511
FXUS21 KWNC 182059
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 18 2024
SYNOPSIS: A SERIES OF MID-LEVEL LOWS FAVORS AN ACTIVE PATTERN FOR MUCH OF THE
CONTIGUOUS U.S. (CONUS) LEADING UP TO AND DURING THE THANKSGIVING HOLIDAY.
MID-LEVEL LOW PRESSURE ACROSS THE WEST AT THE ONSET OF THE PERIOD IS PREDICTED
TO BRING HEAVY PRECIPITATION TO PARTS OF NORTHERN CALIFORNIA IN ADDITION TO
HEAVY SNOW TO SOME HIGHER ELEVATION AREAS IN THE WEST COAST STATES, ROCKIES,
AND ADJACENT GREAT BASIN AREAS. THIS PATTERN IS ALSO CONDUCIVE TO PERIODS OF
HIGH WINDS ACROSS THE WEST COAST AND THE SOUTHWESTERN QUADRANT OF THE CONUS
FROM THE BEGINNING TO MIDDLE OF WEEK-2. ASSOCIATED SURFACE HIGH PRESSURE
INCREASES THE RISK FOR MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE
NORTH-CENTRAL CONUS. A FRONT AHEAD OF THIS MID-LEVEL LOW MAY ALSO LEAD TO HEAVY
PRECIPITATION ACROSS THE OHIO, TENNESSEE, AND LOWER MISSISSIPPI VALLEYS, AND
APPALACHIANS AT THE BEGINNING OF THE PERIOD. AS THIS MID-LEVEL LOW MOVES TO THE
CENTRAL CONUS DURING MID WEEK-2, THERE ARE INCREASED CHANCES FOR HEAVY SNOW
ACROSS NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, AND NORTHEAST,
AND HIGH WINDS FOR THE GREAT LAKES, NORTHEAST, AND CENTRAL APPALACHIANS DURING
MID WEEK-2.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PARTS OF NORTHERN CALIFORNIA,
TUE-THU, NOV 26-28.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE SIERRA NEVADA, KLAMATH
MOUNTAINS, CASCADE RANGE, AND HIGHER ELEVATIONS OF THE OLYMPIC PENINSULA,
TUE-THU, NOV 26-28.
SLIGHT RISK OF HEAVY SNOW ACROSS PARTS OF THE ROCKIES AND ADJACENT HIGH
ELEVATION AREAS OF THE GREAT BASIN, TUE-THU, NOV 26-28.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS MUCH OF THE WESTERN CONUS, TUE-SAT,
NOV 26-NOV 30.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY, TUE-MON, NOV 26-DEC 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE OHIO, TENNESSEE, AND LOWER
MISSISSIPPI VALLEYS, AND APPALACHIANS, TUE-THU, NOV 26-28.
SLIGHT RISK OF HEAVY SNOW ACROSS PARTS OF THE NORTHERN PLAINS, UPPER
MISSISSIPPI VALLEY, GREAT LAKES, AND NORTHEAST, THU-SAT, NOV 28-30.
SLIGHT RISK OF PERIODS OF HIGH WINDS ACROSS PARTS OF THE EAST COAST, GREAT
LAKES, NORTHEAST, AND CENTRAL APPALACHIANS, TUE-SAT, NOV 26-30.
POSSIBLE FLOOD ACROSS NORTHERN CALIFORNIA.
DETAILED SUMMARY
FOR THURSDAY NOVEMBER 21 - MONDAY NOVEMBER 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY NOVEMBER 26 - MONDAY DECEMBER 02: THERE IS RELATIVELY GOOD
AGREEMENT AMONG MULTIPLE MODEL ENSEMBLE MEANS INDICATING MID-LEVEL TROUGHING
PREDICTED ACROSS THE WESTERN CONUS AT THE ONSET OF WEEK-2, WHICH IS PREDICTED
TO INCREASE CHANCES FOR MULTIPLE HAZARDS ACROSS THE REGION DURING WEEK-2.
HOWEVER, BY DAY 9 (NOV 27), THERE ARE SIGNIFICANT DIFFERENCES AMONG MODEL
ENSEMBLE MEANS REGARDING THIS FEATURE, WITH THE GEFS FAVORING THE TROUGH AXIS
LOCATED OVER THE CENTRAL CONUS, THE ECENS HANGING FURTHER WEST ACROSS THE GREAT
BASIN, AND THE CMCE BEING MORE OF AN OUTLIER WITH MUCH WEAKER TROUGHING AND
LIMITED TO THE NORTH-CENTRAL TIER. THIS HIGH MODEL UNCERTAINTY TRANSLATES TO
INCREASED CONFIDENCE IN THE HAZARDS OUTLOOK TODAY. REGARDLESS OF THE DETAILS,
AN ACTIVE WEATHER PATTERN IS PREDICTED FOR WEEK-2 ACROSS MANY PARTS OF THE
CONUS DURING THE TRAVEL PERIOD LEADING UP TO AND DURING THE THANKSGIVING
HOLIDAY.
