419
FXUS21 KWNC 251922
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 25 2024
SYNOPSIS: FOLLOWING ABOVE-NORMAL TEMPERATURES ACROSS THE CENTRAL AND EASTERN
U.S TO END 2024, A PATTERN CHANGE IS FORECAST DURING EARLY JANUARY WITH A
TRANSITION TO NEAR OR BELOW-NORMAL TEMPERATURES. FROM JANUARY 5 TO 8, ARCTIC
HIGH PRESSURE IS EXPECTED TO SHIFT SOUTH FROM CANADA AND MAY BRING THE COLDEST
TEMPERATURES SO FAR THIS WINTER TO THE GREAT PLAINS AND MIDWEST. THERE IS AN
INCREASING RISK OF A WINTER STORM ACROSS THE CENTRAL AND EASTERN U.S. DURING
EARLY TO MID-JANUARY.
HAZARDS
SLIGHT RISK OF HEAVY HEAVY SNOW FOR THE INTERIOR NORTHEAST AND DOWNWIND OF
LAKES ERIE AND ONTARIO, THU, JAN 2.
SLIGHT RISK OF HIGH WINDS FOR THE NORTHEAST AND MID-ATLANTIC, THU, JAN 2.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE PACIFIC NORTHWEST,
THU-FRI, JAN 2-3.
SLIGHT RISK OF HEAVY SNOW FOR HIGH ELEVATIONS OF THE CASCADES, THU-FRI, JAN 2-3.
SLIGHT RISK OF HEAVY SNOW FOR MUCH OF THE ROCKIES, THU-SUN, JAN 2-5.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE CENTRAL U.S., SAT-MON, JAN 4-6.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR NORTH-CENTRAL FLORIDA,
SAT-SUN, JAN 4-5.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE NORTHERN GREAT PLAINS AND
NORTHWESTERN MINNESOTA, SUN-WED, JAN 5-8.
DETAILED SUMMARY
FOR SATURDAY DECEMBER 28 - WEDNESDAY JANUARY 01:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JANUARY 02 - WEDNESDAY JANUARY 08: ON JANUARY 2ND, A STRONG LOW
PRESSURE SYSTEM IS FORECAST TO BE CENTERED OVER NEW ENGLAND OR SOUTHEASTERN
CANADA. ON THE BACKSIDE OF THIS LOW PRESSURE SYSTEM, A SLIGHT RISK OF HEAVY
SNOW IS POSTED FOR PORTIONS OF NEW ENGLAND SOUTHWARD TO WESTERN NEW YORK AND
NORTHWESTERN PENNSYLVANIA. SNOWFALL AMOUNTS MAY BE ENHANCED BY LAKE-EFFECT
DOWNWIND OF LAKES ERIE AND ONTARIO. A SLIGHT RISK OF HIGH WINDS IS POSTED FOR
THE NORTHEAST AND MID-ATLANTIC GIVEN THE PREDICTED STRENGTH OF THE LOW PRESSURE
SYSTEM. THESE SNOW AND WIND HAZARDS ARE EXPECTED TO TIME OFF BY JANUARY 3RD.
FROM JANUARY 2ND TO THE 3RD, A SHORTWAVE TROUGH AND ENHANCED ONSHORE FLOW
SUPPORT A SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE PACIFIC NORTHWEST WITH
A SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE CASCADES. BASED ON
THE LATEST MODEL SOLUTIONS, THIS APPEARS TO BE A SHORT-LIVED PERIOD OF STORMY
WEATHER WITH A BUILDING RIDGE NEAR THE WEST COAST DURING THE REMAINDER OF
WEEK-2.
A SHORTWAVE TROUGH IS FORECAST TO SHIFT EASTWARD AND AMPLIFY OVER THE ROCKIES.
