329
FXUS21 KWNC 051757
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 05 2023
SYNOPSIS: A STORM SYSTEM FORECAST TO EJECT OUT OF THE ROCKY MOUNTAINS LATE IN
WEEK-1 IS LIKELY TO TRACK EAST TO THE EASTERN CONTIGUOUS U.S. (CONUS) BY THE
BEGINNING OF WEEK-2. THIS IS FORECAST TO BRING CHANCES FOR HEAVY PRECIPITATION
ALONG THE EASTERN CONUS. BELOW-NORMAL TEMPERATURES ARE FAVORED ACROSS PARTS OF
WESTERN ALASKA BUT HAZARDOUS TEMPERATURES ARE LESS LIKELY. ABOVE-NORMAL
PRECIPITATION REMAINS FAVORED IN THE PACIFIC NORTHWEST BUT DAILY PRECIPITATION
AMOUNTS ARE NOT LIKELY TO REACH HAZARDOUS CRITERIA.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE EAST COAST FROM MAINE TO FLORIDA,
FRI-SUN, OCT 13-15.
DETAILED SUMMARY
FOR SUNDAY OCTOBER 08 - THURSDAY OCTOBER 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY OCTOBER 13 - THURSDAY OCTOBER 19: AN AMPLIFIED 500-HPA HEIGHT
PATTERN IS FORECAST ACROSS NORTH AMERICA AND THE SURROUNDING AREAS DURING
WEEK-2. A DEEP TROUGH IS FORECAST ACROSS THE NORTHEAST PACIFIC BRINGING
TROUGHING AND NEGATIVE 500-HPA HEIGHT ANOMALIES TO PARTS OF WESTERN ALASKA AND
OFF SHORE OF THE PACIFIC NORTHWEST, RIDGING AND POSITIVE 500-HPA HEIGHT
ANOMALIES ARE FAVORED FROM THE ROCKY MOUNTAINS INTO THE PLAINS, AND TROUGHING
IS AGAIN FAVORED ACROSS THE EASTERN CONUS.
THERE ARE DISAGREEMENTS BETWEEN THE GEFS AND ECMWF ON THE PATH OF A LOW
PRESSURE SYSTEM THAT IS GOING TO EJECT OUT OF THE ROCKY MOUNTAINS LATE IN
WEEK-1 AS A RESULT OF RIDING DEVELOPING IN ACROSS THE ROCKIES. THE GEFS TRACKS
THIS SYSTEM NORTHEAST ACROSS THE PLAINS INTO THE GREAT LAKES AND NORTHEAST. THE
ECMWF BRINGS THIS STORM ACROSS THE GULF COAST AND SOUTHEAST AND THEN MOVES
NORTH ALONG THE ATLANTIC SEABOARD. IT LOOKS LIKELY THAT A STORM SYSTEM OF SOME
TYPE WILL DEVELOP IN THE EASTERN CONUS AND BRING POTENTIALLY HEAVY
PRECIPITATION EARLY IN THE PERIOD. THE GEFS PROBABILISTIC EXTREMES TOOL (PET)
INDICATES 20% CHANCES FOR PRECIPITATION EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE ACROSS PORTIONS OF THE MID-ATLANTIC AND NORTHEAST. MEANWHILE, THE
ECMWF PET MAINTAINS GREATER THAN 40% CHANCES FOR PRECIPITATION TO EXCEED THE
85TH PERCENTILE ACROSS LARGE PORTIONS OF THE SOUTHEAST AND 20% CHANCES INTO THE
MID-ATLANTIC AND NORTHEAST. RAW MODEL TOOLS ALSO SUPPORT PRECIPITATION AMOUNTS
EXCEEDING 1 INCH IN THESE REGIONS. THEREFORE, A BROAD SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR THE ENTIRE ATLANTIC SEABOARD FROM OCT 13-15.
HOWEVER, PINPOINTING WHERE THE HIGHEST IMPACTS WILL BE IS STILL UNCERTAIN AND
THEREFORE NO MODERATE SHAPES ARE CURRENTLY POSTED.
WITH INCREASED PRECIPITATION CHANCES EXPANDING ACROSS THE SOUTHEASTERN CONUS
AND BELOW-NORMAL TEMPERATURES FORECAST DURING THE WEEK-2 PERIOD, THE RAPID
ONSET DROUGHT (ROD) RISK HAZARD IS REMOVED. THE COMBINATION OF WETTER
CONDITIONS AND BELOW-NORMAL TEMPERATURES FAVORED REDUCE THE CHANCES FOR A RAPID
DEGRADATION OF DROUGHT CONDITIONS ACROSS THE TENNESSEE AND LOWER MISSISSIPPI
VALLEY DESPITE LIMITED PRECIPITATION IN THE PAST SEVERAL WEEKS AND VERY LOW
SOIL MOISTURE IN THESE REGIONS.
A TROUGH LOCATED OFF THE WEST COAST IS FAVORED TO PROMOTE ABOVE-NORMAL
PRECIPITATION IN THE PACIFIC NORTHWEST. THE GEFS AND ECMWF PETS INDICATE A 20%
CHANCE OF PRECIPITATION EXCEEDING THE 85TH PERCENTILE DURING MUCH OF THE
PERIOD. HOWEVER, 3 DAY PRECIPITATION AMOUNTS ARE FORECAST TO BE AROUND 1 INCH
OF PRECIPITATION ALONG THE WEST COAST. THESE AMOUNTS WOULD NOT BE HAZARDOUS IN
THESE REGIONS. THEREFORE, NO ASSOCIATED PRECIPITATION HAZARD IS POSTED AT THIS
TIME.
PERSISTENT MID-LEVEL TROUGHING FORECAST ACROSS ALASKA FAVORS BELOW-NORMAL
TEMPERATURES ACROSS MUCH OF THE STATE. THESE BELOW-NORMAL TEMPERATURES MAY HELP
TO FACILITATE RIVER-ICE FORMATION ACROSS PARTS OF INTERIOR ALASKA. THE ECMWF
AND GEFS PETS CONTINUE TO INDICATE AT LEAST A 20 PERCENT CHANCE OF MINIMUM
TEMPERATURES FALLING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE AND 20 DEG F
ACROSS MUCH OF WESTERN MAINLAND ALASKA AND THE ALASKA PENINSULA ON DAY 8.
HOWEVER, RAW DYNAMICAL GUIDANCE INDICATES TEMPERATURES TO REMAIN ABOVE 20 DEG F
ON OCT 13 WHICH IS UNLIKELY TO BE HAZARDOUS AT THIS TIME. THEREFORE, THE SLIGHT
RISK OF MUCH BELOW NORMAL TEMPERATURES HAS BEEN DISCONTINUED.
FORECASTER: RYAN BOLT
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