610
FXUS21 KWNC 142100
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 14 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FAVORED ACROSS THE WEST COAST OF THE
CONTIGUOUS U.S. (CONUS) THROUGHOUT THE FORECAST PERIOD, RESULTING IN THE
POTENTIAL FOR HEAVY PRECIPITATION AND HIGH WINDS ALONG THE COAST, AS WELL AS
HEAVY SNOW FOR HIGHER ELEVATIONS IN THE INTERIOR WEST. A CUT-OFF LOW PRESSURE
SYSTEM IS FAVORED TO BREAK AWAY FROM THE MAIN TROUGH AXIS EARLY IN THE PERIOD
AND MOVE ACROSS THE SOUTHERN CONUS, BRINGING A RISK FOR HEAVY PRECIPITATION
FROM THE FOUR CORNERS TO THE LOWER MISSISSIPPI VALLEY. A SERIES OF SURFACE LOW
PRESSURE SYSTEMS ARE PREDICTED TO MOVE FROM THE BERING SEA INTO THE GULF OF
ALASKA DURING THE FORECAST PERIOD, RESULTING IN A STORMY FORECAST WITH THE
POTENTIAL FOR HIGH WINDS AND HEAVY PRECIPITATION FOR MUCH OF THE SOUTHERN COAST
OF ALASKA.
HAZARDS
MODERATE RISK FOR HEAVY PRECIPITATION FOR COASTAL PORTIONS OF CALIFORNIA SOUTH
OF SAN FRANCISCO, MON-THU, DEC 25-28.
MODERATE RISK FOR HEAVY PRECIPITATION FOR MUCH OF CENTRAL AND WESTERN ARIZONA
AND ADJACENT PORTIONS OF CALIFORNIA AND NEVADA, FRI-SAT, DEC 22-23.
MODERATE RISK FOR HEAVY SNOW FOR THE CENTRAL SIERRA NEVADA MOUNTAINS, MON-THU,
DEC 25-28.
MODERATE RISK FOR HEAVY SNOW FOR THE WASATCH MOUNTAINS, FRI-SUN, DEC 22-24.
MODERATE RISK FOR HEAVY SNOW FOR THE HIGHER ELEVATIONS OF COLORADO, FRI-MON,
DEC 22-25.
MODERATE RISK FOR HIGH WINDS FOR PORTIONS OF THE CALIFORNIA AND OREGON COASTS,
MON-THU, DEC 25-28.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF SOUTHWEST OREGON AND MUCH
OF CALIFORNIA, SUN-THU DEC 24-28.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST U.S., SAT-MON, DEC 23-25.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR MUCH OF ARIZONA AND NEW MEXICO,
FRI-SUN, DEC 22-24
SLIGHT RISK FOR HEAVY PRECIPITATION FOR COASTAL PORTIONS OF ALASKA FROM PRINCE
WILLIAMS SOUND SOUTH TO INCLUDE ALL OF THE ALASKAN PANHANDLE, FRI-MON, DEC.
22-25.
SLIGHT RISK FOR HEAVY SNOW FOR THE SIERRA NEVADAS AND COASTAL MOUNTAINS OF
NORTHERN CALIFORNIA AND SOUTHERN OREGON, MON-THU DEC 25-28.
SLIGHT RISK FOR HEAVY SNOW FOR THE CENTRAL ROCKIES AND WASATCH MOUNTAINS AS
WELL AS PORTIONS OF WESTERN AND SOUTHERN WYOMING, FRI-MON, DEC 22-25.
SLIGHT RISK FOR HIGH WINDS FOR COASTAL PORTIONS OF CALIFORNIA, OREGON, AND
WASHINGTON, SUN-THU, DEC 24-28.
SLIGHT RISK FOR HIGH WINDS FOR COASTAL PORTIONS OF ALASKA FROM NUNIVAK ISLAND
SOUTH AND EAST TO INCLUDE ALL OF THE ALASKAN PENINSULA, KODIAK ISLAND, THE
KENAI PENINSULA, AND THE ALASKA PANHANDLE, FRI-MON, DEC. 22-25.
