065
FXUS21 KWNC 201931
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 20 2023
SYNOPSIS: AS WEEK-2 STARTS, COLD AIR IS EXPECTED TO COVER THE EASTERN
CONTIGUOUS U.S. (CONUS), THE SOUTHERN PLAINS, AND MUCH OF THE ROCKIES. THE
FIRST FROST OR FREEZE OF THE SEASON COULD AFFECT DEEP SOUTH TEXAS CLOSE TO THE
MIDDLE OF WEEK-2 BEFORE TEMPERATURES MODERATE ACROSS MUCH OF THE CONUS
EXCLUDING THE NORTHEAST, WHERE BELOW-NORMAL TEMPERATURES ARE PREDICTED TO
PERSIST THROUGH THE PERIOD. IT IS EXPECTED TO BE A WET WEEK ALONG THE SOUTHERN
TIER OF STATES EAST OF THE ROCKIES, WITH A SLIGHT RISK FOR EXCESSIVE
PRECIPITATION IN THE SOUTHEAST EARLY IN THE PERIOD. FARTHER NORTH, A TIGHT
PRESSURE GRADIENT BETWEEN SURFACE LOW PRESSURE OVER SOUTHWESTERN ALASKA AND
HIGH PRESSURE OVER THE WESTERN CONUS, HIGH WINDS ARE POSSIBLE ALONG THE
SOUTHERN TIER OF MAINLAND ALASKA INTO THE MIDDLE OF WEEK-2.
HAZARDS
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IN DEEP SOUTH TEXAS, THU-FRI, NOV
30 - DEC 1.
SLIGHT RISK OF HEAVY PRECIPITATION IN PARTS OF THE SOUTHEAST, TUE-THU, NOV
28-30.
SLIGHT RISK OF HIGH WINDS IN PARTS OF SOUTHERN ALASKA, TUE-FRI, NOV 28 - DEC 1.
DETAILED SUMMARY
FOR THURSDAY NOVEMBER 23 - MONDAY NOVEMBER 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY NOVEMBER 28 - MONDAY DECEMBER 04: COLD SURFACE HIGH PRESSURE
ORIGINATING IN NORTHERN CANADA IS EXPECTED TO EXTEND TO MOST OF THE ROCKIES,
SOUTHERN PLAINS, AND THE EASTERN CONUS WHEN WEEK-2 STARTS. THE EUROPEAN
ENSEMBLE MEAN IS COLDER THAN THE GEFS, AND KEEPS BELOW NORMAL TEMPERATURES IN
PLACE LONGER. THE GEFS PROBABILISTIC EXTREMES TOOL (PET) SHOWS MODEST ODDS FOR
TEMPERATURES FALLING BELOW THE CLIMATOLOGICAL 15TH PERCENTILE ACROSS THE
CENTRAL AND EASTERN CONUS, WITH CHANCES TOPPING OUT BETWEEN 20 AND 30 PERCENT
ON DAYS 10 AND 11 (THU-FRI, NOV 30 - DEC 1). THE EUROPEAN ENSEMBLE PET IS
SOMEWHAT MORE ROBUST, SHOWING ODDS OF 30 TO 40 PERCENT FOR TEMPERATURES BELOW
THE 15TH PERCENTILE IN THE SOUTHERN HALF OF THE GREAT PLAINS DURING THE FIRST
HALF OF THE PERIOD, AND CHANCES FOR SIMILAR READINGS EXCEEDING 40 PERCENT
ACROSS PORTIONS OF THE NORTHEAST DAYS 9 AND 10 (WED-THU, NOV 29-30). THE
EUROPEAN PET KEEPS ELEVATED ODDS FOR UNUSUALLY COLD WEATHER IN THE NORTHEAST
UNTIL LATE WEEK-2. THE CANADIAN PET IS ORIENTED DIFFERENTLY, KEEPING ELEVATED
CHANCES FOR MUCH BELOW NORMAL TEMPERATURES IN THE SOUTHERN HALF OF THE GREAT
PLAINS THROUGH MOST OF WEEK-2. THE LACK OF EXCEPTIONALLY COLD CROSS-POLAR AIR
AND THE DISAGREEMENT AMONG THE TOOLS PRECLUDES THE POSTING OF ANY ASSOCIATED
HAZARD, EXCEPT FOR A SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES IN DEEP
SOUTH TEXAS ON DAYS 10-11 (NOV 30 - DEC 1) DUE TO GOOD AGREEMENT BETWEEN THE
EUROPEAN AND CANADIAN ENSEMBLE PET TOOLS INDICATING THE INCREASED POTENTIAL OF
THE REGION EXPERIENCING ITS FIRST FROST OR FREEZE OF THE SEASON.
