337
FXUS21 KWNC 061807
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 06 2023
SYNOPSIS: A STORM SYSTEM IS FORECAST TO BE EXITING OFF THE NORTHEAST AND
MID-ATLANTIC COAST AT THE ONSET OF WEEK-2 PROVIDING LINGERING CHANCES FOR HEAVY
PRECIPITATION EARLY IN THE PERIOD. ACROSS THE CENTRAL CONTIGUOUS U.S. (CONUS),
STRONG NORTHERLY MID-LEVEL FLOW IS FAVORED TO BRING CHANCES FOR MUCH BELOW
NORMAL TEMPERATURES INITIALLY ACROSS THE CENTRAL PLAINS, BEFORE PROGRESSING
EASTWARD TO THE OHIO AND TENNESSEE VALLEYS BRINGING INCREASED CHANCES FOR FROST
AND FREEZES TO THESE REGIONS. 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 NORTHEAST AND MID-ATLANTIC, SAT,
OCT 14.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE CENTRAL
PLAINS AND MIDDLE MISSISSIPPI VALLEY, SAT-SUN, OCT 14-15.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE MIDDLE
MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, SUN-WED, OCT 15-18.
DETAILED SUMMARY
FOR MONDAY OCTOBER 09 - FRIDAY OCTOBER 13:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY OCTOBER 14 - FRIDAY OCTOBER 20: 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
OFFSHORE 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.
THE GEFS AND ECMWF ARE IN BETTER AGREEMENT ON THE EVOLUTION OF AN AREA OF
SURFACE LOW PRESSURE PROGRESSING ACROSS THE COUNTRY IN WEEK-1. BY THE ONSET OF
WEEK-2, THIS SYSTEM IS FORECAST TO BE EXITING OFF THE NORTHEAST COAST. THE
ECMWF PROBABILISTIC EXTREMES TOOL (PET) SHOWS A 20 PERCENT OF PRECIPITATION
EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 1 INCH DURING THE FIRST THREE
DAYS OF THE FORECAST PERIOD FROM THE MID-ATLANTIC NORTH THROUGH NEW ENGLAND.
THE GEFS PET IS LESS EXPANSIVE BUT MAINTAINS SIMILAR CHANCES FOR EXCEEDING THE
85TH PERCENTILE AND 1 INCH ALONG THE IMMEDIATE COASTLINE. RAW DETERMINISTIC
TOOLS INDICATE MOST PRECIPITATION WOULD LIKELY FALL ON DAY 8. THEREFORE, A
SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR OCT 14 FROM THE MID-ATLANTIC
THROUGH NEW ENGLAND.
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.
WITH RIDGING BUILDING INTO THE ROCKIES, NORTHERLY FLOW IS FAVORED INITIALLY
ACROSS THE PLAINS BEFORE PROGRESSING EASTWARD BY THE MIDDLE OF THE PERIOD.
SURFACE HIGH PRESSURE IS ALSO FAVORED TO BE IN PLACE ACROSS THE PLAINS
INITIALLY AND THEN EXPAND FURTHER EAST OVER TIME. THIS IS LIKELY TO BRING
CONDITIONS FOR COOL NIGHTS ACROSS THE REGION. THE GEFS AND ECMWF PETS INDICATE
20 PERCENT CHANCES FOR TEMPERATURES TO FALL BELOW THE 15TH CLIMATOLOGICAL
PERCENTILE AND 40 DEG F ACROSS THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY
WITH SCATTERED CHANCES OF FALLING BELOW 32 DEG F. FURTHER NORTH, TEMPERATURES
ARE LESS LIKELY TO FALL BELOW THE 15TH PERCENTILE AND MORE LIKELY TO HAVE
ALREADY SEEN AN END TO THE GROWING SEASON. THEREFORE, A SLIGHT RISK OF MUCH
BELOW NORMAL TEMPERATURES IS POSTED FOR THE CENTRAL PLAINS AND MIDDLE
MISSISSIPPI VALLEY FOR OCT 14-15. AS THE PERIOD PROGRESSES THE BULK OF THE COLD
AIR MOVES EAST WITH BOTH THE GEFS AND ECMWF PETS INDICATING CHANCES FOR
TEMPERATURES TO FALL BELOW THE 15TH PERCENTILE AND 40 DEG F ACROSS MUCH OF THE
OHIO AND TENNESSEE VALLEYS. THEREFORE, A SECOND AREA FOR A SLIGHT RISK OF MUCH
BELOW NORMAL TEMPERATURES IS POSTED FOR THESE REGIONS FROM OCT 15-18.
PERSISTENT MID-LEVEL TROUGHING FORECAST SOUTH OF 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. HOWEVER,
THESE TEMPERATURES ARE UNLIKELY TO REACH HAZARDOUS THRESHOLDS FOR THIS TIME OF
YEAR. IN SOUTHEAST AND THE SOUTH-CENTRAL MAINLAND, ABOVE-NORMAL PRECIPITATION
IS FAVORED. THE GEFS PET IS SHOWING 20 PERCENT CHANCES OF 3 DAY PRECIPITATION
AMOUNTS EXCEEDING THE 85TH PERCENTILE. HOWEVER, THESE TOTALS ARE LIKELY TO BE
BELOW 3 INCHES OF PRECIPITATION IN A VERY WET TIME OF YEAR ACROSS SOUTHERN
ALASKA. MEANWHILE, THE ECMWF PET DOES NOT FORECAST A 20 PERCENT CHANCE OF
EXCEEDING THE 85TH PERCENTILE OVER MOST OF SOUTHERN ALASKA. THEREFORE, NO
PRECIPITATION HAZARD IS POSTED AT THIS TIME.
FORECASTER: RYAN BOLT
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