573
FXUS21 KWNC 302049
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 30 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS EXPECTED TO SHIFT FROM THE WESTERN
CONTIGUOUS U.S. (CONUS) TO THE CENTRAL CONUS DURING WEEK-2, WHICH FAVORS A
BROAD AREA OF HIGH WINDS AND AREAS OF HIGH ELEVATION HEAVY SNOWFALL FOR THE
WEST. A SURFACE LOW PRESSURE SYSTEM IS FAVORED TO DEVELOP OVER THE
NORTHWESTERN GULF OF MEXICO BY THE MIDDLE OF WEEK-2, BRINGING INCREASED CHANCES
OF HEAVY PRECIPITATION TO SOUTHERN PORTIONS OF THE EAST-CENTRAL CONUS. STRONG
MID-LEVEL LOW PRESSURE 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 SNOW FOR THE HIGHER ELEVATIONS OF THE CASCADES, AND PARTS
OF THE SIERRA NEVADAS, FRI, DEC 8.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST
AND ROCKIES, FRI-MON, DEC 8-11.
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, FRI-TUE, DEC 8-12.
SLIGHT RISK OF HIGH WINDS FOR SOUTHEAST ALASKA, FRI-SUN, DEC 8-10.
DETAILED SUMMARY
FOR SUNDAY DECEMBER 03 - THURSDAY DECEMBER 07:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY DECEMBER 08 - THURSDAY DECEMBER 14: BY THE BEGINNING OF WEEK-2, THE
PRECIPITATION ASSOCIATED WITH ONSHORE FLOW FROM WASHINGTON SOUTHWARD THROUGH
NORTHERN CALIFORNIA IS EXPECTED TO DIMINISH. A SLIGHT RISK OF HEAVY SNOW IS
INDICATED FOR THE OREGON CASCADES, AND PORTIONS OF THE SISKIYOUS AND SIERRAS IN
CALIFORNIA AT THE START OF THE PERIOD, DEC 8. ENERGY ASSOCIATED WITH A
MID-LEVEL TROUGH IS FORECAST TO TRAVERSE THE ROCKIES, ELEVATING THE CHANCES FOR
HEAVY SNOWFALL ACROSS PORTIONS OF THE EASTERN INTERMOUNTAIN REGION AND ROCKIES,
DEC 8-11. THOUGH BOTH THE GFS AND ECMWF ENSEMBLES DEPICT SEVERAL PULSES OF
MOISTURE AFFECTING THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA DURING THE
MIDDLE AND LATTER PORTIONS OF WEEK-2, THE PRECIPITATION AMOUNTS ARE EXPECTED TO
REMAIN BELOW HAZARDOUS THRESHOLDS. THE INTEGRATED VAPOR TRANSPORT (IVT) TOOL
CONFIRMS THIS IDEA, DEPICTING A SIGNIFICANTLY REDUCED CHANCE FOR ATMOSPHERIC
RIVER (AR) ACTIVITY DURING THIS PERIOD. STRONG SURFACE HIGH PRESSURE IS
PREDICTED TO MOVE SOUTHEASTWARD OUT OF WESTERN CANADA, FAVORING A SLIGHT RISK
OF HIGH WINDS (AT LEAST 20-25 MPH) ACROSS MUCH OF THE WESTERN THIRD OF THE
CONUS DURING WEEK-2.
AS THE AFOREMENTIONED SURFACE HIGH MOVES SOUTHEASTWARD ACROSS THE ROCKIES AND
HIGH PLAINS, EASTERLY UPSLOPE FLOW MAY BRING ACCUMULATING SNOWFALL TO THE
CENTRAL AND SOUTHERN HIGH PLAINS AND ROCKIES. AT THIS TIME HOWEVER, SNOWFALL
AMOUNTS ARE EXPECTED TO REMAIN BELOW HAZARDOUS THRESHOLDS. THE ECMWF AND GFS
ENSEMBLES PREDICT A DEEPENING MID-LEVEL TROUGH ACROSS THE SOUTHWEST AND
SOUTHERN ROCKIES DURING THE EARLY PORTION OF WEEK-2. BY THE MIDDLE OF THE
PERIOD, THIS MID-LEVEL ENERGY 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 SLIGHT RISK OF HEAVY PRECIPITATION IS
DEPICTED FOR A SIGNIFICANT FRACTION OF THE SOUTHEASTERN QUARTER OF THE CONUS
FROM DEC 10-12. PRECIPITATION AMOUNTS OF ABOUT AN INCH ARE EXPECTED, SUPPORTED
BY THE GEFS AND ECMWF ENSEMBLE PROBABILISTIC EXTREMES TOOL (PET) FOR
PRECIPITATION. PRECIPITATION ASSOCIATED WITH THE NORTHERN PORTION OF THIS STORM
SYSTEM IS PREDICTED TO MOVE ACROSS THE OHIO VALLEY, MID-ATLANTIC REGION, AND
NORTHEAST, THOUGH AMOUNTS ARE EXPECTED TO REMAIN SUB-HAZARDOUS. GIVEN CURRENT
UNCERTAINTIES IN THE STORM’S TRACK AND INTENSITY, IT IS DIFFICULT AT BEST TO
DELINEATE AREAS OF SNOW FROM RAIN, THOUGH INTERIOR PORTIONS OF NEW ENGLAND AND
THE NORTHEAST HAVE A BETTER CHANCE AT RECEIVING ACCUMULATING SNOW WITH THIS
SYSTEM.
PERSISTENT SURFACE LOW PRESSURE OVER THE NORTHERN GULF OF ALASKA SUPPORTS
ONSHORE FLOW ACROSS SOUTHEAST ALASKA, WITH PERHAPS SEVERAL INCHES OF
PRECIPITATION. AT THIS TIME, NO PRECIPITATION HAZARD IS POSTED FOR THE AREA.
HOWEVER, THERE IS A CONTINUING SLIGHT RISK OF HIGH WINDS (AT LEAST 40 MPH) FOR
SOUTHEAST ALASKA FROM DEC 8-10, IN ADVANCE OF THE MEAN SURFACE LOW AS IT SLOWLY
TRACKS EASTWARD.
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 SOUTHWESTERN PORTIONS 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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