842
FXUS21 KWNC 271918
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 27 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS FORECAST TO BUILD ALONG THE WEST COAST,
WHILE MID-LEVEL LOW PRESSURE STRENGTHENS OVER THE EAST. THIS PATTERN FAVORS
ARCTIC HIGH PRESSURE SHIFTING SOUTH FROM CANADA DURING EARLY JANUARY AND THE
COLDEST TEMPERATURES SO FAR THIS WINTER ARE EXPECTED TO OVERSPREAD THE NORTHERN
GREAT PLAINS AND MIDWEST. AN INCREASED RISK OF A WINTER STORM IS FORECAST TO
SHIFT FROM THE MIDWEST TO THE NORTHEAST FROM JANUARY 4 TO 10.
HAZARDS
SLIGHT RISK OF HEAVY SNOW SHIFTING EAST FROM THE NORTHERN AND CENTRAL ROCKIES
TO THE MIDWEST, SAT-TUE, JAN 4-7.
SLIGHT RISK OF HEAVY SNOW FOR THE PORTIONS OF THE NORTHEAST AND CENTRAL
APPALACHIANS, TUE-FRI, JAN 7-10.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE FLORIDA
PANHANDLE AND NORTH-CENTRAL FLORIDA PENINSULA, SAT-SUN, JAN 4-5 AND THU-FRI,
JAN 9-10.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES SHIFTING SOUTHEASTWARD FROM THE
NORTHERN GREAT PLAINS TO THE OHIO VALLEY, SUN-FRI, JAN 5-10.
DETAILED SUMMARY
FOR MONDAY DECEMBER 30 - FRIDAY JANUARY 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY JANUARY 04 - FRIDAY JANUARY 10: ON JANUARY 4 AND 5, THE GFS AND
ECMWF ENSEMBLE MEANS DEPICT SURFACE HIGH PRESSURE BECOMING CENTERED OVER THE
SOUTHEAST WHICH COULD LEAD TO A FREEZE FOR THE FLORIDA PANHANDLE AND THE
NORTH-CENTRAL FLORIDA PENINSULA. A SLIGHT RISK OF MUCH BELOW-NORMAL
TEMPERATURES IS POSTED WHERE THE GEFS AND ECENS PROBABILISTIC EXTREMES TOOLS
(PETS) DEPICT MINIMUM TEMPERATURES HAVING MORE THAN A 20 PERCENT CHANCE OF
FALLING BELOW FREEZING. SINCE A WIDESPREAD HARD FREEZE (MINIMUM TEMPERATURES AT
OR BELOW 28 DEGREES F) IS NOT EXPECTED, A MODERATE RISK IS NOT INCLUDED.
EARLY IN WEEK-2, THE GEFS AND CMCE DEPICT A SHORTWAVE TROUGH TRACKING
SOUTHEASTWARD ACROSS THE NORTHERN TO CENTRAL ROCKIES WHICH COULD LEAD TO A
PERIOD OF HEAVY SNOW. THIS SHORTWAVE TROUGH MAY RESULT IN SURFACE LOW
DEVELOPMENT ACROSS THE CENTRAL GREAT PLAINS WITH A SUBSEQUENT TRACK EASTWARD
ACROSS THE OHIO VALLEY. BASED ON ENSEMBLE LOW TRACKS, 24-HOUR PRECIPITATION
AMOUNTS FROM THE GEFS AND ECENS, AND THE GEFS PET, THE SLIGHT RISK OF HEAVY
SNOW IS FORECAST TO SHIFT EAST FROM THE NORTHERN TO CENTRAL ROCKIES TO THE OHIO
VALLEY FROM JANUARY 4-7. PORTIONS OF THE GREAT LAKES WERE INCLUDED RELATED TO
LAKE-EFFECT SNOW. A BROAD SNOW HAZARD SHAPE IS NECESSARY DUE TO ENSEMBLE SPREAD
ON THE POTENTIAL WINTER STORM TRACK.
ALONG THE EAST COAST, THE GEFS HAS BEEN QUITE CONSISTENT WITH AN INCREASED
CHANCE OF A COASTAL LOW AND WINTER STORM ACROSS THE NORTHEAST FROM JANUARY 8-9.
SEVERAL OF THE GEFS MEMBERS DEPICT A HIGHLY IMPACTFUL WINTER STORM WITH HEAVY
SNOW FOR THE NORTHEAST, BUT A MAJORITY OF THE ECMWF ENSEMBLE MEMBERS FAVOR A
TRACK OFFSHORE OF THE EAST COAST. THE MODEL CONSENSUS AMONG THE GEFS AND ECENS
SUPPORT A SLIGHT RISK OF HEAVY SNOW (JANUARY 7-10) FROM PHILADELPHIA NORTH TO
BOSTON. THE SLIGHT RISK OF HEAVY SNOW ALSO INCLUDES AREAS DOWNWIND OF LAKES
ERIE AND ONTARIO DUE TO LAKE-EFFECT SNOW.
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. MODEL AGREEMENT BETWEEN THE GEFS AND
ECENS IS MUCH BETTER TODAY WITH THE LOCATION OF A FULL-LATITUDE RIDGE AXIS
EXTENDING NORTH FROM THE WEST COAST TO ALASKA. THE LONGWAVE PATTERN OVER NORTH
AMERICA INCREASES THE CHANCE OF AN ARCTIC AIR OUTBREAK BY MID-JANUARY BUT THERE
IS STILL UNCERTAINTY ON THE MAGNITUDE AND LOCATION OF THE ANOMALOUS COLD. THE
GEFS FAVORS A MORE EXPANSIVE AREA INCLUDING THE GREAT PLAINS, WHILE THE ECENS
FOCUSES THE ANOMALOUS COLD ACROSS THE OHIO VALLEY. BASED ON GEFS AND ECENS PETS
ALONG WITH CONSIDERATIONS OF COLD ADVISORY LEVELS, A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES IS POSTED FOR PORTIONS OF THE NORTHERN GREAT PLAINS
AND MIDWEST FROM JANUARY 5-10. THERE IS A 20 TO 40 PERCENT CHANCE OF WIND CHILL
AND/OR MINIMUM TEMPERATURES TO FALL BELOW -10 (0) DEGREES F ACROSS NORTH
DAKOTA, MINNESOTA, AND WISCONSIN (OHIO VALLEY). THIS ANOMALOUSLY COLD AIRMASS
IS FORECAST TO SHIFT SOUTH TO THE GULF COAST AND FLORIDA. A SLIGHT RISK OF MUCH
BELOW-NORMAL TEMPERATURES IS WARRANTED FOR THE FLORIDA PANHANDLE AND PORTIONS
OF THE NORTH-CENTRAL FLORIDA PENINSULA WHERE THERE IS AN ELEVATED RISK OF
FREEZING TEMPERATURES ON JANUARY 9 AND 10.
ENHANCED ONSHORE FLOW FAVORS ABOVE-NORMAL PRECIPITATION THROUGHOUT SOUTHERN
ALASKA. HOWEVER, SINCE PRECIPITATION AMOUNTS ARE NOT EXPECTED TO REACH
HAZARDOUS THRESHOLDS, NO HEAVY PRECIPITATION HAZARD IS POSTED AT THIS TIME.
FORECASTER: BRAD PUGH
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