420
FXUS21 KWNC 211936
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 21 2023
SYNOPSIS: STRONG SURFACE LOW PRESSURE MOVES FROM THE BERING SEA INTO THE GULF
OF ALASKA DURING THE FORECAST PERIOD, RESULTING IN A STORMY FORECAST WITH THE
POTENTIAL FOR HIGH WINDS AND HEAVY PRECIPITATION FOR MUCH OF THE SOUTHERN COAST
OF ALASKA. A TRAILING COLD FRONT OVER THE SOUTHEASTERN CONTIGUOUS U.S.(CONUS)
INTERACTING WITH TROPICAL MOISTURE IS FAVORED TO BRING SOME POTENTIALLY HEAVY
PRECIPITATION FOR THE SOUTHEAST U.S. EARLY IN WEEK 2.
HAZARDS
SLIGHT RISK FOR HIGH WINDS FOR MUCH OF SOUTHERN ALASKA, FROM BRISTOL BAY
EASTWARD AND SOUTHWARD TO INCLUDE ALL OF THE SOUTHERN COAST AND THE ALASKA
PANHANDLE, WED-SUN, NOV 29-DEC 3.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST U.S.,
WED-THU, NOV 29-30.
DETAILED SUMMARY
FOR FRIDAY NOVEMBER 24 - TUESDAY NOVEMBER 28:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY NOVEMBER 29 - TUESDAY DECEMBER 05: ENSEMBLE MODEL SOLUTIONS FROM
THE ECMWF, GEFS, AND CMCE ALL DEPICT A STRONG SURFACE LOW IN THE BERING SEA AT
THE ONSET OF WEEK-2. THOUGH THERE ARE SOME DIFFERENCES, MODEL CONSENSUS MOVES
THIS LOW PRESSURE INTO THE GULF OF ALASKA BY THE END OF THE FORECAST PERIOD,
WEAKENING AS THE WEEK GOES ON. THIS FAVORS STORMY WEATHER ALONG THE SOUTHERN
COAST OF ALASKA, ESPECIALLY DURING THE FIRST HALF OF THE FORECAST PERIOD. THE
ECMWF AND GEFS PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A 20%
PROBABILITY OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE. PRECIPITATION
TOTALS FROM ENSEMBLE SOLUTIONS DO NOT EXCEED HAZARD THRESHOLDS, SO NO HAZARD IS
POSTED AT THIS TIME. HOWEVER, A SLIGHT RISK FOR HIGH WINDS IS POSTED FROM
BRISTOL BAY TO THE ALASKA PANHANDLE FOR NOV 29-DEC 3. THE ECMWF AND GEFS PETS
BOTH INDICATE AT LEAST 20% PROBABILITY OF WIND SPEEDS EXCEEDING THE 85TH
PERCENTILE AND WIND SPEEDS IN EXCESS OF 40MPH THROUGH DAY-12, AND ENSEMBLE
SOLUTIONS FOR SURFACE LOW PRESSURE INDICATE A STRONG PRESSURE GRADIENT
DIRECTING ONSHORE FLOW INTO THE SOUTHERN COAST THROUGHOUT THE WEEK-2 PERIOD.
MUDSLIDES HAVE BEEN RECENTLY REPORTED IN THE ALASKA PANHANDLE, AND THESE STRONG
WINDS WHEN COUPLED WITH ENHANCED PRECIPITATION HAS THE POTENTIAL TO EXACERBATE
CONDITIONS ON THE GROUND.
AS THE AFOREMENTIONED SURFACE LOW MOVES SOUTHWARD LATER IN THE FORECAST PERIOD,
HEAVIER PRECIPITATION IS DEPICTED ALONG THE WESTERN COAST OF THE CONUS. WHILE
THIS STORM IS ANTICIPATED TO HAVE HAZARDOUS IMPACTS FOR ALASKA, CONSENSUS FROM
A VARIETY OF TOOLS SUGGESTS THAT BY THE TIME IMPACTS FROM THIS STORM REACH THE
CONUS THEIR STRENGTH WILL BE MUCH DIMINISHED, SO NO HAZARDS ARE POSTED AT THIS
TIME FOR THE WEST COAST.
AT THE ONSET OF THE FORECAST PERIOD A TRAILING COLD FRONT OVER THE SOUTHEAST
U.S. IS DEPICTED IN ENSEMBLE SOLUTIONS. RETURN FLOW SOUTH OF THE BOUNDARY HAS
THE POTENTIAL TO TRANSPORT A MOIST TROPICAL AIRMASS FROM THE CARIBBEAN INTO THE
REGION, ENHANCING RAINFALL TO POTENTIALLY HAZARDOUS LEVELS. THE GEFS AND ECMWF
PETS BOTH INDICATE AT LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION EXCEEDING
THE 85TH PERCENTILE EARLY IN THE FORECAST PERIOD. THE ECMWF IS MORE BULLISH IN
THIS SCENARIO, DEPICTING WIDESPREAD 3-DAY RAINFALL TOTALS EXCEEDING 1 INCH OVER
THE SOUTHEAST U.S. THE GEFS IS LESS ENTHUSIASTIC ABOUT THIS SOLUTION, BUT IN
THE ABSENCE OF MORE CONVINCING EVIDENCE TO THE CONTRARY, THE SLIGHT RISK FOR
HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST U.S. POSTED YESTERDAY REMAINS
IN PLACE, COVERING NOV 29-30.
FORECASTER: DANNY BARANDIARAN
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