877
FXUS21 KWNC 281906
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 28 2023
SYNOPSIS: A DEPARTING SURFACE LOW FAVORED OVER THE NORTHEASTERN CONTIGUOUS U.S.
(CONUS) MAY BRING LOCALLY HEAVY SNOWFALL, ALONG WITH EPISODES OF HIGH WINDS TO
MANY PARTS OF THE EASTERN U.S. EARLY IN THE PERIOD. ACROSS THE WEST, ENHANCED
ONSHORE FLOW IS FAVORED TO PERSIST FROM LATE WEEK-1 INTO EARLY WEEK-2,
SUSTAINING THE RISKS OF HEAVY PRECIPITATION, HIGH ELEVATION SNOWFALL AND HIGH
WINDS FOR MUCH OF THE WESTERN CONUS. OVER ALASKA, STRONG MID-LEVEL LOW
PRESSURE IS LIKELY TO MAINTAIN STORMY CONDITIONS OVER THE SOUTH-CENTRAL
MAINLAND AND THE SOUTHEAST INTO EARLY NEXT WEEK.
HAZARDS
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE GREAT LAKES, APPALACHIANS, AND THE
NORTHEAST, WED, DEC 6.
SLIGHT RISK OF HIGH WINDS FOR THE NORTHEASTERN CONUS, WED, DEC 6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, WED-THU, DEC 6-7.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE CASCADES, AND PARTS
OF THE SIERRA NEVADAS, WED-THU, DEC 6-7.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST
AND ROCKIES, WED-SUN, DEC 6-10.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF SOUTHERN CALIFORNIA, DEC 6-7.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST INCLUDING THE NORTHERN HIGH
PLAINS, WED-SUN, DEC 6-10.
SLIGHT RISK OF HIGH WINDS FOR THE KENAI PENINSULA OF ALASKA, COASTAL SOUTHERN
ALASKA, AND THE SOUTHEAST, WED-FRI, DEC 6-8.
DETAILED SUMMARY
FOR FRIDAY DECEMBER 01 - TUESDAY DECEMBER 05:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY DECEMBER 06 - TUESDAY DECEMBER 12: THE WEEK-2 HAZARDS PERSPECTIVE
LARGELY REMAINS ON TRACK BASED ON THE LATEST GUIDANCE. BOTH THE ECMWF AND GEFS
ENSEMBLE MEAN 500-HPA HEIGHT FORECASTS CONTINUE TO FEATURE ANOMALOUS 500-HPA
RIDGING CENTERED OVER THE ROCKIES EARLY NEXT WEEK, AND A DOWNSTREAM TROUGH THAT
INITIALLY AMPLIFIES OVER THE EASTERN CONUS EARLY IN THE PERIOD, AND GRADUALLY
LIFTS OUT OVER THE CANADIAN MARITIMES TOWARDS THE MIDDLE OF THE NEXT WEEK. THIS
PATTERN IS EXPECTED TO PRODUCE A POTENTIALLY STRONG LOW PRESSURE SYSTEM THAT
TRACKS ACROSS THE EASTERN U.S LATE IN WEEK-1. THERE IS STILL A FAIR AMOUNT OF
UNCERTAINTY REGARDING THE TIMING AND DETAILS OF STORM TRACK DUE TO DIFFERENCES
IN THE ENSEMBLES, THOUGH MUCH OF THE WEATHER RELATED HAZARDS LOOK TO TIME OFF
BY THE START OF WEEK-2, WITH SOME HAZARD POTENTIAL POTENTIALLY LINGERING INTO
THE START OF WEEK-2.
BASED ON UNCALIBRATED PRECIPITATION GUIDANCE, THE HIGHEST PRECIPITATION AMOUNTS
TIED TO THE MEAN LOW ARE FAVORED TO WELL OFFSHORE BY DAY 8 (DEC 6), PROMPTING
THE REMOVAL OF A SLIGHT RISK OF HEAVY PRECIPITATION OVER THE NORTHEASTERN CONUS
IS TODAY'S HAZARD OUTLOOK. HOWEVER, A SLIGHT RISK OF HEAVY SNOW REMAINS ISSUED
FOR DAY 8 OVER THE GREAT LAKES AND THE NORTHEAST GIVEN RESIDUAL MOISTURE
FAVORED ON THE BACKSIDE OF THE MEAN LOW, WHICH IS SUPPORTED BY SIGNALS IN THE
GEFS SNOW WATER EQUIVALENT (SWE) PROBABILISTIC EXTREMES TOOL (PET) AS WELL AS
DETERMINISTIC SOLUTIONS. WITH THE MEAN LOW FAVORED TO DEEPEN UNDER THE
AMPLIFYING TROUGHING ALOFT, A SLIGHT RISK OF HIGH WINDS ALSO REMAINS ISSUED FOR
DAY 8 BEFORE CALMER CONDITIONS BEGIN TO SETTLE IN OVER THE EASTERN CONUS LATER
IN PERIOD. COOLER TEMPERATURES ARE LIKELY IN THE WAKE OF THE PREDICTED FRONTAL
SYSTEM WITH THE HIGHEST CHANCES FOR BELOW-NORMAL TEMPERATURES OVER PARTS OF THE
SOUTHEAST EARLY IN THE PERIOD. WHILE MINIMUM TEMPERATURES ARE NOT EXPECTED TO
FALL BELOW HAZARDS THRESHOLDS ACROSS MUCH OF THE EASTERN U.S, NEAR FREEZING
TEMPERATURES ARE POSSIBLE ACROSS PARTS OF THE COASTAL CAROLINAS, GEORGIA, AND
NORTHERN FLORIDA WHERE FIRST FREEZES HAVE NOT BEEN REGISTERED FOR THE FALL.