THIS AMPLIFYING SHORTWAVE TROUGH ALONG WITH UPSLOPE FLOW INCREASES THE CHANCE
OF HEAVY SNOW FROM THE NORTHERN INTERMOUNTAIN WEST SOUTH THROUGH THE CENTRAL
AND SOUTHERN ROCKIES. THE SLIGHT RISK OF HEAVY SNOW GENERALLY FOLLOWED THE GEFS
PROBABILISTIC EXTREMES TOOL (PET) WHERE IT DEPICTS A 20 PERCENT CHANCE OF
SNOWFALL AMOUNTS EXCEEDING THE 85TH PERCENTILE AND A LIQUID EQUIVALENT AT OR
ABOVE 0.5 INCH. THE SHORTWAVE TROUGH IS EXPECTED TO RESULT IN THE DEVELOPMENT
OF ONE OR TWO SURFACE LOWS ACROSS THE HIGH PLAINS LATER IN WEEK-2. BASED ON THE
GEFS PET SNOW TOOL, ENSEMBLE LOW TRACKS, AND 24-HOURS PRECIPITATION AMOUNTS
FROM THE GEFS AND ECMWF ENSEMBLE MEANS, A SLIGHT RISK OF HEAVY SNOW (JANUARY
4-6) EXTENDS FROM THE DAKOTAS SOUTH TO THE OKLAHOMA PANHANDLE AND EAST TO DES
MOINES AND KANSAS CITY. A LARGE SPATIAL EXTENT IS NECESSARY DUE TO THE LARGE
ENSEMBLE SPREAD AND POTENTIAL FOR A PAIR OF LOW PRESSURE SYSTEMS.
TO THE EAST OF THE MISSISSIPPI RIVER, FORECAST CONFIDENCE IS TOO LOW TO
DESIGNATE A HEAVY SNOW HAZARD AT THIS TIME. HOWEVER, THE LONGWAVE PATTERN WOULD
SUPPORT AN ELEVATED RISK OF A WINTER STORM FROM THE MIDWEST EAST TO THE
MID-ATLANTIC AND NORTHEAST. IF MODEL AGREEMENT IMPROVES THE NEXT DAY OR TWO,
THEN A HEAVY SNOW HAZARD MAY BE NECESSARY FOR THESE AREAS.
ON JANUARY 4-5, THE ECMWF ENSEMBLE MEAN DEPICTS SURFACE HIGH PRESSURE BECOMING
CENTERED OVER THE SOUTHEAST WHICH COULD LEAD TO SUBFREEZING TEMPERATURES FOR
NORTH-CENTRAL FLORIDA. A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS
POSTED FOR PORTIONS OF FLORIDA WHERE THE ECMWF PET DEPICTS MINIMUM TEMPERATURES
HAVING MORE THAN A 20 PERCENT CHANCE OF FALLING BELOW FREEZING.
HIGH LATITUDE BLOCKING WITH A PREDICTED NEGATIVE ARCTIC OSCILLATION ALONG WITH
CROSS POLAR FLOW FAVOR A TRANSITION TO COLDER TEMPERATURES ACROSS THE CENTRAL
AND EASTERN U.S. DURING EARLY JANUARY. ALTHOUGH BELOW-NORMAL TEMPERATURES ARE
FORECAST TO OVERSPREAD THE GREAT PLAINS AND MIDWEST LATER IN WEEK-2, THE
MAGNITUDE OF THE ANOMALOUS COLD DIFFERS AMONG MODEL SOLUTIONS. THE GEFS AND
CANADIAN ENSEMBLE MEANS DEPICT DAILY TEMPERATURE ANOMALIES OF MORE THAN -10
DEGREES F BELOW NORMAL, WHILE THE ECMWF ENSEMBLE MEAN IS MORE MODEST WITH ONLY
A -5 DEGREES F DEPARTURE FROM NORMAL. FROM JANUARY 5-8, A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR THE NORTHERN GREAT PLAINS WHERE THE
GEFS DEPICTS MINIMUM TEMPERATURES HAVING A 20 PERCENT CHANCE OF FALLING BELOW
THE 15TH PERCENTILE AND -10 DEGREES F.
ENHANCED ONSHORE FLOW FAVORS ABOVE-NORMAL PRECIPITATION THROUGHOUT SOUTHERN
ALASKA. HOWEVER, PRECIPITATION AMOUNTS ARE NOT EXPECTED TO BE HAZARDOUS DURING
WEEK-2.
FORECASTER: BRAD PUGH
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