499
FXUS21 KWNC 201931
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 20 2024
SYNOPSIS: MULTIPLE MODELS CONTINUE TO SHOW SURFACE HIGH PRESSURE SINKING
SOUTHWARD FROM CANADA INTO THE CENTRAL CONTIGUOUS U.S. (CONUS) AND INTERIOR
WEST, SUPPORTING INCREASED RISK FOR HAZARDOUS COLD ACROSS THE NORTH-CENTRAL
CONUS. ACROSS THE EASTERN CONUS, THERE IS SIGNIFICANTLY MORE UNCERTAINTY AMONG
MODEL GUIDANCE TODAY COMPARED TO YESTERDAY, ESPECIALLY REGARDING THE POTENTIAL
FOR UNSETTLED WEATHER ACROSS THE REGION LEADING TO DECREASED CONFIDENCE IN THE
POTENTIAL FOR ASSOCIATED HAZARDS IN TODAY’S OUTLOOK. A SLIGHT RISK OF HEAVY
PRECIPITATION IS DESIGNATED FOR HEAVY PRECIPITATION FOR PARTS OF THE OHIO,
TENNESSEE, AND MIDDLE AND LOWER MISSISSIPPI VALLEYS, AND SOUTHERN APPALACHIANS
ASSOCIATED WITH POTENTIAL LINGERING IMPACTS FROM A POSSIBLE STORM TRACKING
ACROSS THE EAST AT THE END OF WEEK-1 INTO THE ONSET OF WEEK-2. SLIGHT RISKS FOR
HEAVY SNOW INCLUDING LAKE EFFECT SNOW ARE HIGHLIGHTED ACROSS PARTS OF THE OHIO
VALLEY, GREAT LAKES AND NORTHEAST, AND HIGH WINDS ACROSS MUCH OF THE EASTERN
CONUS, SOUTHERN PLAINS, AND MIDDLE AND LOWER MISSISSIPPI VALLEY AT THE
BEGINNING OF THE PERIOD.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE NORTHERN
PLAINS, THU-SAT, NOV 28-NOV 30.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY, THU-WED, NOV 28-DEC 4.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE OHIO, TENNESSEE, AND MIDDLE
AND LOWER MISSISSIPPI VALLEYS, AND SOUTHERN APPALACHIANS, THU, NOV 28.
SLIGHT RISK OF PERIODS OF HEAVY SNOW INCLUDING LAKE EFFECT SNOW ACROSS PARTS OF
THE OHIO VALLEY, GREAT LAKES AND NORTHEAST, THU-SAT, NOV 28-30.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS MANY PARTS OF THE EASTERN CONUS,
SOUTHERN PLAINS, AND MIDDLE AND LOWER MISSISSIPPI VALLEY, THU-SAT, NOV 28-30.
DETAILED SUMMARY
FOR SATURDAY NOVEMBER 23 - WEDNESDAY NOVEMBER 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY NOVEMBER 28 - WEDNESDAY DECEMBER 04: THE GEFS AND ECENS ENSEMBLE
MEANS INDICATE AN AMPLIFIED TROUGH STRETCHING ACROSS THE EASTERN TWO-THIRDS OF
THE CONUS DURING WEEK-2, INITIALLY CENTERED OVER THE CENTRAL CONUS PROGRESSING
EASTWARD WITH TIME. THE CMCE ENSEMBLE MEAN REMAINS AN OUTLIER, INDICATING A
MUCH WEAKER PATTERN COMPARED TO THE OTHER MODELS. THERE IS INCREASED
UNCERTAINTY COMPARED TO YESTERDAY FOLLOWING AN INITIAL SURFACE LOW AND
ASSOCIATED FRONTS ANTICIPATED DURING THE END OF WEEK-1 AS THE FRONTAL SYSTEM
EXITS THE EAST COAST BY OR DURING THE ONSET OF WEEK-2. THE MID-LEVEL PATTERN
GENERALLY FAVORS UNSETTLED WEATHER ACROSS THE EAST DURING THE BUSY THANKSGIVING
TRAVEL PERIOD, ALTHOUGH THERE IS SIGNIFICANT UNCERTAINTY REGARDING THE
SPECIFICS OF POTENTIAL SURFACE LOWS, FRONTS, AND ASSOCIATED IMPACTS.
