327
FXUS21 KWNC 131941
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 13 2024
SYNOPSIS: MULTIPLE MODELS INDICATE MORE AMPLIFIED MID-LEVEL LOW PRESSURE OVER
THE EAST COMPARED TO YESTERDAY, RESULTING IN INCREASED CHANCES FOR ASSOCIATED
IMPACTS. SLIGHT RISKS ARE HIGHLIGHTED IN TODAY’S OUTLOOK FOR MUCH BELOW NORMAL
TEMPERATURES FOR PARTS OF THE UPPER MISSISSIPPI VALLEY AND NORTHEAST, AS WELL
AS HEAVY LAKE EFFECT SNOW ACROSS THE GREAT LAKES. MODERATE AND SLIGHT RISKS OF
MUCH BELOW NORMAL TEMPERATURES ARE HIGHLIGHTED FOR THE SOUTHEASTERN CONTIGUOUS
U.S. AT THE BEGINNING OF THE PERIOD. THERE CONTINUES TO BE HIGH UNCERTAINTY
REGARDING THE DETAILS OF THE DEVELOPMENT OF A MID-LEVEL LOW OVER THE NORTHEAST
PACIFIC, THUS CONTINUING THE SUPPORT FOR SLIGHT RISKS FOR HEAVY PRECIPITATION
FOR COASTAL PORTIONS OF THE PACIFIC NORTHWEST, HIGH ELEVATION SNOW OVER THE
CASCADES, AND HIGH WINDS FOR THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA.
SURFACE LOWS AND ASSOCIATED FRONTS TRACKING ACROSS THE NORTHERN PLAINS MAY
SUPPORT EPISODIC HIGH WINDS ACROSS PARTS OF THE GREAT PLAINS. SURFACE HIGH
PRESSURE ANTICIPATED TO BUILD ACROSS THE GREAT BASIN WITH ADJACENT SURFACE LOW
PRESSURE ALONG THE SOUTHERN COAST OF CALIFORNIA MAY BE CONDUCIVE FOR EPISODIC
SANTA ANA WINDS. 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.
HAZARDS
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE
SOUTHEASTERN U.S. AND LOWER MISSISSIPPI VALLEY, SUN-MON, DEC 22-23.
MODERATE RISK OF EPISODIC HIGH WINDS ACROSS THE ALASKA PANHANDLE, SAT-MON, DEC
21-23.
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS COASTAL PARTS OF THE PACIFIC
NORTHWEST, 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, SAT-MON, DEC 21-23.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF THE NORTHERN AND CENTRAL
PLAINS, SAT-FRI, DEC 21-27.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE UPPER
MISSISSIPPI VALLEY AND NORTHEAST, SAT-MON, DEC 21-23.
SLIGHT RISK OF HEAVY LAKE EFFECT SNOW FOR PARTS OF THE GREAT LAKES, 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, SAT-TUE, DEC 21-24.
SLIGHT RISK OF EPISODIC HIGH WINDS ACROSS PARTS OF SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA, SAT-WED, DEC 21-25.
SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS PARTS OF THE ALASKA
PANHANDLE, SAT-WED, DEC 21-25.
DETAILED SUMMARY
FOR MONDAY DECEMBER 16 - FRIDAY DECEMBER 20:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY DECEMBER 21 - FRIDAY DECEMBER 27: MULTIPLE MODELS INDICATE
AMPLIFIED MID-LEVEL TROUGHING CONTINUING FROM THE END OF WEEK-1 INTO THE
WEEK-2. THE ECENS INTEGRATED VAPOR TRANSPORT (IVT) TOOLS SHOW SIGNIFICANTLY
HIGHER PROBABILITIES OF ENHANCED IVT VALUES (250 KG/M/S) FOR PRIMARILY THE
PACIFIC NORTHWEST COMPARED TO THE GEFS. A SLIGHT RISK OF HEAVY PRECIPITATION IS
CONTINUED FOR THIS REGION, 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 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 21-23, 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). MULTIPLE MODELS HAVE CONSISTENTLY INDICATED THE
POTENTIAL FOR SURFACE HIGH PRESSURE BUILDING OVER THE GREAT BASIN WITH THE
POTENTIAL FOR THE AXIS OF AN INVERTED SURFACE TROUGH FORMING OVER COASTAL
SOUTHWESTERN CALIFORNIA. THIS PATTERN SUPPORTS A SLIGHT RISK OF PERIODS OF
SANTA ANA WINDS ACROSS THE SOUTHWESTERN COAST OF CALIFORNIA THROUGHOUT WEEK-2.
