893
FXUS21 KWNC 012041
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 01 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE INITIALLY OVER THE WEST-CENTRAL CONTIGUOUS
U.S. (CONUS) IS EXPECTED TO PROGRESS INTO THE EASTERN CONUS DURING THE WEEK-2
PERIOD. THIS FAVORS A BROAD AREA OF INCREASED POTENTIAL FOR HIGH WINDS ACROSS
MUCH OF THE WESTERN HALF OF THE LOWER 48 STATES, AND HIGH ELEVATION HEAVY
SNOWFALL FOR MUCH OF THE ROCKIES AND ADJACENT HIGH PLAINS. A LARGE, BUT
RELATIVELY DISORGANIZED, LOW PRESSURE SYSTEM IS FORECAST TO BRING WIDESPREAD
PRECIPITATION TO MUCH OF THE EASTERN HALF OF THE CONUS, WITH THE GREATEST
CHANCES FOR AMOUNTS REACHING HAZARDOUS THRESHOLDS OVER SOUTHERN PORTIONS OF THE
EAST-CENTRAL CONUS. FARTHER NORTH, MID-LEVEL LOW PRESSURE OVER ALASKA AND THE
GULF OF ALASKA IS LIKELY TO MAINTAIN STORMY CONDITIONS OVER SOUTHEAST ALASKA
DURING THE FORECAST PERIOD.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE VICINITY OF THE LOWER MISSISSIPPI
AND TENNESSEE VALLEYS, SOUTHERN OHIO VALLEY, AND THE EAST-CENTRAL GULF COAST
REGION, SUN-TUE, DEC 10-12.
SLIGHT RISK OF HEAVY PRECIPITATION FOR SOUTHEAST ALASKA, SAT-WED, DEC 9-13.
SLIGHT RISK OF HEAVY SNOW FOR MUCH OF THE ROCKIES AND ADJACENT HIGH PLAINS,
SAT-MON, DEC 9-11.
SLIGHT RISK OF HIGH WINDS FROM THE HIGH PLAINS WESTWARD TO THE PACIFIC COAST,
EXCLUDING THE PACIFIC NORTHWEST, NORTHERN INTERMOUNTAIN REGION, AND PARTS OF
THE NORTHERN ROCKIES, SAT-WED, DEC 9-13.
DETAILED SUMMARY
FOR MONDAY DECEMBER 04 - FRIDAY DECEMBER 08:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY DECEMBER 09 - FRIDAY DECEMBER 15: BY THE BEGINNING OF WEEK-2, THE
PRECIPITATION ASSOCIATED WITH ONSHORE FLOW FROM WASHINGTON SOUTHWARD THROUGH
NORTHERN CALIFORNIA IS EXPECTED TO DIMINISH. ENERGY ASSOCIATED WITH A MID-LEVEL
TROUGH IS FORECAST TO TRAVERSE THE ROCKIES AND GREAT PLAINS, ELEVATING THE
CHANCES FOR HEAVY SNOWFALL ACROSS MUCH OF THE ROCKIES AND ADJACENT HIGH PLAINS,
DEC 9-11. BY THE MIDDLE AND LATTER PORTIONS OF THE PERIOD, THE GEFS IS BULLISH
ON BRINGING ADDITIONAL PACIFIC MOISTURE TO THE WEST COAST REGION, THOUGH THE
ECMWF ENSEMBLE BACKS OFF SIGNIFICANTLY ON THIS SCENARIO. THE INTEGRATED VAPOR
TRANSPORT (IVT) TOOL CONFIRMS THIS IDEA, DEPICTING SIGNIFICANT DISCREPANCIES
BETWEEN THE GEFS AND ECMWF ENSEMBLE PRECIPITATION FORECASTS FOR THE WEST COAST.
GIVEN THIS UNCERTAINTY, NO HAZARDOUS PRECIPITATION AREA IS DESIGNATED FOR THIS
REGION IN TODAY’S HAZARDS OUTLOOK. STRONG SURFACE HIGH PRESSURE IS PREDICTED TO
MOVE SOUTHEASTWARD OUT OF ALBERTA, FAVORING A SLIGHT RISK OF HIGH WINDS (AT
LEAST 20-25 MPH) ACROSS MUCH OF THE WESTERN HALF OF THE CONUS DURING WEEK-2.
