Prognostic Meteorological Discussion
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FXUS02 KWBC 291558
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT SAT AUG 29 2015

VALID 12Z TUE SEP 01 2015 - 12Z SAT SEP 05 2015

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

LATEST GUIDANCE SHOWS A RELATIVELY SLOW EVOLUTION OF THE LARGE
SCALE PATTERN FEATURING AN AMPLIFIED UPR TROUGH NEAR/INLAND FROM
THE WEST COAST... DOWNSTREAM RIDGING... AND AN EXTREME ERN CANADA
TROUGH WHOSE INFLUENCE MAY EXTEND INTO NEW ENGLAND AT TIMES.

FOR MOST OF THE PERIOD THERE IS REASONABLE CONSENSUS AMONG THE 06Z
GFS/GEFS MEAN AND 00Z ECMWF/ECMWF MEAN FOR DETAILS OF THE WRN
TROUGH ALONG WITH THE DOWNSTREAM RIDGE AND ERN CANADA/NEW ENGLAND
FLOW... LEADING TO VARIED WEIGHTING OF THOSE SOLNS AS THE PRIMARY
BASIS FOR THE FCST INTO DAY 6 FRI.  THE 00Z GFS AND SOME GEFS
MEMBERS WERE SOMEWHAT DEEPER WITH THE WRN TROUGH AT SOME FCST HRS
AND THE 00Z GFS TRENDS OUT OF PHASE WITH CONSENSUS OVER ERN CANADA
BY LATE THU-FRI.  NOTE THAT NEW ENGLAND/ERN CANADA ENSEMBLE SPREAD
EXPANDS CONSIDERABLY AROUND DAY 5 THU SO IT IS LIKELY THAT THE
FCST OVER THAT REGION REMAINS FAR FROM RESOLVED.  OTHER LESS
CONFIDENT ASPECTS OF THE FCST INCLUDE DIFFUSE WRN GULF INTO MS VLY
ENERGY ALOFT... SOME OF WHICH MAY TRY TO WORK ITS WAY EWD... AND
THE REMNANTS OF ERIKA WHICH MAY STILL HAVE MEANINGFUL EFFECTS OVER
PARTS OF THE EXTREME SOUTHEAST.  WITH THE LAST ADVISORY ON ERIKA
HAVING BEEN ISSUED... CONSULT THE NHC TROPICAL WEATHER OUTLOOK FOR
THE LATEST INFO REGARDING THE REMNANTS OF ERIKA.

BY DAY 7 SAT SOME TIMING DIFFS EMERGE WITH THE WRN TROUGH... THE
00Z ECMWF MEAN LEANING TOWARD THE SLOWER SIDE OF THE SPREAD.
CONSISTENCY OF RECENT ECMWF MEAN RUNS SUPPORTS A LITTLE MORE
WEIGHTING OF ITS FCST.  HOWEVER UPSTREAM NRN PAC FLOW IS BECOMING
A LITTLE MORE PROGRESSIVE TOWARD THE END OF THE PERIOD AND
TELECONNECTIONS RELATIVE TO THE CORE OF POSITIVE HGT ANOMALIES
NEAR JAMES BAY IN THE D+8 MEANS ALLOW FOR A WRN TROUGH AXIS THAT
COULD REACH A LITTLE FARTHER EWD.  THUS MAINTAINED SOME 06Z GEFS
MEAN WEIGHTING IN THE FCST AS WELL.


...SENSIBLE WEATHER HIGHLIGHTS...

PORTIONS OF THE SOUTHEAST SHOULD MONITOR THE REMNANTS OF ERIKA AS
ASSOC MSTR MAY SUPPORT AREAS OF LOCALLY HVY RNFL.  THE INITIAL
WEAKNESS FROM THE GULF COAST INTO THE MS VLY COULD ALSO ENCOURAGE
SOME CONVECTION FROM THE WRN-CNTRL GULF COAST EWD/NEWD.  MEANWHILE
THE PERSISTENT MEAN TROUGH NEAR/JUST INLAND FROM THE WEST COAST
ALONG WITH THE LEADING SFC FRONT SHOULD ENHANCE PCPN OVER PARTS OF
THE PAC NW/NRN ROCKIES AND NRN PLAINS/UPR MIDWEST.  EXPECT SOME
MONSOONAL ACTIVITY OVER THE SRN HALF OF THE ROCKIES BUT PERHAPS
WITH SOME DECREASE WITH TIME.

THE UPR TROUGH WILL KEEP TEMPS WELL BELOW NORMAL OVER THE WEST...
ESPECIALLY FROM THE PAC NW INTO THE NRN ROCKIES WHERE MAX TEMP
ANOMALIES MAY BE AT LEAST MINUS 10-15F FOR ONE OR MORE DAYS.
FARTHER EWD THERE WILL BE A BROAD AREA OF WARM TEMPS WITH HIGHS
5-15F ABOVE NORMAL AND SOME NRN TIER MINS PSBLY REACHING 15-20F
ABOVE NORMAL.

RAUSCH

$$





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