UPSTREAM, A DEEP 500-HPA TROUGHING REMAINS FAVORED OVER THE NORTHEASTERN
PACIFIC, WHERE ENHANCED ONSHORE FLOW AND ABOVE-NORMAL PRECIPITATION IS FAVORED
OVER MUCH OF THE NORTHWESTERN CONUS. THE ECMWF HAS BECOME MORE AMPLIFIED WITH
THIS MID-LEVEL FEATURE THAN THE GEFS EARLY IN THE PERIOD, RESULTING IN LARGER
DISCREPANCIES IN BOTH PRECIPITATION TOOLS RELATIVE TO YESTERDAY. ADDING TO
MORE UNCERTAINTY IS THE CANADIAN ENSEMBLE, WHICH FEATURES RISING MID-LEVEL
HEIGHTS TO PROMOTE DRIER CONDITIONS OVER THE WEST COAST THROUGH THE MIDDLE OF
WEEK-2. WHILE THE BULK OF THE HEAVY PRECIPITATION POTENTIAL APPEARS TO BE
TIMING OUT, A SLIGHT RISK OF HEAVY PRECIPITATION REMAINS ISSUED FOR DEC 6-7
BASED ON UNCALIBRATED PRECIPITATION GUIDANCE AND LINGERING SIGNALS IN THE
INTEGRATED VAPOR TRANSPORT (IVT) TOOLS. WHILE THE ENHANCEMENT OF PRECIPITATION
IS EXPECTED TO BE BENEFICIAL FOR AREAS EXPERIENCING DROUGHT, ANY LOCALLY HEAVY
PRECIPITATION OVER BURN SCARRED AREAS WITHIN THE HIGHLIGHTED AREA MAY LEAD TO
LOCALIZED FLOODING AND/OR DEBRIS FLOWS.
GIVEN THE POTENTIAL FOR ONSHORE FLOW OVER THE WEST COAST, AS WELL AS
INDICATIONS OF MID-LEVEL TROUGHING AND INCREASED MOISTURE SHIFTING EASTWARD
WITH TIME IN THE GEFS AND ECMWF, A SLIGHT RISK OF HEAVY SNOW IS POSTED OVER THE
HIGHER ELEVATIONS OF THE CASCADES AND PARTS OF THE SIERRA NEVADAS FOR DEC 6-7,
AND OVER THE PARTS OF INTERMOUNTAIN WEST AND NORTHERN ROCKIES FOR DEC 6-10.
ACCOMPANYING THE EXTENDED SNOW RISK, A SLIGHT RISK OF HIGH WINDS IS ALSO ISSUED
FOR MUCH OF THE WESTERN CONUS AND INCLUDING THE NORTHERN PLAINS FOR DEC 6-10
BASED ON THE EVOLUTION OF THE PATTERN ALOFT AND PET TOOLS. A SLIGHT RISK OF
HIGH WINDS REMAINS POSTED FOR PARTS OF SOUTHERN CALIFORNIA, BUT IS NOW VALID
THROUGH DEC 7 BEFORE MUCH OF SURFACE HIGH PRESSURE BEGINS TO BREAK DOWN OVER
THE GREAT BASIN AND REDUCE THE POTENTIAL FOR EPISODES OF SANTA ANA WINDS.
TIED TO THE AFOREMENTIONED MID-LEVEL TROUGHING OVER THE NORTHEASTERN PACIFIC,
STRONG SURFACE LOW PRESSURE REMAINS FAVORED OVER THE GULF OF ALASKA WHICH IS
EXPECTED TO PROLONG STORMY CONDITIONS OVER SOUTHEASTERN ALASKA INTO WEEK-2. THE
STRONG MEAN PRESSURE GRADIENTS EVIDENT IN BOTH THE GEFS AND ECMWF, AS WELL AS
PETS SUPPORT A SLIGHT RISK OF HIGH WINDS EXTENDING FROM THE KENAI PENINSULA TO
THE SOUTHEAST FOR DEC 6-8. ALTHOUGH PRECIPITATION AMOUNTS ARE NOT LIKELY TO
EXCEED HAZARD THRESHOLDS BASED ON PET GUIDANCE, THE CONTINUATION OF
ABOVE-NORMAL PRECIPITATION AND HIGH WINDS ARE LIKELY TO WORSEN ALREADY
SATURATED SOILS, AND MAY LEAD TO ADDITIONAL LANDSLIDES OVER PARTS OF THE STATE.
FOR TEMPERATURES, THERE IS BETTER MODEL AGREEMENT IN REGARDS TO STRONGER
RIDGING OVER THE BERING STRAIT WHERE INCREASED NORTHERLY FLOW APPEARS MORE
LIKELY TO BRING NEAR TO BELOW NORMAL TEMPERATURES OVER THE 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: NICK NOVELLA
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