DETAILED SUMMARY
FOR SUNDAY DECEMBER 17 - THURSDAY DECEMBER 21:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY DECEMBER 22 - THURSDAY DECEMBER 28: AFTER SEVERAL DAYS WITH
SIGNIFICANT UNCERTAINTY AND DIFFERING SOLUTIONS FROM MODEL ENSEMBLES, THE GEFS
HAS COME ON BOARD WITH THE ECMWF FAVORING A CUT-OFF LOW OFF THE COAST OF
SOUTHERN CALIFORNIA AT THE OUTSET OF WEEK-2. THE END OF THE FORECAST PERIOD HAS
ENSEMBLE SOLUTIONS CONTINUING TO DEPICT A RELOADING OF THE MID-LEVEL TROUGH OFF
THE WEST COAST AND A FRESH WAVE OF STORMY ONSHORE FLOW FOR CALIFORNIA DURING
THE SECOND HALF OF WEEK-2. AS FOR THE INITIAL WAVE, MODELS INDICATE THE
POTENTIAL FOR HEAVY PRECIPITATION FOR MUCH OF ARIZONA AS WELL AS PORTIONS OF
THE SOUTHERN AND SOUTHEAST CONUS, AND HEAVY SNOW IN THE MOUNTAINS OF THE
INTERIOR WEST IN THE DAYS LEADING UP TO CHRISTMAS.
AS THE CUT-OFF LOW MOVES ASHORE AT THE OUTSET OF WEEK-2, THE POTENTIAL FOR
HEAVY PRECIPITATION MOVES WITH IT FROM WEST TO EAST, BEGINNING IN THE DESERT
SOUTHWEST AND MOVING ACROSS THE SOUTHERN PLAINS TOWARDS THE SOUTHEAST U.S. THIS
IS SUPPORTED BY THE ECMWF AND GEFS PROBABILISTIC EXTREMES TOOLS (PETS), WHICH
BOTH INDICATE AT LEAST A 20% PROBABILITY OF 3-DAY PRECIPITATION TOTALS
EXCEEDING THE 85TH PERCENTILE AND AT LEAST A HALF INCH FOR PORTIONS OF THE
DESERT SOUTHWEST DURING DEC 22-24, AND ABOVE 40% PROBABILITIES FOR MUCH OF
ARIZONA EARLY IN WEEK-2. AS THIS SYSTEM MOVES INTO THE PLAINS, THE PETS
INDICATE A 20% PROBABILITY FOR 3-DAY PRECIPITATION TOTALS TO EXCEED 1 INCH.
CONSISTENT WITH THIS GUIDANCE, A MODERATE RISK FOR HEAVY PRECIPITATION IS
POSTED FOR MUCH OF ARIZONA FOR DEC 22-23, A SLIGHT RISK FOR HEAVY PRECIPITATION
COVERS THE ABOVE AREA ALONG WITH AN EASTWARD EXTENSION INTO PORTIONS OF NEW
MEXICO AND WEST TEXAS FOR DEC 22-24, AND A SLIGHT RISK FOR HEAVY PRECIPITATION
COVERING PORTIONS OF THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND
SOUTHEAST U.S. FOR DEC 23-25. MODELS ALSO DEPICT WIDESPREAD SNOW IN THE HIGHER
ELEVATIONS. THIS IS WELL-INDICATED BY THE GEFS SNOW WATER EQUIVALENT (SWE) PET,
WHICH HAS WIDESPREAD PROBABILITIES ABOVE 20% FOR EXCEEDING THE 85TH PERCENTILE
AND AT LEAST A HALF INCH OF 3-DAY SWE, WITH OVER AN INCH POSSIBLE FOR THE
HIGHER ELEVATIONS. THEREFORE A SLIGHT RISK FOR HEAVY SNOW IS POSTED FOR THE
CENTRAL ROCKIES AND WASATCH MOUNTAINS AS WELL AS PORTIONS OF WESTERN AND
SOUTHERN WYOMING FOR DEC 22-25, A MODERATE RISK FOR THE WASATCH FOR DEC 22-24,
AND A MODERATE RISK FOR THE HIGHER ELEVATIONS OF COLORADO FOR DEC 22-25.
