330
FXUS21 KWNC 271944
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 27 2024
SYNOPSIS: COLD HIGH PRESSURE SHOULD BE EXITING THE EASTERN CONUS AS WEEK-2
STARTS, BUT MUCH BELOW NORMAL TEMPERATURES MAY BE OBSERVED IN PART OF THE SOUTH
ATLANTIC REGION THE FIRST MORNING OF THE PERIOD. AFTER THAT, ONE OR MORE
SURFACE HIGH PRESSURE SYSTEMS ARE EXPECTED TO ADVANCE SOUTHEASTWARD INTO THE
CENTRAL AND EASTERN CONTIGUOUS U.S. (CONUS), INCREASING THE ODDS FOR MUCH BELOW
NORMAL TEMPERATURES IN PART OF UPPER NEW ENGLAND LATER IN THE PERIOD, ALTHOUGH
A DETAILED EVOLUTION OF THE PATTERN CAN’T BE DETERMINED AT THIS TIME. THE
SURFACE PRESSURE GRADIENT BETWEEN THESE HIGH PRESSURE SYSTEMS AND LOWER
PRESSURES IN SOUTHEASTERN CANADA RAISES A RISK OF PERIODIC HIGH WINDS USHERING
THE COLDER AIR INTO THE CENTRAL AND EASTERN CONUS. THIS COLD AIR WILL BE
OVERRUNNING THE UNUSUALLY WARM GREAT LAKES, SETTING THE STAGE FOR LAKE-ENHANCED
SNOW SHOWERS AND SQUALLS OVER CLIMATOLOGICALLY-FAVORED AREAS DOWNWIND OF THE
LAKES EARLY WEEK-2 BEFORE THE WIND TRAJECTORY MAY BECOME LESS FAVORABLE.
MEANWHILE, ONE OR MORE STORM SYSTEMS COULD AFFECT SOUTHERN ALASKA, BRINGING THE
POTENTIAL FOR PERIODIC HEAVY PRECIPITATION AND HIGH WINDS TO SOUTH-CENTRAL AND
SOUTHEASTERN ALASKA.
HAZARDS
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IN PORTIONS OF THE SOUTH ATLANTIC
REGION, THU, DEC 5.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IN THE UPPER NORTHEAST, SAT-WED,
DEC 7-11.
SLIGHT RISK OF HEAVY SNOW IN THE CLIMATOLOGICALLY-FAVORED REGIONS FOR
LAKE-ENHANCED SNOWFALL IN THE CENTRAL AND WESTERN GREAT LAKES, THU-SAT, DEC 5-7.
SLIGHT RISK OF HEAVY SNOW IN CLIMATOLOGICALLY-FAVORED REGIONS FOR LAKE-ENHANCED
SNOWFALL IN THE EASTERN GREAT LAKES AND THE CENTRAL AND NORTHERN APPALACHIANS,
AND ALONG WESTERN PARTS OF THE PIEDMONT IN THE MID-ATLANTIC AND NORTHEAST,
THU-SAT, DEC 5-7.
SLIGHT RISK FOR PERIODIC HIGH WINDS OVER CENTRAL AND NORTHERN PORTIONS OF THE
CONUS FROM THE GREAT PLAINS TO THE EAST COAST, THU-WED, DEC 5-11.
SLIGHT RISK OF HEAVY PRECIPITATION IN SOUTH-CENTRAL AND SOUTHEASTERN ALASKA,
THU-WED, DEC 5-11.
DETAILED SUMMARY
FOR SATURDAY NOVEMBER 30 - WEDNESDAY DECEMBER 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY DECEMBER 05 - WEDNESDAY DECEMBER 11: THE ENSEMBLE MEANS ALL
GENERALLY AGREE THAT A BROAD MID-LEVEL SHOULD EXTEND ACROSS THE EASTERN
ONE-THIRD TO ONE-HALF OF NORTH AMERICA WHILE MID-LEVEL RIDGING OCCURS FARTHER
WEST. THIS PATTERN FAVORS A SERIES OF COLD HIGH PRESSURE SYSTEMS DROPPING INTO
THE CENTRAL AND/OR EASTERN CONUS DURING THE PERIOD, BUT THERE CONTINUES TO BE
SIGNIFICANT UNCERTAINTY AMONG THE VARIOUS TOOLS REGARDING THE SPECIFICS OF
EVOLUTION (STRENGTH, TIMING, AND LOCATION OF INDIVIDUAL FEATURES). THERE IS
EVEN A LITTLE MORE UNCERTAINTY TODAY IN THE HEAVY SNOW AND COLD WEATHER HAZARDS
RISKS, AS SOME TOOLS TRACK HIGH AND LOW PRESSURE SYSTEMS IN EASTERN NORTH
AMERICA IN A WAY THAT IS LESS CONDUCIVE TO LAKE-ENHANCED SNOWFALL AND STRONG
WINDS.