MODEL GUIDANCE IS SHOWING AN INCREASE IN MID-LEVEL DISTURBANCES MOVING ACROSS
THE SOUTHERN TIER OF STATES EAST OF THE ROCKIES. MORE THAN ONE DISTURBANCE IS
EXPECTED TO TRIGGER PRECIPITATION ACROSS THE REGION DURING WEEK-2, WITH THE
MODELS AND DERIVED TOOLS BEING CONSISTENT IN SHOWING ABOVE-NORMAL PRECIPITATION
ACROSS THE REGION FOR THE PERIOD AS A WHOLE. WHETHER OR NOT PRECIPITATION RATES
EXCEED HAZARDOUS THRESHOLDS, HOWEVER, IS MUCH LESS CERTAIN. THE GEFS AND
CANADIAN ENSEMBLE PET TOOLS SHOW SLIGHTLY ELEVATED CHANCES FOR PRECIPITATION
TOTALS TO EXCEED THE 85TH PERCENTILE AT VARIOUS TIMES DURING THE PERIOD, BUT
THE PET DERIVED FROM THE EUROPEAN ENSEMBLE IS MUCH MORE ROBUST EARLY IN THE
PERIOD, SHOWING SUBSTANTIALLY-ELEVATED ODDS FOR PRECIPITATION TO EXCEED BOTH
THE 85TH PERCENTILE AND ONE-INCH THRESHOLDS IN THE SOUTHEAST FOR THE FIRST 3
DAYS OF WEEK-2. A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR PARTS OF
THIS AREA DURING TUE-THU NOV 28-30 WHERE THE EUROPEAN PET TOOL SHOWS GREATER
THAN 40 PERCENT CHANCES FOR AMOUNTS EXCEEDING THE 85TH PERCENTILE, AND THE
CANADIAN- AND GEFS-BASED PET INDICATING ODDS FOR SIMILAR TOTALS EXCEEDING 20
PERCENT.
THE LATEST EUROPEAN ENSEMBLE MEANS PUSH MOISTURE CONSIDERABLY FARTHER NORTH
THAN OTHER GUIDANCE DURING THE FIRST HALF OF WEEK-2,MAINTAINING COLDER AIR
ACROSS THE NORTHEAST AT THE SAME TIME. THIS SUGGESTS ENHANCED CHANCES FOR
ACCUMULATING SNOW IN AT LEAST PART OF THE NORTHEAST DURING THE FIRST HALF OF
THE PERIOD, INCLUDING THE LOWER ELEVATIONS AND PERHAPS PORTIONS OF THE I-95
CORRIDOR. AT THIS TIME, HOWEVER, OTHER GUIDANCE IS NOT IN AGREEMENT, THUS NO
HAZARD IS POSTED AT THIS TIME.
BELOW NORMAL 500-HPA HEIGHTS WEST OF MAINLAND ALASKA ARE EXPECTED TO KEEP ONE
OR MORE SURFACE LOW PRESSURE SYSTEMS MEANDERING SLOWLY FROM THE SOUTHERN BERING
SEA INTO THE NORTH PACIFIC JUST SOUTH OF SOUTHWESTERN MAINLAND ALASKA. AT THE
SAME TIME, SURFACE HIGH PRESSURE IS EXPECTED TO COVER WESTERN NORTH AMERICA.
THE ANTICIPATED PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS INCREASES THE
LIKELIHOOD FOR HIGH WINDS ALONG PART OF THE SOUTHERN TIER OF THE STATE. THIS
THREAT IS LIKELY TO CONTINUE INTO THE MIDDLE OF THE PERIOD BEFORE THE PRESSURE
GRADIENT WEAKENS AND THE CHANCES FOR HIGH WINDS DECLINES. ALL THREE
ENSEMBLE-BASED PETS SHOW MORE THAN A 40 PERCENT CHANCE FOR HIGH SUSTAINED WINDS
EXCEEDING THE 85TH PERCENTILE FROM KODIAK ISLAND AND THE KENAI PENINSULA
EASTWARD TO NEAR SKAGWAY AND JUNEAU FOR THE FIRST THREE DAYS OF THE PERIOD, AND
ALL THREE ENSEMBLE MEANS KEEP A RELATIVELY TIGHT GRADIENT ACROSS THE REGION
THROUGH DEC 1 BEFORE A RELAXING GRADIENT ENDS THE THREAT. THIS SURFACE LOW
MOVING FROM THE BERING SEA INTO THE NORTH PACIFIC MAY ALSO BRING UNUSUALLY
HEAVY RAIN INTO SOUTHERN ALASKA AT THE SAME TIME, BUT THE PETS SHOW LESSER ODDS
FOR PRECIPITATION AMOUNTS TO REACH HAZARDS THRESHOLDS THAN FOR SUSTAINED WINDS,
SO NO PRECIPITATION THREAT IS POSTED AT THIS TIME.
FORECASTER: RICH TINKER
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