239
FXUS21 KWNC 121916
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 12 2024
SYNOPSIS: THERE CONTINUES TO BE HIGH UNCERTAINTY REGARDING THE DETAILS OF THE
DEVELOPMENT OF A MID-LEVEL LOW OVER THE NORTHEAST PACIFIC TRANSLATING TO
UNCERTAINTY IN THE IMPACTS, ESPECIALLY FOR PRECIPITATION. SLIGHT RISKS FOR
HEAVY PRECIPITATION AND HIGH WINDS ARE HIGHLIGHTED ACROSS PARTS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA AT THE BEGINNING OF THE PERIOD, IN ADDITION
TO HIGH ELEVATION SNOW OVER THE CASCADES. SURFACE LOWS AND ASSOCIATED FRONTS
TRACKING ACROSS THE NORTHERN PLAINS MAY SUPPORT EPISODIC HIGH WINDS ACROSS
PARTS OF THE GREAT PLAINS. A SERIES OF STORMS OVER THE GULF OF ALASKA COULD
BRING HIGH WINDS AND HEAVY PRECIPITATION TO COASTAL PORTIONS OF SOUTHEASTERN
ALASKA DURING WEEK-2. POTENTIAL AMPLIFIED TROUGHING ACROSS THE EAST INCREASES
THE RISK FOR MUCH BELOW NORMAL TEMPERATURES ACROSS THE SOUTHEASTERN CONUS.
HAZARDS
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS COASTAL PARTS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, FRI-SUN, DEC 20-22.
SLIGHT RISK OF PERIODIC HEAVY SNOW FOR HIGH ELEVATION PORTIONS OF THE CASCADES,
FRI-SUN, DEC 20-22.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, FRI-SUN, DEC 20-22.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF THE NORTHERN AND CENTRAL
PLAINS, FRI-SUN, DEC 20-22.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE SOUTHEAST
U.S., TENNESSEE VALLEY, AND LOWER MISSISSIPPI VALLEY, SAT-TUE, DEC 21-24.
MODERATE RISK OF EPISODIC HIGH WINDS ACROSS THE ALASKA PANHANDLE, FRI-SUN, DEC
20-22.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, FRI-TUE, DEC 20-24.
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS PARTS OF THE ALASKA
PANHANDLE, FRI-TUE, DEC 20-24.
DETAILED SUMMARY
FOR SUNDAY DECEMBER 15 - THURSDAY DECEMBER 19:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY DECEMBER 20 - THURSDAY DECEMBER 26: MULTIPLE MODELS INDICATE
AMPLIFIED MID-LEVEL TROUGHING CONTINUING FROM THE END OF WEEK-1 INTO THE
WEEK-2. THE GEFS AND INTEGRATED VAPOR TRANSPORT (IVT) TOOLS INDICATE ENHANCED
IVT VALUES (250 KG/M/S) FOR THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA
ALTHOUGH WITH SOME DIFFERENCES IN DURATION AND SPATIAL EXTENT. A SLIGHT RISK OF
HEAVY PRECIPITATION IS CONTINUED FOR THIS REGION, DEC 20-22, WITH A SLIGHT RISK
OF HEAVY SNOW DESIGNATED ONLY FOR THE CASCADES FOR THE SAME PERIOD. THESE
HAZARDS ARE HIGHLIGHTED BASED ON UNCALIBRATED GUIDANCE AND WHERE THE ECENS AND
CANADIAN PROBABILISTIC EXTREMES TOOLS (PETS) SHOW AT LEAST A 20% CHANCE OF
3-DAY LIQUID EQUIVALENT TOTALS EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY
AND 2 INCHES. PROBABILITIES DECREASE FOR HEAVY PRECIPITATION THEREAFTER
ASSOCIATED WITH THE ANTICIPATION OF THE TROUGH RETROGRADING.
A SLIGHT RISK OF HIGH WINDS IS MAINTAINED, DEC 20-22, FOR PORTIONS OF THE
PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, WHERE PETS SHOW AT LEAST A 20%
CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 40 MPH (LOWER SPEEDS
ANTICIPATED FURTHER INLAND). ACROSS THE WEST, MULTIPLE MODELS INDICATE THE
POTENTIAL FOR SURFACE HIGH PRESSURE BUILDING OVER THE GREAT BASIN WITH THE
POTENTIAL FOR AN INVERTED SURFACE TROUGH OVER COASTAL SOUTHWESTERN CALIFORNIA.