IN GENERAL, HIGH WINDS ALONG THE WEST COAST WOULD INCREASE WILDFIRE RISK,
ESPECIALLY WHERE THERE ARE ALREADY ACTIVE WILDFIRES. THE NATIONAL INTERAGENCY
FIRE CENTER (NIFC) INDICATES INCREASED RISK FOR SIGNIFICANT FIRE POTENTIAL
ACROSS THIS REGION AT THE END OF WEEK-1.
A SERIES OF SURFACE LOWS AND ASSOCIATED FRONTS ARE FORECAST TO TRACK ACROSS THE
NORTHERN PLAINS THROUGHOUT MUCH 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 DURING THE PERIOD, WHERE PETS SHOW AT LEAST
A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH.
MULTIPLE MODEL ENSEMBLE MEANS SHOW A MORE AMPLIFIED TROUGH FORMING OVER THE
EASTERN CONUS DURING WEEK-2, COMPARED TO YESTERDAY. THIS TRANSLATES TO
INCREASING SIGNALS FOR ANOMALOUS COLD ACROSS THE REGION. SLIGHT RISKS (20-40%
CHANCE) OF MUCH BELOW NORMAL TEMPERATURE ARE HIGHLIGHTED IN TODAY’S OUTLOOK FOR
THE UPPER MISSISSIPPI VALLEY AND NORTHEAST, DEC 21-23. THE ECENS AND CMCE PETS
SHOW AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES FALLING TO THE LOWEST 15TH
PERCENTILE AND 0 DEG F, WITH RECENT DETERMINISTIC GUIDANCE INDICATING NEGATIVE
TEMPERATURE ANOMALIES REACHING AT LEAST 16 DEG F BELOW NORMAL. WITH GREAT LAKES
TEMPERATURES REMAINING RELATIVELY WARM AND ANTICIPATED COLD TEMPERATURES,
SLIGHT RISKS FOR HEAVY LAKE EFFECT SNOW ARE POSTED ACROSS PORTIONS OF THE GREAT
LAKES, DEC 21-23.
MULTIPLE PETS INDICATE AT LEAST A 40% CHANCE OF MINIMUM TEMPERATURES FALLING TO
THE LOWEST 15TH PERCENTILE AND SUB-FREEZING. THEREFORE, A MODERATE RISK OF MUCH
BELOW NORMAL TEMPERATURES IS POSTED FOR SOUTHEASTERN U.S. AND LOWER MISSISSIPPI
VALLEY, DEC 22-23. A BROADER AREA IS HIGHLIGHTED WITH A SLIGHT RISK OF MUCH
BELOW NORMAL TEMPERATURES ACROSS THE SOUTHEAST U.S., TENNESSEE VALLEY, AND
LOWER MISSISSIPPI VALLEY, DEC 21-24, WHERE PETS INDICATE AT LEAST A 20% CHANCE
OF THESE TEMPERATURE THRESHOLDS OCCURRING.
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
21-25, 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 PRIMARILY BASED ON RECENT DETERMINISTIC
MODEL GUIDANCE AND THE ECENS PET INCREASING PROBABILITIES ABOVE 40% FOR
REACHING THESE HAZARDOUS THRESHOLDS. ENHANCED ONSHORE FLOW FROM THESE STORMS
ALSO SUPPORTS A SLIGHT RISK OF PERIODIC HEAVY PRECIPITATION ACROSS SOUTHEASTERN
ALASKA, DEC 21-25. 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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