817
FXUS21 KWNC 131800
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 13 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE OVER THE BERING SEA IS FAVORED TO STRENGTHEN,
PUSHING THE STORM TRACK SOUTH AND REDUCING THE THREAT FOR HAZARDOUS WEATHER FOR
SOUTHEASTERN ALASKA. MEANWHILE, MODEL SOLUTIONS TODAY DEPICT STRONGER
MID-LEVEL LOW PRESSURE OVER THE SOUTHEASTERN CONTIGUOUS U.S. (CONUS) RELATIVE
TO YESTERDAY, RESULTING IN AN INCREASED CHANCE FOR HEAVY PRECIPITATION EARLY IN
WEEK-2.
HAZARDS
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST U.S.,
SAT-SUN, OCT 21-22.
DETAILED SUMMARY
FOR MONDAY OCTOBER 16 - FRIDAY OCTOBER 20:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY OCTOBER 21 - FRIDAY OCTOBER 27: THERE IS GOOD AGREEMENT AMONG THE
GEFS, ECMWF, AND CMCE SOLUTIONS FEATURING A NOTICEABLE SHIFT IN THE SYNOPTIC
PATTERN AS DEPICTED IN 500-HPA HEIGHT ANOMALIES AT THE ONSET OF WEEK-2. THE
MODELS SIGNIFICANTLY INCREASE THE STRENGTH OF AN ANOMALOUS RIDGE OVER THE
BERING SEA, DISPLACING THE MEAN STORM TRACK SOUTHWARD. AS A RESULT, WEEK-2
HEAVY PRECIPITATION AND HIGH WIND HAZARDS THAT WERE POSTED FOR ALASKA YESTERDAY
HAVE BEEN REMOVED FROM THE OUTLOOK TODAY. MEANWHILE OVER THE CONUS, THE MODELS
ARE ALSO IN AGREEMENT ON A DEEPER TROUGH OVER THE EASTERN CONUS AT THE
BEGINNING OF WEEK-2 RELATIVE TO YESTERDAY. THIS WOULD FAVOR A STRONGER SURFACE
LOW TO FORM AND HIGHER RAINFALL TOTALS OVER THE SOUTHEAST U.S. EARLY IN THE
FORECAST PERIOD.
THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A
20% CHANCE FOR 3-DAY RAINFALL TO EXCEED THE 85TH PERCENTILE AND 1 INCH TOTAL
FOR A SWATH ROUGHLY FROM THE FLORIDA PANHANDLE NORTHEASTWARD ALONG AND EAST OF
THE APPALACHIANS TO CENTRAL VIRGINIA FOR OCT 21-22. UNCALIBRATED OUTPUT FROM
THE ECMWF SUGGESTS THAT THE BULK OF THIS ENHANCED RAIN WILL OCCUR ON OCT 21,
BUT THE PREPONDERANCE OF MODEL GUIDANCE CANNOT RULE OUT THE POTENTIAL FOR
POTENTIALLY HAZARDOUS RAINFALL ON THE 22ND AS WELL. THE ECMWF AND CMCE PETS
ALSO FAVOR THE NORTHERN EXTENT OF ENHANCED RAINFALL TO EXTEND AS FAR NORTH AS
NEW ENGLAND, BUT GIVEN THE LOWER POTENTIAL FOR HAZARDOUS 3-DAY RAINFALL TOTALS
AND GREATER UNCERTAINTY REGARDING THE TRACK OF THE SURFACE LOW ASSOCIATED WITH
THE MID-LEVEL TROUGH, A SLIGHT RISK FOR HEAVY PRECIPITATION IS CONFINED TO
PORTIONS OF THE SOUTHEAST U.S. FOR OCT. 21-22. DEPENDING ON THE TRACK OF THE
SURFACE LOW THERE IS THE POTENTIAL FOR COASTAL FLOODING TO OCCUR FROM THE
CAROLINAS NORTHWARD TO THE MOUTH OF THE CHESAPEAKE.
AS THIS SURFACE LOW TRACKS OVER THE EAST COAST QUICKLY AND THE MID-LEVEL TROUGH
FLATTENS AS THE PERIOD PROGRESSES, MOSTLY ZONAL FLOW IS FAVORED BY THE MODEL
ENSEMBLES FOR THE REMAINDER OF THE WEEK-2 PERIOD. FORECAST TEMPERATURE
ANOMALIES THROUGHOUT THE FORECAST PERIOD ARE GENERALLY SMALL, AND NO MAJOR
INFLUXES OF COLDER AIR FROM HIGHER LATITUDES ARE LIKELY UNDER THE DEPICTED FLOW
REGIME. THE PETS ALL INDICATE SLIGHTLY INCREASED CHANCES FOR WINDS OVER THE
GREAT PLAINS TO EXCEED THE 85TH PERCENTILE THROUGHOUT WEEK-2, BUT PROBABILITIES
OF ACTUAL WIND SPEEDS TO EXCEED 25MPH ARE QUITE LOW, SO NO HIGH WIND HAZARD IS
POSTED AT THIS TIME. LATE IN THE FORECAST PERIOD THE AMPLIFIED RIDGE OVER THE
BERING SEA IS FAVORED TO SHIFT SOUTHEASTWARD, POTENTIALLY SETTING UP A COLD AIR
INCURSION INTO THE WESTERN CONUS LATE IN WEEK-2, BUT UNCERTAINTY ON THIS IS
HIGH SO NO HAZARD IS POSTED AT THIS TIME.
FORECASTER: DANNY BARANDIARAN
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