553
FXUS21 KWNC 241914
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 24 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FORECAST TO EXTEND FROM THE GULF OF ALASKA
SOUTHWARD TO THE WEST COAST AT THE BEGINNING OF DECEMBER. ENHANCED ONSHORE
FLOW, ASSOCIATED WITH THIS MID-LEVEL LOW PRESSURE, INCREASES THE RISK OF HEAVY
PRECIPITATION, HIGH WINDS, AND HEAVY SNOW FOR THE PACIFIC NORTHWEST,
INTERMOUNTAIN WEST, NORTHERN CALIFORNIA, AND SOUTHEASTERN ALASKA FROM DECEMBER
2 TO 5. AS MID-LEVEL LOW PRESSURE TRACKS EASTWARD FROM THE SOUTHWEST, THERE IS
AN INCREASED CHANCE OF HEAVY PRECIPITATION ACROSS EASTERN TEXAS, THE LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST FROM DECEMBER 2 TO 4. THE PREVAILING PACIFIC
FLOW IS LIKELY TO RESULT IN ABOVE-NORMAL TEMPERATURES FOR A MAJORITY OF THE
CONTIGUOUS U.S. (CONUS).
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, SAT-TUE, DEC 2-5.
SLIGHT RISK OF HEAVY SNOW FOR THE CASCADES, NORTHERN SIERRA NEVADA MOUNTAINS,
AND HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST, SAT-TUE, DEC 2-5.
SLIGHT RISK OF HEAVY SNOW FOR SOUTHWESTERN COLORADO, SAT-SUN, DEC 2-3.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST, SAT-TUE, DEC 2-5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR EASTERN TEXAS, THE LOWER MISSISSIPPI
VALLEY, AND PARTS OF THE SOUTHEAST, SAT-MON, DEC 2-4.
SLIGHT RISK OF HIGH WINDS FOR THE ALASKA PENINSULA, COASTAL SOUTHERN ALASKA,
AND SOUTHEASTERN ALASKA, SAT-TUE, DEC 2-5.
DETAILED SUMMARY
FOR MONDAY NOVEMBER 27 - FRIDAY DECEMBER 01:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY DECEMBER 02 - FRIDAY DECEMBER 08: THE 0Z GEFS, ECMWF, AND CANADIAN
ENSEMBLE MEANS DEPICT AN AMPLIFIED 500-HPA TROUGH OVER THE NORTHEASTERN PACIFIC
FROM DECEMBER 2 TO 5. THIS PREDICTED LONGWAVE PATTERN WOULD RESULT IN A WET
START TO DECEMBER WITH A SLIGHTLY ELEVATED RISK OF HAZARDOUS WEATHER ALONG THE
WEST COAST. THE GEFS AND ECMWF MODELS REMAIN CONSISTENT IN TIMING (DECEMBER
3-5) AND LOCATION (OREGON AND NORTHERN CALIFORNIA) OF ENHANCED PROBABILITIES
FOR INTEGRATED VAPOR TRANSPORT (IVT) VALUES TO EXCEED 250 KG/M/S. A SLIGHT RISK
OF HEAVY PRECIPITATION (DECEMBER 2-5) IS POSTED FOR NORTHERN CALIFORNIA AND THE
PACIFIC NORTHWEST WHERE THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS)
DEPICT 3-DAY PRECIPITATION AMOUNTS HAVING A 20 TO 40 PERCENT CHANCE OF
EXCEEDING THE 85TH PERCENTILE AND NEAR 2 INCHES, LIQUID EQUIVALENT. SINCE THE
GEFS AND ECMWF PETS HAVE LESS THAN A 40 PERCENT CHANCE OF 3-DAY PRECIPITATION
AMOUNTS EXCEEDING 2 INCHES AND THE EXPECTATION OF ANY HEAVY PRECIPITATION
LIKELY HAVING A SHORT DURATION, A MODERATE RISK OF HEAVY PRECIPITATION IS NOT
WARRANTED. IN ADDITION, WITH MOSTLY DRY WEATHER FORECAST DURING THE NEXT WEEK
AND 28-DAY STREAMFLOWS NEAR OR BELOW AVERAGE ACROSS NORTHERN CALIFORNIA,
OREGON, AND WASHINGTON, THE FLOODING RISK APPEARS LOW THROUGH EARLY DECEMBER.
