954
FXUS21 KWNC 231846
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 23 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FORECAST TO EXTEND FROM THE GULF OF ALASKA
SOUTHWARD TO THE WEST COAST. ENHANCED ONSHORE FLOW, ASSOCIATED WITH THIS
MID-LEVEL LOW PRESSURE, INCREASES THE RISK OF HEAVY PRECIPITATION, HIGH WINDS,
AND HEAVY SNOW FOR PARTS OF THE WEST AND ALASKA. DURING EARLY DECEMBER,
ABOVE-NORMAL PRECIPITATION IS FAVORED FOR DROUGHT-STRICKEN AREAS OF THE SOUTH.
FOLLOWING A PERIOD OF ANOMALOUSLY COLD TEMPERATURES ACROSS THE CENTRAL AND
EASTERN CONTIGUOUS U.S. (CONUS) DURING THE FINAL WEEK OF NOVEMBER, THE
PREVAILING PACIFIC FLOW IS LIKELY TO RESULT IN NEAR OR ABOVE-NORMAL
TEMPERATURES THROUGHOUT THE CONUS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, SAT-THU, DEC 2-7.
SLIGHT RISK OF HEAVY SNOW FOR THE CASCADES, NORTHERN SIERRA NEVADA MOUNTAINS,
AND HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST, SAT-THU, DEC 2-7.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST, SAT-THU, DEC 2-7.
SLIGHT RISK OF HEAVY PRECIPITATION FOR EASTERN TEXAS, THE LOWER MISSISSIPPI
VALLEY, AND TENNESSEE VALLEY, FRI-MON, DEC 1-4.
SLIGHT RISK OF HIGH WINDS FOR THE ALASKA PENINSULA, COASTAL SOUTHERN ALASKA,
AND SOUTHEASTERN ALASKA, FRI-TUE, DEC 1-5.
DETAILED SUMMARY
FOR SUNDAY NOVEMBER 26 - THURSDAY NOVEMBER 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY DECEMBER 01 - THURSDAY DECEMBER 07: THE 0Z GEFS AND ECMWF ENSEMBLE
MEANS DEPICT A STRENGTHENING 500-HPA TROUGH OVER THE NORTHEASTERN PACIFIC
DURING WEEK-2. HOWEVER, THE 0Z CANADIAN ENSEMBLE MEAN FEATURES A MORE
PROGRESSIVE TROUGH INTO THE INTERIOR WESTERN CONUS. THE 0Z GEFS AND ECMWF
ENSEMBLE MEANS ARE THE FAVORED MODEL SOLUTIONS DUE TO THEIR GOOD AGREEMENT AND
CONSISTENCY. 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 ECMWF MODEL REMAINS CONSISTENT IN TIMING (DECEMBER 4 AND 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 2-7) 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 DEPICT LESS THAN A 40 PERCENT CHANCE OF 3-DAY PRECIPITATION
AMOUNTS TO EXCEED 2 INCHES, A MODERATE RISK OF HEAVY PRECIPITATION IS NOT
WARRANTED AT THIS TIME. IN ADDITION, WITH MOSTLY DRY WEATHER FORECAST DURING
THE NEXT WEEK AND 28-DAY STREAMFLOWS NEAR AVERAGE, THE FLOODING RISK APPEARS
LOW THROUGH EARLY DECEMBER.
THE AMPLIFIED TROUGH AND ENHANCED ONSHORE FLOW SUPPORT A BROAD SLIGHT RISK OF
HIGH WINDS ACROSS THE WESTERN CONUS. BASED ON THE PREDICTED 500-HPA PATTERN
ALONG WITH 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. IF THE 500-HPA TROUGH AXIS REMAINS MORE OFFSHORE OF THE
WEST COAST, THEN SNOW LEVELS ARE LIKELY TO BE HIGHER. THE WIND AND SNOW HAZARDS
ARE VALID FROM DEC 2 TO 7.
EARLY IN WEEK-2, 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. 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 TENNESSEE VALLEY FROM DECEMBER 1 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 1 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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