN CONSENSUS TO EJECT WEST
COAST TROUGH ENERGY INTO SRN CANADA AND AS A RESULT FLATTENS ERN
U.S. FLOW LATE IN THE PERIOD.  GFS RUNS FIT THE MEAN PATTERN
BETTER.  HOWEVER THE 12Z RUN TRACKS AN EMBEDDED UPR LOW SOMEWHAT
FARTHER SWD NEAR THE WEST COAST VS MOST OTHER SOLNS AND THE 18Z
GFS BECOMES MORE AMPLIFIED THAN CONSENSUS WITH THE SRN PART OF THE
TROUGH.  THE GFS IS ALSO LEANS A BIT TOWARD THE AMPLIFIED SIDE
WITH THE EAST COAST TROUGH.  ESPECIALLY BY DAYS 6-7 FRI-SAT THE
ENSEMBLE MEANS OFFER A GOOD INTERMEDIATE SOLN OVER THE EAST.  AT
THAT TIME FRAME EWD TRENDS OF THE GEFS MEAN TOWARD THE ECMWF MEAN
FOR THE WEST COAST TROUGH FAVOR MAINTAINING SOMEWHAT MORE ECMWF
MEAN WEIGHTING IN THE BLEND.

VARIOUS IDEAS FROM THE 12Z ECMWF/12Z-18Z GFS AND THEIR ENSEMBLE
MEANS ARE INCORPORATED INTO THE DAYS 3-4 TUE-WED FCST WITH DAY 5
BEGINNING TO REDUCE OPERATIONAL WEIGHT ON THE WAY TO A 60/40 BLEND
OF THE 12Z ECMWF MEAN/18Z GEFS MEAN FOR DAYS 6-7.


...WEATHER HIGHLIGHTS/THREATS...

LOCATIONS FROM THE GULF COAST THROUGH FLORIDA AND SOUTHEAST COAST
WILL NEED TO MONITOR POTENTIAL FOR AREAS OF HVY RNFL DEPENDING ON
HOW INDIVIDUAL FEATURES EVOLVE OVER THE GULF AND OFF THE SERN
COAST.  THE FCST OVER THIS AREA REMAINS VERY UNCERTAIN.  THE NWRN
U.S. SHOULD SEE PERIODS OF RNFL WITH THE AMPLIFIED UPR TROUGH NEAR
THE WEST COAST.  MONSOONAL MSTR MAY PROMOTE SOME SHWRS/TSTMS OVER
THE SRN ROCKIES WHILE SHRTWV ENERGY AND A NRN PLAINS FRONT COULD
GENERATE SOME LOCALLY HVY CONVECTION OVER/NEAR THE UPR MS VLY...
WITH SOME CNTRL PLAINS ACTIVITY PSBLY BRIDGING THE GAP BTWN THE
TWO AREAS.  EXPECT BELOW NORMAL HIGHS THROUGH THE PERIOD NEAR THE
WEST COAST UPR TROUGH.  FARTHER EWD IN THE WARM SECTOR THE
GRTBASIN/NRN ROCKIES AND ESPECIALLY NRN PLAINS WILL LIKELY SEE A
PERIOD OF WELL ABOVE NORMAL TEMPS... WITH THE LATTER SEEING PLUS
10F OR GREATER ANOMALIES INTO THU OR FRI.  ABOVE NORMAL TEMPS IN
THE EAST TO START THE PERIOD WILL TREND CLOSER TO NORMAL AS HIGH
PRESSURE BUILDS IN BEHIND A PASSING COLD FRONT.  SRN LATITUDES OF
THE EAST MAY REMAIN RATHER WARM THOUGH.

RAUSCH

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