THERE IS A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IN PART OF THE SOUTH
ATLANTIC REGION ON THE FIRST MORNING OF WEEK-2 AS A COLD HIGH PRESSURE SYSTEM
PUSHES OFF THE EAST COAST, ALLOWING TEMPERATURES TO MODERATE QUICKLY. LATER IN
THE WEEK, MORE COLD HIGH PRESSURE IS EXPECTED TO AFFECT THE CENTRAL AND/OR
EASTERN CONUS, BUT THERE IS A LARGE ARRAY OF POSSIBILITIES AMONG THE TOOLS
REGARDING THE DAY-TO-DAY EVOLUTION AND STRENGTH OF THE COLD AIR PUSHING INTO
THE COUNTRY. GENERALLY, THE GEFS MEAN AND CANADIAN ENSEMBLE MEAN ARE WEAKER
THAN THE EUROPEAN ENSEMBLE MEAN WITH THE COLD AIR LATER WEEK-2, AND THE
EUROPEAN ENSEMBLE MEAN PUSHES THE MOST ANOMALOUSLY COLD AIR INTO THE NORTHEAST
WHILE THE OTHER TWO FAVOR TEMPERATURES SOMEWHAT CLOSER TO NORMAL WITH THE CORE
OF THE COLDER AIR TRACKING FARTHER TO THE SOUTHWEST, INTO THE GREAT LAKES
REGION AND PARTS OF THE LOWER OHIO AND MISSISSIPPI VALLEYS. IT IS DIFFICULT TO
DETERMINE WHICH SCENARIO IS MORE LIKELY, BUT ACCORDING TO THE EUROPEAN
ENSEMBLES, THERE IS A 20 TO 40 PERCENT CHANCE THAT TEMPERATURES COULD EXCEED 20
DEG. F BELOW NORMAL DURING THE MIDDLE AND LATER PART OF THE PERIOD. WHILE THE
OTHER ENSEMBLES ARE CONSIDERABLY MILDER AND KEEP THE CORE OF THE NEGATIVE
TEMPERATURE ANOMALIES FARTHER SOUTHWEST, THE PERSISTENCE AND POTENTIAL
MAGNITUDE OF THE COLD WEATHER IN THE EUROPEAN ENSEMBLES JUSTIFIES INTRODUCING A
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IN PARTS OF THE UPPER NORTHEAST
DURING THE MIDDLE AND LATTER PARTS OF WEEK-2. THE REGION IS RESTRICTED TO AREAS
WITH SIGNIFICANT CHANCES FOR TEMPERATURES TO DROP BELOW 0 DEG. F ON MULTIPLE
NIGHTS, AND WHERE THE PROBABILISTIC EXTREMES TOOL (PET) BASED ON THE EUROPEAN
ENSEMBLES SHOWS ODDS EXCEEDING 30 PERCENT FOR TEMPERATURES TO DROP INTO THE
COLDEST 15 PERCENT OF THE CLIMATOLOGICAL DISTRIBUTION ON MULTIPLE NIGHTS. IF
THE SITUATION EVOLVES MORE LIKE THE GEFS AND CANADIAN ENSEMBLES DEPICT,
SUBNORMAL TEMPERATURES WOULD STILL COVER MOST OF THE EASTERN HALF OF THE CONUS,
BUT TEMPERATURES WOULD LIKELY REMAIN ABOVE HAZARDS THRESHOLDS.