MID-LEVEL ENERGY ASSOCIATED WITH THE 500-HPA TROUGH FORECAST TO MOVE EASTWARD
FROM THE WEST-CENTRAL CONUS IS EXPECTED TO INTERACT WITH INCREASING SOUTHERLY
LOW-LEVEL RETURN FLOW FROM THE WESTERN GULF OF MEXICO, ASSOCIATED WITH SURFACE
HIGH PRESSURE OVER THE SOUTHEAST. A BROAD SWATH OF PRECIPITATION IS FAVORED TO
DEVELOP OVER THE VICINITY OF THE LOWER MISSISSIPPI VALLEY EARLY IN WEEK-2, AND
SPREAD NORTHEASTWARD AND EASTWARD WITH TIME. THOUGH THE EXPECTED SPATIAL
COVERAGE OF PRECIPITATION IS WIDESPREAD WITH THIS SYSTEM, THE AREA OF
ANTICIPATED HEAVY PRECIPITATION (AN INCH OR MORE WITHIN A 3-DAY PERIOD) IS
SUBSTANTIALLY SMALLER, BEING CONFINED TO SOUTHERN SECTIONS OF THE EAST-CENTRAL
CONUS, DEC 10-12. THIS IS CONSISTENT WITH THE GEFS, ECMWF, AND CANADIAN
ENSEMBLE MEANS DEPICTED IN THE PROBABILISTIC EXTREMES TOOL (PET) FOR
PRECIPITATION. THE 0Z ECMWF ENSEMBLE MEAN PREDICTS A CONSOLIDATION OF SURFACE
LOW PRESSURE TO THE LEE OF THE COLORADO ROCKIES EARLY IN WEEK-2, WHICH THEN
TRACKS NORTHEASTWARD TOWARDS THE GREAT LAKES REGION. THE 12Z GEFS PREDICTS A
SIMILAR EVOLUTION. DURING THE LAST SEVERAL DAYS, THE VARIOUS DETERMINISTIC
MODELS AND ENSEMBLES HAVE FLUCTUATED BETWEEN TWO POSSIBLE AREAS FOR STORM
DEVELOPMENT; THE CENTRAL HIGH PLAINS AND THE WESTERN GULF OF MEXICO. THIS,
ALONG WITH LIMITED MOISTURE INFLOW FROM THE GULF OF MEXICO, MAY EXPLAIN WHY THE
MODELS STILL DO NOT PREDICT A SINGLE, STRONG LOW PRESSURE SYSTEM WITH THIS
EVENT.
PERSISTENT SURFACE LOW PRESSURE OVER THE NORTHERN GULF OF ALASKA SUPPORTS
ONSHORE FLOW ACROSS SOUTHEAST ALASKA, WITH 2-4 INCHES OF PRECIPITATION
ANTICIPATED, THOUGH LOCAL AMOUNTS COULD BE SIGNIFICANTLY GREATER. THIS IS
CONSISTENT WITH BOTH UNCALIBRATED AND CALIBRATED PRECIPITATION TOOLS.
THEREFORE, A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR THE AREA, DEC
9-13. INDIVIDUAL STORM SYSTEMS THAT AFFECT SOUTHEAST ALASKA WILL LIKELY BRING
FAIRLY HIGH WINDS TO THE AREA, THOUGH THERE IS TOO MUCH UNCERTAINTY AMONG THE
MODELS AT THIS TIME TO DESIGNATE A WIND HAZARD.
FOR TEMPERATURES, THERE IS BETTER MODEL AGREEMENT IN REGARDS TO STRONGER
RIDGING OVER THE BERING SEA WHERE INCREASED NORTHERLY FLOW APPEARS MORE LIKELY
TO BRING BELOW NORMAL TEMPERATURES TO MUCH OF THE STATE DURING WEEK-2. MINIMUM
TEMPERATURES ARE NOT EXPECTED TO REACH HAZARD CRITERIA, HOWEVER THE ARRIVAL OF
COLDER TEMPERATURES FOLLOWING A VERY WARM NOVEMBER IS LIKELY TO AID IN RIVER
FREEZES. A RECENT AERIAL FREEZE-UP SURVEY FOUND OPEN WATER AND THIN ICE ALONG
THE KUSKOKWIM RIVER WHICH MAKES RIVER TRAVEL HAZARDOUS.
FORECASTER: ANTHONY ARTUSA
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