THERE IS CONTINUED CONFIDENCE REGARDING ENHANCED CHANCES FOR PERIODS OF HIGH
WINDS AND HEAVY PRECIPITATION FOR SOUTHWESTERN OREGON AND MUCH OF CALIFORNIA
DURING THE SECOND HALF OF THE FORECAST PERIOD. THE ECMWF REMAINS MORE BULLISH
THAN THE GEFS WITH THE CHANCES FOR HEAVY PRECIPITATION, ALTHOUGH THE GEFS HAS
INCREASED PROBABILITIES QUITE A BIT RELATIVE TO YESTERDAY. AN INITIAL WAVE
ASSOCIATED WITH THE CUT-OFF LOW IS FAVORED TO HAVE MOVED OFF THE COAST BY THE
BEGINNING OF WEEK-2 WITH MOST OF THE ACTIVITY NOW IN THE WEEK-1 TIME FRAME,
AFTER WHICH BOTH MODELS INDICATE A LULL IN STORMINESS UNTIL THE 24TH. AS THE
MID-LEVEL TROUGH RELOADS AND ONSHORE FLOW INCREASES, PROBABILITIES FOR HEAVY
PRECIPITATION AGAIN INCREASE. THE ECMWF PET INDICATES OVER A 60% PROBABILITY OF
3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND AT LEAST 1 INCH FOR
CENTRAL AND SOUTHERN CALIFORNIA DURING THIS PERIOD. THE GEFS PET KEEPS THE
PROBABILITIES MUCH LOWER BUT DOES APPROACH 40%. THEREFORE A MODERATE RISK FOR
HEAVY PRECIPITATION IS POSTED FOR COASTAL PORTIONS OF CALIFORNIA SOUTH OF SAN
FRANCISCO FOR DEC 25-28, WHERE THE PETS HAVE THE CLOSEST AGREEMENT, AND A
SLIGHT RISK IS POSTED FOR MUCH OF THE REMAINDER OF CALIFORNIA AND SOUTHWEST
OREGON FOR DEC 24-28. THE SIERRA NEVADA MOUNTAINS AS WELL AS COASTAL RANGES OF
NORTHERN CALIFORNIA AND SOUTHERN OREGON HAVE A SLIGHT RISK OF HEAVY SNOW POSTED
FOR 25-28 AND THE CENTRAL SIERRA NEVADAS HAVE A MODERATE RISK FOR HEAVY SNOW
POSTED FOR THE SAME DATES, FOLLOWING THE FORECAST REASONING OUTLINED ABOVE FOR
HEAVY PRECIPITATION. THE PETS FROM THE GEFS AND ECMWF ALSO INDICATE THE
POTENTIAL FOR HIGH WINDS ALONG THE WEST COAST SIMILAR TO WHAT IS SEEN WITH
HEAVY PRECIPITATION. BOTH MODELS INDICATE AT LEAST A 20% PROBABILITY OF WIND
SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH FOR THE ENTIRE WEST COAST, WITH
THE POTENTIAL FOR WIND SPEEDS TO EXCEED 40MPH FOR PORTIONS OF THE CALIFORNIA
AND OREGON COASTS. THEREFORE A MODERATE RISK FOR HIGH WINDS IS POSTED FROM COOS
BAY, OREGON TO POINT ARENA, CALIFORNIA FOR DEC 25-28, AND A SLIGHT RISK IS
POSTED FOR THE ENTIRE WEST COAST FOR DEC 24-28.
ENSEMBLE SOLUTIONS FROM THE GEFS, ECMWF, AND CMCE ALL INDICATE A SERIES OF DEEP
LOW PRESSURE SYSTEMS MOVING FROM THE BERING SEA INTO THE GULF OF ALASKA
THROUGHOUT THE WEEK-2 PERIOD, RESULTING IN ELEVATED CHANCES FOR HIGH WIND AND
HEAVY PRECIPITATION. PETS FROM ALL THREE MODELS INDICATE AT LEAST A 20%
PROBABILITY OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND AT LEAST 40 MPH
ALONG THE COAST FROM NUNIVAK ISLAND SOUTH, AND A 20% PROBABILITY OF 3-DAY
PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE ROUGHLY FROM PRINCE WILLIAM
SOUND SOUTH FOR MOST OF THE FORECAST PERIOD. DAILY ANALYSIS FROM THE MODEL
ENSEMBLES SUGGESTS THAT THE STRONGEST WINDS AND PRECIPITATION SHOULD EASE
TOWARDS THE END OF WEEK-2, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION AND
HIGH WINDS IS POSTED FOR DEC 22-25 FOR THE AREAS NOTED ABOVE.
FORECASTER: DANNY BARANDIARAN
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