380
FXUS21 KWNC 111947
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 11 2024
SYNOPSIS: THERE IS SIGNIFICANTLY INCREASED UNCERTAINTY REGARDING POSSIBLE
MID-LEVEL LOW PRESSURE FORMING OVER THE NORTHEAST PACIFIC. IN GENERAL MODELS
DEPICT A WEAKER LOW AND LESS FAVORABLE ORIENTATION FOR HAZARDOUS IMPACTS TO THE
NORTHWESTERN CONTIGUOUS U.S. (CONUS) COMPARED TO YESTERDAY. GIVEN THESE
CHANGES, THE SLIGHT RISKS FOR HEAVY PRECIPITATION HAS BEEN DECREASED IN SPATIAL
AND TEMPORAL COVERAGE RELATIVE TO YESTERDAY’S OUTLOOK. A SLIGHT RISK FOR HIGH
WINDS IS MAINTAINED ACROSS THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, AND
THE MODERATE RISK IS REMOVED IN TODAY’S FORECAST. SURFACE LOWS AND ASSOCIATED
FRONTS TRACKING ACROSS THE NORTHERN PLAINS MAY SUPPORT EPISODIC HIGH WINDS. A
SERIES OF STORMS OVER THE GULF OF ALASKA COULD BRING HIGH WINDS TO COASTAL
PORTIONS OF SOUTH-CENTRAL AND 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, SAT-MON, DEC 21-23.
SLIGHT RISK OF PERIODIC HEAVY SNOW FOR HIGH ELEVATION PORTIONS OF THE CASCADES,
SAT-MON, DEC 21-23.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, THU-MON, DEC 19-23.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF THE NORTHERN AND CENTRAL
PLAINS, SAT-MON, DEC 21-23.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE SOUTHEAST
U.S., TENNESSEE VALLEY, AND LOWER MISSISSIPPI VALLEY, SUN-MON, DEC 22-23.
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS PARTS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, THU-MON, DEC 19-23.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, THU-MON, DEC 19-23.
DETAILED SUMMARY
FOR SATURDAY DECEMBER 14 - WEDNESDAY DECEMBER 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY DECEMBER 19 - WEDNESDAY DECEMBER 25: THERE IS SIGNIFICANTLY
INCREASED UNCERTAINTY AMONG MODELS REGARDING THE POTENTIAL FORMATION OF
AMPLIFIED MID-LEVEL TROUGHING OVER THE NORTHEASTERN PACIFIC DURING WEEK-2. IN
GENERAL MODELS’ DEPICTION OF THE AMPLITUDE AND ORIENTATION OF THIS FEATURE IS
LESS FAVORABLE TO IMPACTS ACROSS THE NORTHWESTERN CONUS COMPARED TO YESTERDAY.
THE GEFS AND INTEGRATED VAPOR TRANSPORT (IVT) TOOLS INDICATE ENHANCED IVT
VALUES (250 KG/M/S) LIMITED TO UPPER PORTIONS OF THE PACIFIC NORTHWEST AT THE
START OF THE PERIOD, WHEREAS THE ECENS COUNTERPART INDICATES A BROADER AREA
EXTENDING INTO NORTHERN CALIFORNIA. THESE DIFFERENCES TRANSLATE TO THE
PROBABILISTIC EXTREMES TOOLS (PETS) HAVING DECREASED SIGNALS OF PRECIPITATION
AND WINDS REACHING HAZARDOUS CRITERIA COMPARED TO YESTERDAY, TEMPORALLY AND
SPATIALLY. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS LIMITED TO
COASTAL PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, DEC 21-23,
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 PETS.
TODAY’S PETS INDICATE ONLY LOCALIZED AREAS EXPECTED TO RECEIVE 3-DAY
PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY AND 2
INCHES.
THERE IS NO MODERATE RISK OF HIGH WINDS DESIGNATED FOR TODAY DUE TO THE
DECREASING PROBABILITIES IN MODEL TOOLS OF WEATHER CONDITIONS REACHING
HAZARDOUS CRITERIA. A SLIGHT RISK IS CONTINUED FOR PORTIONS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, DEC 19-23, 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 WHICH 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 21-23, WHERE PETS SHOW AT LEAST A 20%
CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 20 MPH.
THERE IS MULTI-MODEL DEPICTION OF AMPLIFIED TROUGHING FORMING OVER THE EASTERN
CONUS TOWARDS THE MIDDLE OF 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 22-23, WHERE PETS INDICATE
AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES FALLING TO THE LOWEST 15TH
PERCENTILE AND SUB-FREEZING.
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
19-23, WHERE THE PETS INDICATE AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING
THE 85TH PERCENTILE AND 40 MPH. ENHANCED ONSHORE FLOW SUPPORTS A SLIGHT RISK OF
PERIODIC HEAVY PRECIPITATION AND HIGH WINDS ACROSS SOUTHEASTERN ALASKA, DEC 19
TO 23. 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 (ANOMALOUSLY WARM AT LOWER
ELEVATIONS) INCREASES THE RISK OF FLOODING AND LANDSLIDES FOR LOCALIZED AREAS.
FORECASTER: MELISSA OU
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