BASED ON THE PREDICTED 500-HPA PATTERN ALONG WITH SUPPORT FROM THE GEFS SNOW
PET, A SLIGHT RISK OF HEAVY SNOW IS POSTED FOR THE CASCADES, NORTHERN SIERRA
NEVADA MOUNTAINS, AND HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST FROM DECEMBER
2-5. A SLIGHT RISK OF HEAVY SNOW IS ALSO POSTED FOR SOUTHWESTERN COLORADO ON
DECEMBER 2 AND 3 WHEN A SHORTWAVE TROUGH IS PREDICTED TO TRACK OVER THE FOUR
CORNERS REGION. THE AMPLIFIED TROUGH AND ENHANCED ONSHORE FLOW SUPPORT A BROAD
SLIGHT RISK OF HIGH WINDS ACROSS THE NORTHERN HALF OF THE WESTERN CONUS THROUGH
DECEMBER 5TH.
THE GEFS, ECMWF, AND CANADIAN ENSEMBLE MEANS FEATURE A SHORTWAVE TROUGH
EJECTING FROM THE SOUTHWEST AND MOST LIKELY TRACKING EASTWARD TO THE
SOUTH-CENTRAL CONUS ON DECEMBER 2 AND 3. BASED ON PRECIPITATION TOOLS AND
CONSISTENT WITH EL NIñO, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR
EASTERN TEXAS, THE LOWER MISSISSIPPI VALLEY, AND PARTS OF THE SOUTHEAST FROM
DECEMBER 2 TO 4. ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON NOVEMBER 21,
EXTREME (D3) TO EXCEPTIONAL (D4) DROUGHT IS DESIGNATED FOR 86.95 AND 89.69
PERCENT OF LOUISIANA AND MISSISSIPPI, RESPECTIVELY. THE PREDICTED WET PATTERN
DURING EARLY DECEMBER IS EXPECTED TO END FURTHER WORSENING OF THIS DROUGHT AND
COULD EVENTUALLY LEAD TO DROUGHT IMPROVEMENT.
A HIGH AMPLITUDE TROUGH IS LIKELY TO RESULT IN A DEEPENING LOW PRESSURE SYSTEM
OVER THE BERING SEA OR ALEUTIANS BY THE BEGINNING OF DECEMBER. THE GEFS AND
ECMWF ENSEMBLE MEMBERS DEPICT THIS LOW PRESSURE SYSTEM TRACKING SOUTHEASTWARD
TO THE GULF OF ALASKA EARLY IN WEEK-2. A MAJORITY OF THESE ENSEMBLE MEMBERS
FAVOR A MODERATELY STRONG LOW PRESSURE SYSTEM AND GIVEN THE PREDICTED TRACK, A
SLIGHT RISK OF HIGH WINDS IS POSTED FOR THE ALASKA PENINSULA, COASTAL SOUTHERN
ALASKA, AND SOUTHEASTERN ALASKA FROM DECEMBER 2 TO 5. LANDSLIDES HAVE BEEN
RECENTLY REPORTED IN THE ALASKA PANHANDLE AND HIGH WINDS COMBINED WITH
SATURATED SOILS MAINTAINS AN INCREASED THREAT FOR ADDITIONAL LANDSLIDES.
ALTHOUGH ABOVE-NORMAL PRECIPITATION IS FAVORED FOR SOUTHEASTERN ALASKA DURING
WEEK-2, PRECIPITATION AMOUNTS ARE LIKELY TO REMAIN BELOW HAZARDOUS CRITERIA. A
RECENT AERIAL FREEZE-UP SURVEY FOUND OPEN WATER AND THIN ICE ALONG THE
KUSKOKWIM RIVER WHICH MAKES RIVER TRAVEL HAZARDOUS.
FORECASTER: BRAD PUGH
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