THIS PATTERN IS CONDUCIVE FOR INCREASED CHANCES OF PERIODS OF SANTA ANA WINDS
ACROSS THE SOUTHWESTERN COAST OF CALIFORNIA. IN GENERAL, HIGH WINDS ALONG THE
WEST COAST WOULD INCREASE WILDFIRE RISK, ESPECIALLY WHERE THERE ARE ALREADY
ACTIVE WILDFIRES.
A SERIES OF SURFACE LOWS AND ASSOCIATED FRONTS ARE FORECAST TO TRACK ACROSS THE
NORTHERN PLAINS BY THE MIDDLE OF WEEK-2. COMBINED WITH ADJACENT SURFACE HIGH
PRESSURE OVER THE GREAT BASIN, THERE IS INCREASED POTENTIAL FOR TIGHT PRESSURE
GRADIENTS SUPPORTING HIGH WINDS. A SLIGHT RISK OF EPISODIC HIGH WINDS IS POSTED
FOR THE NORTHERN AND CENTRAL PLAINS, DEC 20-22, WHERE PETS SHOW AT LEAST A 20%
CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH.
THERE IS RELATIVELY GOOD AGREEMENT AMONG MODELS INDICATING AMPLIFIED TROUGHING
FORMING OVER THE EASTERN CONUS DURING WEEK-2. THIS PATTERN FAVORS SURFACE HIGH
PRESSURE BUILDING ACROSS THE EAST, BRINGING COLDER ARCTIC AIR SOUTHWARD. A
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS DESIGNATED FOR THE SOUTHEAST
U.S., TENNESSEE VALLEY, AND LOWER MISSISSIPPI VALLEY, DEC 21-24, WHERE PETS
INDICATE AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES FALLING TO THE LOWEST
15TH PERCENTILE AND SUB-FREEZING. THE GEFS PET HAS INCREASED SIGNALS FOR THESE
THRESHOLDS COMPARED TO YESTERDAY, COMING INTO BETTER AGREEMENT WITH THE ECENS
COUNTERPART.
THE MID-LEVEL TROUGH IN THE NORTHEAST PACIFIC MAY SUPPORT MULTIPLE STORMS
FORMING OVER THE GULF OF ALASKA. A SLIGHT RISK OF EPISODIC HIGH WINDS IS
MAINTAINED FOR COASTAL PORTIONS OF SOUTH-CENTRAL AND SOUTHEASTERN ALASKA, DEC
20-24, WHERE THE PETS INDICATE AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING
THE 85TH PERCENTILE AND 40 MPH. A MODERATE RISK OF HIGH WINDS IS DESIGNATED
ACROSS THE PANHANDLE AREA OF ALASKA, GIVEN INCREASED WIND SPEEDS SHOWING UP IN
RECENT DETERMINISTIC MODEL GUIDANCE AND THE ECENS PET INCREASING PROBABILITIES
ABOVE 40% FOR REACHING THESE HAZARDOUS THRESHOLDS. ENHANCED ONSHORE FLOW FROM
THESE STORMS SUPPORTS A SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION AND HIGH
WINDS ACROSS SOUTHEASTERN ALASKA, DEC 20-24. PETS INDICATE AT LEAST A 20%
CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND 2 INCHES. WHILE
THIS IS SOMEWHAT LOWER THAN TYPICALLY USED HAZARDS CRITERIA, THIS ENHANCED
PRECIPITATION POTENTIAL COMBINED WITH HIGH WINDS AND EXPECTED HIGH ELEVATION
FREEZING LEVELS INCREASES THE RISK OF FLOODING AND LANDSLIDES FOR LOCALIZED
AREAS. ANOMALOUSLY WARM TEMPERATURES ARE PREDICTED FOR THE ENTIRE STATE DURING
WEEK-2, WHICH CAN LEAD TO LOCALLY UNSAFE RIVER CONDITIONS THAT CAN IMPACT
TRAVEL AND SUBSISTENCE ACTIVITIES. MULTIPLE PETS INDICATE AT LEAST A 30% CHANCE
OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE, WITH ABOVE FREEZING
TEMPERATURES ANTICIPATED FOR SOUTHWESTERN AND SOUTHERN PORTIONS OF ALASKA AT
THE BEGINNING OF WEEK-2.
FORECASTER: MELISSA OU
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