SURFACE HIGH PRESSURE IS PREDICTED TO SINK SOUTHWARD FROM WESTERN CANADA INTO
THE CENTRAL CONUS AND INTERIOR WEST AT THE ONSET OF WEEK-2, BRINGING COLD
ARCTIC AIR INTO THE REGION. A SLIGHT RISK (20-40% CHANCE) OF MUCH BELOW NORMAL
TEMPERATURES IS MAINTAINED FOR PARTS OF THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY THROUGHOUT WEEK-2. A MODERATE RISK (40-60% CHANCE) IS POSTED
FOR THE NORTHERN PLAINS, NOV 28-30, WHERE THE PROBABILISTIC EXTREMES TOOLS
(PETS) INDICATE AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES FALLING TO THE
LOWEST 15TH PERCENTILE CLIMATOLOGICALLY AND -10 DEG F, WITH WIND CHILL
TEMPERATURES POTENTIALLY BEING EVEN LOWER.
THERE IS SIGNIFICANT UNCERTAINTY AMONG MODELS REGARDING THE TIMING AND
EVOLUTION OF A POTENTIAL SURFACE LOW TRACKING ACROSS THE EASTERN CONUS AT THE
END OF WEEK-1 INTO POTENTIALLY THE ONSET OF WEEK-2. A SLOWER TRACK MAY SUPPORT
LINGERING HEAVY PRECIPITATION, HEAVY SNOW, AND HIGH WINDS ACROSS PORTIONS OF
THE EAST AT THE BEGINNING OF WEEK-2. THEREFORE, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR PARTS OF THE OHIO, TENNESSEE, AND MIDDLE AND LOWER
MISSISSIPPI VALLEYS, AND SOUTHERN APPALACHIANS FOR DAY 8 (NOV 28). THIS RISK IS
PRIMARILY BASED ON WHERE THE ECENS PET SHOWS AT LEAST A 20% OF 3-DAY
PRECIPITATION (DAYS 8 TO 10, ALTHOUGH TIMING WOULD MOSTLY LIKELY BE FOR DAY 8)
TOTALS EXCEEDING THE 85TH PERCENTILE AND ONE INCH (GEFS INDICATES 0.75 INCHES),
AND SUPPORT FROM THE UNCALIBRATED ECENS AND RECENT DETERMINISTIC GFS AND ECMWF
SOLUTIONS.
PARTS OF THE EAST MAY CONTINUE TO HAVE INCREASED RISK OF HEAVY PRECIPITATION
DURING THE PERIOD BEYOND DAY 8 DUE TO POTENTIAL SURFACE LOWS AND ASSOCIATED
FRONTS, ALTHOUGH THERE IS TOO MUCH UNCERTAINTY AT THIS TIME TO SPECIFY ANY
ADDITIONAL AREAS OF RISK. A SLIGHT RISK FOR HEAVY SNOW INCLUDING LAKE EFFECT
SNOW IS HIGHLIGHTED ACROSS PARTS OF THE OHIO VALLEY, GREAT LAKES AND NORTHEAST,
NOV 28-30, ASSOCIATED WITH THE AFOREMENTIONED DEPARTING SURFACE LOW EXITING THE
NORTHEAST AT THE BEGINNING OF WEEK-2. THE UNCALIBRATED ECENS ENSEMBLE SHOWS AT
LEAST A 20% CHANCE OF SNOWFALL EXCEEDING 6 INCHES IN SOME OF THIS HIGHLIGHTED
RISK AREA.
A FRONT EXTENDING ACROSS THE GULF COAST IN ADDITION TO THE PREDICTED ACTIVE
PATTERN ACROSS THE EAST SUPPORTS A SLIGHT RISK (20-40%) OF EPISODIC HIGH WINDS
WHICH IS SLIGHTLY EXPANDED WESTWARD IN TODAY’S OUTLOOK COMPARED TO YESTERDAY,
ENCOMPASSING MUCH OF THE EASTERN THIRD OF THE CONUS, MIDDLE AND LOWER
MISSISSIPPI VALLEY, AND SOUTHERN PLAINS NOV 28-30. THE ECENS PETS SHOW SOME
AREAS EXPERIENCING WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 20 MPH.
A SERIES OF SURFACE LOWS ARE PREDICTED TO FORM OVER THE GULF OF ALASKA, WHICH
MAY BRING UNSETTLED WEATHER TO SOUTHEASTERN PORTIONS OF THE STATE. CONDITIONS
ARE NOT ANTICIPATED TO SUPPORT WIDESPREAD HAZARDS AT THIS TIME.
FORECASTER: MELISSA OU
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