303
FXUS21 KWNC 151932
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 15 2024
SYNOPSIS: MULTIPLE MODEL ENSEMBLES DEPICT DEEP LOW PRESSURE AT THE SURFACE AND
ALOFT OVER THE NORTHEAST U.S. AT THE OUTSET OF WEEK-2, WHICH HAS THE POTENTIAL
TO BRING LOCALLY HEAVY SNOWFALL AND STRONG WINDS TO PORTIONS OF THE EASTERN
CONTIGUOUS U.S. (CONUS) AS WELL AS A SHOT OF COLD AIR TO PORTIONS OF THE
SOUTHEASTERN CONUS, BRINGING THE POTENTIAL FOR THE FIRST FREEZE OF THE SEASON
FOR THE REGION. ENHANCED ONSHORE FLOW AND ASSOCIATED MOISTURE TRANSPORT IS
FAVORED FOR PORTIONS OF THE WEST COAST, BRINGING POTENTIALLY HEAVY
PRECIPITATION NEAR THE COAST AND HEAVY SNOW FURTHER INLAND.
HAZARDS
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE LOWER MISSISSIPPI
VALLEY, TENNESSEE VALLEY, MID-ATLANTIC, AND SOUTHEAST U.S., SAT-SUN, NOV 23-24.
MODERATE RISK OF HEAVY SNOW FOR EASTERN SHORES OF LAKES ERIE AND ONTARIO, SAT,
NOV 23.
MODERATE RISK OF HEAVY SNOW FOR PORTIONS OF THE ALLEGANY FRONT, SAT, NOV 23.
SLIGHT RISK OF HEAVY SNOW FOR MUCH OF THE GREAT LAKES, AS WELL AS PORTIONS OF
THE OHIO VALLEY, CENTRAL APPALACHIANS, AND NORTHEAST U.S., SAT-MON, NOV 23-25.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES,
SAT-WED, NOV 23-27.
SLIGHT RISK OF HEAVY SNOW FOR THE SIERRA NEVADAS, KLAMATH MOUNTAINS AND CASCADE
RANGE, SAT-WED, NOV 23-27.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, SAT-WED, NOV 23-27.
MODERATE RISK OF HIGH WINDS FOR MUCH OF THE GREAT LAKES, AS WELL AS PORTIONS OF
THE OHIO VALLEY, CENTRAL APPALACHIANS AND NORTHEAST U.S., SAT-SUN, NOV 23-24.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE NORTHEASTERN CONUS, SAT-MON, NOV
23-25.
DETAILED SUMMARY
FOR MONDAY NOVEMBER 18 - FRIDAY NOVEMBER 22:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY NOVEMBER 23 - FRIDAY NOVEMBER 29: ENSEMBLE SOLUTIONS FROM THE GEFS
AND ECENS BOTH DEPICT A MATURE AND STRONG MID-LATITUDE CYCLONE OVER THE
NORTHEAST U.S. AT THE OUTSET OF WEEK-2. THIS SYSTEM IS THE PRODUCT OF STRONG
LEE CYCLOGENESIS WHICH IS EXPECTED TO BRING HAZARDOUS WEATHER TO THE GREAT
PLAINS DURING WEEK-1. MODEL CONSENSUS FAVORS THE SURFACE LOW TO BECOME OCCLUDED
AT THE OUTSET OF WEEK-2, LINGERING OVER THE GREAT LAKES FOR SEVERAL DAYS. MODEL
GUIDANCE HAS CONSISTENTLY INDICATED THIS TO BE A POTENT STORM SYSTEM WITH
SIGNIFICANT POTENTIAL TO GENERATE A VARIETY OF HAZARDOUS WEATHER CONDITIONS
SPREAD OUT OVER MUCH OF THE U.S. EAST OF THE ROCKIES.
ENSEMBLE AND DETERMINISTIC MODEL SOLUTIONS CONTINUE TO FAVOR AN OCCLUDED LOW
PRESSURE SYSTEM WINDING OVER ONTARIO AND NEW ENGLAND EARLY IN THE WEEK-2
PERIOD, RESULTING IN A PROLONGED PERIOD OF WESTERLY TO NORTHWESTERLY SURFACE
FLOW OVER THE GREAT LAKES, WHICH ARE AT OR NEAR RECORD HIGH SURFACE WATER
TEMPERATURES. COLD AIR ALOFT RESULTS IN VERY STEEP LAPSE RATES, FURTHER
CONTRIBUTING TO FAVORABLE LAKE-EFFECT SNOW CONDITIONS. CONSENSUS AMONG MODELS
IS FOR THIS FAVORABLE SETUP TO BE AT ITS STRONGEST LATE IN WEEK-1 AND
POTENTIALLY EARLY IN WEEK-2, THEREFORE A MODERATE RISK FOR HEAVY SNOW IS POSTED
FOR EASTERN SHORES OF LAKES ERIE AND ONTARIO FOR NOV 23. ADDITIONALLY, MODEL
SOLUTIONS HAVE BEEN STEADILY INCREASING THE SIGNAL FOR HEAVY SNOWFALL OVER THE
ALLEGHENY FRONT SO A MODERATE RISK FOR HEAVY SNOW IS POSTED THERE AS WELL FOR
NOV 23, WHILE A BROADER SLIGHT RISK OF HEAVY SNOW IS POSTED FOR THE GREAT
LAKES, AND PORTIONS OF THE OHIO VALLEY, CENTRAL APPALACHIANS AND NORTHEAST U.S.
