Prognostic Meteorological Discussion
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FXUS02 KWBC 271555
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1154 AM EDT THU AUG 27 2015

VALID 12Z SUN AUG 30 2015 - 12Z THU SEP 03 2015

...ERIKA MAY THREATEN FL/SERN COAST BY NEXT WEEK WITH
WINDS/WAVES/HEAVY RAINS...

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

EXPECT THE LARGE SCALE PATTERN TO FEATURE A FAIRLY AMPLIFIED WEST
COAT MEAN TROUGH AND BROAD RIDGE DOWNSTREAM WITH A HINT OF MEAN
TROUGHING OVER THE CANADIAN MARITIMES/NEW ENGLAND.  EMBEDDED
WITHIN THE OVERALL MEAN RIDGE... GUIDANCE SHOWS MULTIPLE PIECES OF
MID LVL ENERGY INITIALLY WITHIN A WEAKNESS FROM THE GRTLKS TO
CNTRL-WRN GULF COAST.  UNCERTAINTY OVER THE FINER DETAILS OF FLOW
ALOFT OVER THE ERN CONUS/WRN ATLC BY THE LATTER HALF OF THE PERIOD
LEADS TO BELOW AVG CONFIDENCE FOR THE ULTIMATE TRACK OF ERIKA.

CONSULT LATEST NATIONAL HURRICANE CENTER PRODUCTS FOR FURTHER INFO
REGARDING T.S. ERIKA WHICH IS FCST TO STRENGTHEN TO HURCN STATUS
BY EARLY NEXT WEEK.  EXTRAPOLATION OF THE 1500 UTC ADVISORY LEADS
TO A DAYS 6-7 WED-THU TRACK OFF THE SERN COAST... WITH A SOMEWHAT
SLOWER TREND RELATIVE TO CONTINUITY BASED ON A SWD ADJUSTMENT FOR
INITIAL POSN AS PER THE AFOREMENTIONED ADVISORY.  NOTE THAT
ENSEMBLE SPREAD IS QUITE BROAD ALREADY BY DAY 4 MON AND EXPANDS
FURTHER THEREAFTER.  OPERATIONAL SOLNS BECOME INCREASINGLY DIVERSE
AS WELL.  THIS IS NOT SURPRISING GIVEN THE RELATIVELY SMALLER
SCALE AND WEAK NATURE OF ONE OR MORE POTENTIALLY IMPORTANT SHRTWV
IMPULSES TO THE N AND W OF ERIKA.  AFTERNOON ISSUANCE OF WPC PROGS
WILL REFLECT 1700 UTC NHC/WPC COORDINATION FOR DAYS 6-7.

IN CONTRAST TO THE SITUATION OVER/NEAR THE SERN STATES...
MODEL/ENSEMBLE GUIDANCE DISPLAYS BETTER THAN AVG CLUSTERING WITHIN
THE WEST COAST MEAN TROUGH.  A LEADING SHRTWV SHOULD EJECT FROM
THE NORTHWEST DAY 3 SUN WITH A BRIEF FLATTENING OF THE TROUGH
BEFORE ANOTHER DEFINED SHRTWV SHARPENS THE TROUGH BY DAY 7 THU.
THERE IS SOMEWHAT MORE SPREAD WITH THE SHALLOW MEAN TROUGH THAT
MAY BRUSH NEW ENGLAND AND THE CANADIAN MARITIMES.

BASED ON REASONABLE CONSENSUS OVER THE WEST/NORTH THE STARTING
BLEND PRIMARILY ACCOUNTS FOR THE TRACK OF ERIKA BY WAY OF A
COMPROMISE PRIMARILY AMONG THE 12Z/26 ECMWF AND 00Z/06Z GFS INTO
DAY 5 TUE... WITH MINIMAL INCLUSION OF THE 00Z GEFS/ECMWF MEANS.
SOME 12Z/26 ECMWF AND 06Z GFS INPUT WAS MAINTAINED INTO DAYS 6-7
WED-THU WITH ENSMEAN WEIGHTING INCREASED SOMEWHAT COMPARED TO
EARLIER IN THE PERIOD.


...SENSIBLE WEATHER HIGHLIGHTS...

LOCATIONS ESPECIALLY OVER FLORIDA AND ALONG THE SERN COAST WILL
NEED TO MONITOR FCSTS FOR ERIKA WITH POTENTIAL IMPACTS INCLUDING
STRONG WINDS/HIGH WAVES/HVY RNFL.  RELATIVELY LOW PREDICTABILITY
OF FEATURES THAT MAY INFLUENCE THE STEERING/EVOLUTION OF ERIKA AT
THE EXTENDED TIME FRAME LEADS TO BELOW AVG CONFIDENCE IN
FORECASTING PRECISE EFFECTS AT PARTICULAR LOCATIONS AT THIS TIME.
THE LARGE SCALE PATTERN WILL FAVOR BELOW NORMAL HIGHS ALONG/INLAND
FROM THE WEST COAST WITH ONE OR MORE EPISODES OF ENHANCED RNFL
ALONG FAVORED TERRAIN OF THE PAC NW... AND FARTHER EWD A BROAD
AREA OF ABOVE NORMAL TEMPS FROM MOST OF THE PLAINS ACROSS THE
MIDWEST INTO THE NORTHEAST.  SOME LOCATIONS MAY SEE MULTIPLE DAYS
WITH PLUS 10F OR GREATER ANOMALIES.  A MEAN FRONTAL BNDRY MAY
SERVE AS A FOCUS FOR SOME CONVECTION OVER THE EXTREME NRN TIER...
MONSOONAL MSTR/SHRTWV IMPULSES WILL LIKELY SUPPORT PERIODS OF
CONVECTION OVER THE SRN HALF OF THE ROCKIES... AND A WEAK UPR LOW
MAY ENHANCE RNFL ALONG PORTIONS OF THE WRN HALF OF THE GULF COAST.
 SHRTWV ENERGY INITIALLY OVER THE GRTLKS COULD ALSO GENERATE SOME
SHWRS/TSTMS.

RAUSCH

$$




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