A SLIGHT RISK OF HEAVY PRECIPITATION IS DESIGNATED FOR PARTS OF NORTHERN
CALIFORNIA, NOV 26-28, WHERE THE GEFS, ECENS, AND CMCE PROBABILISTIC EXTREMES
TOOLS (PETS) INDICATE AT LEAST A 20% CHANCE OF 3-DAY PRECIPITATION TOTALS
EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY AND ONE INCH. ANTICIPATED HEAVY
PRECIPITATION DURING WEEKS-1 AND 2 AND ALREADY SATURATED SOILS SUPPORT
INCREASED CHANCES FOR FLOODING ACROSS NORTHERN CALIFORNIA, ALTHOUGH THERE IS
SOME UNCERTAINTY REGARDING THIS POTENTIAL ASSOCIATED WITH PRECIPITATION
DIFFERENCES ACROSS MODEL GUIDANCE. A SLIGHT RISK OF HEAVY SNOW IS DESIGNATED
FOR PORTIONS OF THE SIERRA NEVADA, KLAMATH MOUNTAINS, CASCADE RANGE, AND HIGHER
ELEVATIONS OF THE OLYMPIC PENINSULA, ROCKIES AND ADJACENT HIGH ELEVATION AREAS
OF THE GREAT BASIN FOR THE SAME PERIOD. THE GEFS PET INDICATES AT LEAST A 20%
CHANCE OF 3-DAY ACCUMULATED SNOW WATER EQUIVALENT TOTALS EXCEEDING THE 85TH
PERCENTILE AND HALF AN INCH, ONE INCH LOCALLY, IN THE HIGHLIGHTED RISK REGION.
SURFACE HIGH PRESSURE IS PREDICTED TO SINK SOUTHWARD FROM CENTRAL CANADA INTO
THE NORTH-CENTRAL CONUS FROM THE END OF WEEK-1 THROUGHOUT WEEK-2, SUPPORTING
INCREASED CHANCES FOR ANOMALOUS COLD ACROSS THE REGION. A SLIGHT RISK OF MUCH
BELOW NORMAL TEMPERATURES IS HIGHLIGHTED ACROSS THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY THROUGHOUT WEEK-2, WHERE THERE IS GOOD AGREEMENT IN THE PETS
OF MINIMUM TEMPERATURES HAVING AT LEAST A 20% CHANCE OF VALUES FALLING TO THE
LOWEST 15TH PERCENTILE AND BELOW ZERO DEG F. ENHANCED WINDS COULD ALSO SUPPORT
LOWER WIND CHILL TEMPERATURES IN THIS AREA. SURFACE LOWS ACROSS THE GREAT BASIN
ADJACENT TO SURFACE HIGH PRESSURE IS PREDICTED TO RESULT IN TIGHT PRESSURE
GRADIENTS SUPPORTING A BROAD AREA HIGHLIGHTED WITH A SLIGHT RISK OF EPISODIC
HIGH WINDS ACROSS MUCH OF THE WEST, NOV 26-30. PETS INDICATE AT LEAST A 20%
CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE ACROSS THE RISK AREA.
AS THE AFOREMENTIONED MID-LEVEL TROUGH SHIFTS FROM THE WESTERN CONUS TO THE
CENTRAL, ASSOCIATED SURFACE LOW PRESSURE IS PREDICTED TO TRACK FROM THE GREAT
PLAINS TO THE UPPER MIDWEST WITH A TRAILING FRONT EXTENDING SOUTHWARD
INCREASING CHANCES FOR HAZARDS ACROSS THE EASTERN HALF OF THE CONUS, ALTHOUGH
THERE ARE NOTABLE DIFFERENCES ACROSS MODEL GUIDANCE REGARDING THE DETAILS. A
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE OHIO, TENNESSEE, AND LOWER
MISSISSIPPI VALLEYS, AND APPALACHIANS, NOV 26-28. THERE IS GOOD CONSENSUS
ACROSS MULTIPLE MODEL PETS INDICATING AT LEAST A 20% CHANCE OF 3-DAY
PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE AND ONE INCH, FURTHER
SUPPORTED BY THE UNCALIBRATED ECENS. A SLIGHT RISK OF HEAVY SNOW IS POSTED FOR
NORTHERN PLAINS, UPPER MISSISSIPPI VALLEY, GREAT LAKES, AND NORTHEAST, NOV
28-30, PRIMARILY BASED ON THE UNCALIBRATED ECENS AND GENERAL ANTICIPATED TRACK
PATH OF SURFACE LOW PRESSURE. A SLIGHT RISK OF EPISODIC HIGH WINDS IS ALSO
POSTED FOR PARTS OF THE EAST COAST, GREAT LAKES, NORTHEAST, AND CENTRAL
APPALACHIANS, TUE-SAT, NOV 26-30, ASSOCIATED WITH AN INITIAL DEPARTING SURFACE
LOW OVER THE NORTHEAST AT THE BEGINNING OF WEEK-2 FOLLOWED BY A SECONDARY STORM
SYSTEM TRACKING TOWARDS THE GREAT LAKES BY THE MIDDLE OF THE PERIOD. THE ECENS
PET SHOWS AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE
AND 20 MPH ACROSS THE HIGHLIGHTED RISK AREA.
WEAK MID-LEVEL RIDGING IS FORECAST FOR ALASKA DURING WEEK-2, RESULTING IN
DECREASED CHANCES FOR WIDESPREAD HAZARDS. THUS, NO HAZARDS ARE DESIGNATED AT
THIS TIME FOR THE STATE.
FORECASTER: MELISSA OU
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