COLD CANADIAN AIR STREAMING ACROSS THE UNUSUALLY WARM WATERS OF THE GREAT LAKES
WOULD PROMOTE LOCALLY HEAVY LAKE-ENHANCED SNOWFALL CLIMATOLOGICALLY-FAVORED
SNOWBELT AREAS DOWNWIND OF THE LAKES. FOR NOW, THE SLIGHT CHANCE FOR HEAVY SNOW
DOWNWIND OF THE GREAT LAKES AND INTO THE CENTRAL APPALACHIANS REMAINS IN PLACE
FOR THE FIRST FEW DAYS OF THE PERIOD, BUT CONFIDENCE IS A LITTLE LOWER THAN
YESTERDAY BECAUSE OF THE INCREASED UNCERTAINTY IN THE EVOLUTION OF COLD
CANADIAN HIGH PRESSURE SINKING INTO THE CONUS, WITH SOME TOOLS SHOWING A LESS
FAVORABLE SET-UP FOR LAKE-ENHANCED SNOWFALL. MODELS CONTINUE TO DIVERGE AS
WEEK-2 PROGRESSES, REDUCING THE ODDS FOR HEAVY SNOW AND ENDING THE SLIGHT RISK
AREAS. SOME MODELS FORECAST ONE OR MORE WEAK MID-LATITUDE LOW PRESSURE SYSTEMS
TRACKING THROUGH THE NORTHEASTERN QUARTER OF THE CONUS, BUT THEY SHOULD BE
RELATIVELY MOISTURE-STARVED AND ARE THUS UNLIKELY TO TRIGGER HAZARDOUS AMOUNTS
OF HEAVY SNOW.
TO THE SOUTH OF THIS SERIES OF COLD HIGH PRESSURE SYSTEMS, SOME TOOLS SHOW
ENHANCED CHANCES FOR HEAVY PRECIPITATION EARLY WEEK-2 IN PART OF THE SOUTHERN
CONUS. THE BEST MODEL AGREEMENT FOR ENHANCED PRECIPITATION IS ACROSS EASTERN
TEXAS, WITH AT LEAST SOME GUIDANCE POINTING TOWARD HEAVY PRECIPITATION ANYWHERE
FROM DEEP SOUTH TEXAS INTO THE LOWER MISSISSIPPI VALLEY. THERE IS CONSIDERABLE
UNCERTAINTY ABOUT THIS POTENTIAL, AND EVEN THE MOST AGGRESSIVE TOOLS ARE NOT
REMARKABLY WETTER THAN HAZARDS THRESHOLDS, SO FOR NOW, NO HAZARD IS POSTED.
WHILE ONE OR MORE COLD HIGH PRESSURE SYSTEMS SINK FROM CANADA INTO THE CENTRAL
AND EASTERN CONUS, THERE MAY BE A SHARP ENOUGH PRESSURE GRADIENT TO PROMOTE
HIGH WINDS AT TIMES OVER PARTS OF THE CENTRAL AND EASTERN CONUS, BUT AS IS THE
CASE WITH THE OTHER HAZARDS, THE INCREASED UNCERTAINTY IN THE DAY-TO-DAY
FORECASTS REDUCES THE CONFIDENCE IN THIS DEVELOPMENT, BUT ANYTIME COLD CANADIAN
HIGH PRESSURE IS TRACKING INTO THE CENTRAL AND EASTERN CONUS, THERE IS THE
POTENTIAL FOR ONE OR MORE PERIODS OF HAZARDOUSLY STRONG WINDS TO DEVELOP.
GUIDANCE REMAINS FAIRLY ROBUST WITH THE POTENTIAL FOR A SERIES OF STRONG LOW
PRESSURE SYSTEMS TO TRACK ACROSS OR NEAR THE GULF OF ALASKA. THE TIMING,
STRENGTH, AND TRACK OF INDIVIDUAL STORM SYSTEMS IS HIGHLY UNCERTAIN, BUT A
LARGE-SCALE PATTERN FAVORABLE FOR PERIODS OF STORMY WEATHER IS EXPECTED ALONG
PARTS OF THE SOUTHERN TIER OF ALASKA THROUGHOUT WEEK-2. FOR THIS REASON, A
SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR SOUTH-CENTRAL AND SOUTHEASTERN
ALASKA FOR THE ENTIRETY OF THE PERIOD. IN ADDITION, STRONG WINDS WILL BE
POSSIBLE AT TIMES ACROSS THE ENTIRE SOUTHERN TIER OF THE STATE, INCLUDING PARTS
OF THE ALEUTIANS. RIGHT NOW, HOWEVER, IT APPEARS THAT DANGEROUSLY HIGH WINDS
WILL PRIMARILY AFFECT OFFSHORE AREAS, SO NO HIGH WIND HAZARD IS POSTED, BUT
THIS SITUATION WILL NEED TO BE CLOSELY MONITORED FOR SIGNS THAT STRONGER WINDS
MAY OCCUR INLAND.
FORECASTER: RICH TINKER
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