FOR NOV 23-25. SURFACE TEMPERATURES ARE FORECAST TO BE NEAR FREEZING, THIS
INCREASES UNCERTAINTY REGARDING SNOW TOTALS WITH RAIN LIKELY MIXING WITH SNOW
AT TIMES, AND MAY MAKE FOR SLOPPY CONDITIONS ACROSS THE LAKE EFFECT SNOW BELTS.
WITH A CONCURRENT ENHANCED POTENTIAL FOR HIGH WINDS THE POTENTIAL FOR EXCESSIVE
SNOW ACCUMULATIONS MIGHT BE FURTHER REDUCED, BUT INSTEAD IS REPLACED WITH A
POTENTIAL FOR BLIZZARD CONDITIONS.
THE PROBABILISTIC EXTREMES TOOLS (PETS) FOR THE ECMWF CONTINUES TO SIGNAL THE
POTENTIAL FOR HIGH WINDS OVER THE NORTHEAST U.S. AT THE OUTSET OF WEEK-2,
INDICATING AT LEAST A 20% PROBABILITY OF MAXIMUM WIND SPEEDS EXCEEDING THE 85TH
PERCENTILE FOR MUCH OF THE EASTERN CONUS. DETERMINISTIC MODEL SOLUTIONS ALSO
CONSISTENTLY DEPICT STRONG SURFACE PRESSURE GRADIENTS ASSOCIATED WITH THIS
STORM SYSTEM. THE GFS DETERMINISTIC RUNS DESCRIBED ABOVE ALSO DEPICT STRONG
SURFACE PRESSURE GRADIENTS OVER MUCH OF THE NORTHEASTERN CONUS EARLY IN THE
FORECAST PERIOD. THUS, A SLIGHT RISK (20-40 PERCENT CHANCE) FOR HIGH WINDS
REMAINS FOR MUCH OF THE NORTHEASTERN CONUS FOR NOV 23-25. FURTHERMORE, A
MODERATE RISK (40-60 PERCENT CHANCE) FOR HIGH WINDS IS POSTED FOR MUCH OF THE
GREAT LAKES AS WELL AS PORTIONS OF THE OHIO VALLEY, CENTRAL APPALACHIANS, AND
NORTHEAST U.S., FOR NOV 23-24, WHERE MODEL GUIDANCE DEPICTS VERY TIGHT SURFACE
PRESSURE GRADIENTS.
ANOMALOUSLY COLD AIR IS FAVORED TO BE ASSOCIATED WITH THE UPPER LEVEL TROUGH
OVER THE CENTRAL CONUS, BRINGING POTENTIALLY IMPACTFUL MINIMUM TEMPERATURES TO
PORTIONS OF THE SOUTHERN PLAINS. THE GEFS AND ECENS PETS BOTH INDICATE AT LEAST
20% PROBABILITIES OF MINIMUM TEMPERATURES FALLING BELOW THE 15TH PERCENTILE
OVER MUCH OF THE SOUTHEASTERN CONUS EARLY IN WEEK-2. ADDITIONALLY, BOTH PETS
INDICATE THE POTENTIAL FOR FROST CONDITIONS AS FAR SOUTH AS THE GULF COAST AND
INTO THE NORTHERN FLORIDA PENINSULA, THEREFORE A SLIGHT RISK FOR MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR PORTIONS OF THE LOWER MISSISSIPPI
VALLEY AND MID-ATLANTIC, AS WELL AS MUCH OF THE SOUTHEAST U.S. FOR NOV 23-24.
AT THE OUTSET OF WEEK-2 ENSEMBLE SOLUTIONS DEPICT A WEAK MID-LEVEL TROUGH OVER
THE WEST COAST AND ASSOCIATED LOW PRESSURE SYSTEM NEAR THE COAST OF BRITISH
COLUMBIA. THESE FEATURES PERSIST WELL INTO WEEK-2 BRINGING POTENTIALLY HEAVY
PRECIPITATION TO COASTAL AREAS AND HEAVY SNOW FURTHER INLAND. THE ECMWF AND
GEFS PETS BOTH INDICATE AT LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION
TOTALS TO EXCEED THE 85TH PERCENTILE AND AT LEAST 1 INCH FOR NOV 23-27,
WARRANTING A SLIGHT RISK OF HEAVY PRECIPITATION TO BE POSTED FOR COASTAL
PORTIONS OF THE PACIFIC NORTHWEST AND CALIFORNIA NORTH OF MONTERREY BAY FOR NOV
23-27. ADDITIONALLY, THE GEFS PETS INDICATES THE POTENTIAL FOR 3-DAY SNOW WATER
EQUIVALENT (SWE) ACCUMULATIONS TO EXCEED THE 85TH PERCENTILE AND AT LEAST 0.5
INCH (LIQUID EQUIVALENT), WITH LOCALLY HIGHER AMOUNTS POSSIBLE ALONG THE
COASTAL RANGES AS WELL AS PORTIONS OF THE INTERMOUNTAIN WEST. THEREFORE A
SLIGHT RISK FOR HEAVY SNOW IS POSTED FOR THE SIERRA NEVADA, KLAMATH, AND
CASCADE RANGES, AS WELL AS MUCH OF THE NORTHERN AND CENTRAL ROCKIES FOR NOV
23-27.
FORECASTER: DANNY BARANDIARAN
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