Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 270615
PREEPD

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

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

...ERIKA TO THREATEN FL AND VICINITY BY EARLY NEXT WEEK WITH
WINDS/WAVES/HEAVY RAINS...

...PATTERN OVERVIEW/SENSIBLE WEATHER THREATS AND GUIDANCE
EVALUATION AND PREFERENCES...

THE NATIONAL HURRICANE CENTER INDICATED THAT TROPICAL STORM ERIKA
WAS LOCATED NEAR 16.7N 60.2W AT 03 UTC...PACKING SUSTAINED WINDS
OF 40 KTS WITH GUSTS TO 50 KTS. ERIKA IS  FORECAST TO THREATEN FL
AND THE SE US COAST AT UPWARDS TO HURRICANE STRENGTH INTO EARLY
NEXT WEEK. PLEASE CONSULT NHC PRODUCTS FOR LATEST INFO REGARDING
ERIKA.

MODEL RUN TO RUN VARIANCE FOR ERIKA AND OVERALL FLOW
CHARACTERISTICS ACROSS THE MID-UPPER LATITUDES FROM THE PACIFIC
INTO/ACROSS NORTH AMERICA HAS NOT BEEN STELLAR RECENTLY...BUT MAY
BE SLOWLY IMPROVING. THE 03 UTC FORECAST FROM THE NHC SEEM A BEST
FIT WITH THE 12 UTC ECMWF...BUT I INCLUDED SOME 12 UTC ECMWF
ENSEMBLES AND CONTINUITY FOR THE WPC SURFACE PRESSURES/500 MB
PROGS TO ADDRESS LINGERING UNCERTAINTY AT LONGER TIME FRAMES TO
DAY 7. THIS SOLUTION SEEMS TO INCORPORATE WELL INTO A PREFERRED
MASS FIELD COMPOSITE 18 UTC GFS/GEFS AND 12 UTC ECMWF/UKMET/ECMWF
ENSEMBLE MEAN SOLUTION FOR THE REST OF THE LOWER 48.

AN AMPLIFIED AND UNSEASONABLY COOL/WET ERN PAC MEAN TROUGH IS
SLATED TO SETUP OVER THE NW US/US WEST COAST. POTENT EMBEDDED
SHORTWAVES LIFT NEWD OUT FROM THIS MEAN TROUGH...WITH THE NEXT IN
A SERIES ALSO DIGGING SEWD FROM THE NERN PACIFIC TO REINFORCE.
LEAD WARMING RIDGING SHIFTS EASTWARD OVER THE N-CENTRAL US THEN
GREAT LAKES...WHILE HOLDING OVER THE SWRN US WHERE ROTATING VORTS
AIDE MONSOONAL ACTIVITY. A COMBINATION OF TRAPPED PLAINS ENERGY
AND A LINGERING TROUGH/SHEAR AXIS OVER THE EAST MAY YIELD
WEAKNESSES OVER THE VICINITY OF THE OH VALLEY AND MID-LOWER MS
VALLEY. PRIMARY FCST UNCERTAINTIES STILL REVOLVE AROUND INDIVIDUAL
SHORTWAVES WITHIN THE ERN PAC/WEST COAST MEAN TROUGH...DETAILS OF
THE EAST-CENTRAL U.S. WEAKNESSES THAT MAY OFFER SOME LOCAL
CONVECTION...AND THE EXTENT OF RIDGING OVER THE ERN US NEXT WEEK.
THIS LATTER ISSUE WILL PLAY A ROLE IN THE ULTIMATE
EVOLUTION/TRACK/STRENGTH OF ERIKA.

SCHICHTEL

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