732
FXUS21 KWNC 271937
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 27 2023
SYNOPSIS: A DEPARTING SURFACE LOW FAVORED OVER THE NORTHEASTERN CONTIGUOUS U.S.
(CONUS) MAY BRING A ROUND OF HEAVY PRECIPITATION AND 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 THE NORTHWESTERN 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 PRECIPITATION FOR PARTS OF THE MID-ATLANTIC AND THE
NORTHEAST, TUE, DEC 5.
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE GREAT LAKES, APPALACHIANS, AND THE
NORTHEAST, TUE-WED, DEC 5-6.
SLIGHT RISK OF HIGH WINDS FOR THE NORTHEASTERN CONUS, TUE-WED, DEC 5-6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, TUE-THU, DEC 5-7.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE CASCADES, NORTHERN
INTERMOUNTAIN, NORTHERN ROCKIES, TUE-THU, DEC 5-7.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST INCLUDING THE NORTHERN HIGH
PLAINS, TUE-THU, DEC 5-7.
SLIGHT RISK OF HIGH WINDS FOR THE KENAI PENINSULA OF ALASKA, COASTAL SOUTHERN
ALASKA, AND THE SOUTHEAST, TUE-THU, DEC 5-7.
DETAILED SUMMARY
FOR THURSDAY NOVEMBER 30 - MONDAY DECEMBER 04:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY DECEMBER 05 - MONDAY DECEMBER 11: AT THE START OF WEEK-2, THERE IS
GOOD AGREEMENT AMONG THE DYNAMICAL MODELS FAVORING ANOMALOUS 500-HPA RIDGING
CENTERED OVER THE ROCKIES WITH DOWNSTREAM TROUGHING OVERSPREADING THE EASTERN
CONUS. AS THIS LATTER MID-LEVEL FEATURE IS FAVORED TO AMPLIFY AND LIFT OUT OVER
EASTERN CANADA, ENSEMBLES DEPICT A MEAN SURFACE LOW WITH THE POTENTIAL TO
RAPIDLY DEEPEN WHILE TRACKING OVER THE NORTHEAST. IN LIGHT OF THIS DEVELOPING
SURFACE FEATURE, THE RISK FOR HEAVY PRECIPITATION EXISTS EARLY NEXT WEEK,
ALTHOUGH THE GEFS AND ECMWF ARE SOMEWHAT DIVIDED ON THE TIMING OF THIS
POTENTIAL. THE ECMWF FAVORS A FASTER SOLUTION OF THE STORM TRACK, PLACING THE
MEAN LOW OVER THE CANADIAN MARITIMES WHEREAS THE GEFS KEEPS THE MEAN LOW
ONSHORE. TO ADDRESS THIS UNCERTAINTY, A SLIGHT RISK OF HEAVY PRECIPITATION IS
ISSUED FOR DAY 8 OVER PARTS OF THE MID-ATLANTIC AND THE NORTHEAST CONSISTENT
WITH THE HIGHEST PRECIPITATION AMOUNTS IN THE UNCALIBRATED GUIDANCE. ALTHOUGH
THE HIGHEST MOISTURE CONTENT IS FAVORED MAINLY EAST OF I-95, ACCUMULATING
SNOWFALL IS POSSIBLE ALONG THE BACKSIDE OF THE DEPARTING SURFACE LOW. GIVEN
SUPPORT FROM THE DETERMINISTIC SOLUTIONS AND THE GEFS SNOW WATER EQUIVALENT
(SWE) PROBABILISTIC EXTREMES TOOL (PET) DEPICTING INCREASED CHANCES FOR AMOUNTS
EXCEEDING THE 85TH PERCENTILE, A SLIGHT RISK OF HEAVY SNOW IS ALSO ISSUED FOR
DEC 5-6 FOR PARTS OF THE GREAT LAKES, APPALACHIANS, AND THE NORTHEAST. THE
FAVORED AMPLIFICATION OF THE TROUGHING ALOFT AND STRENGTHENING PRESSURE
GRADIENTS ALSO SUPPORT A SLIGHT RISK OF HIGH WINDS OVER THE NORTHEASTERN CONUS
FOR DEC 5-6. A MODERATE RISK OF HIGH WINDS WAS CONSIDERED FOR PARTS OF NEW
ENGLAND BASED ON TRENDS IN THE LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE, BUT
THE HIGHEST WINDS ARE EXPECTED TO REMAIN OFFSHORE THUS NO CORRESPONDING HAZARD
IS ISSUED.
UPSTREAM, A DEEP AMPLIFIED 500-HPA TROUGH REMAINS FAVORED OVER THE NORTHEASTERN
PACIFIC, PROMOTING ENHANCED ONSHORE FLOW AND ABOVE-NORMAL PRECIPITATION OVER
MUCH OF THE NORTHWESTERN CONUS. WHILE SOME OF THE HIGHEST PRECIPITATION
AMOUNTS ARE FAVORED LATE IN WEEK-1 (LOCALLY AS MUCH AS 1-3 INCHES FROM TO THE
WEATHER PREDICTION CENTER DAYS 6-7 QPF), THE THREAT OF HEAVY PRECIPITATION IS
FAVORED TO PERSIST INTO EARLY WEEK-2 BASED ON UNCALIBRATED PRECIPITATION
GUIDANCE AND INTEGRATED VAPOR TRANSPORT (IVT) TOOLS WHICH MAINTAIN AN INCREASED
POTENTIAL FOR ATMOSPHERIC RIVER (AR) ACTIVITY DURING THE FIRST FEW DAYS OF THE
PERIOD. A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR DEC 5-7 OVER THE
NORTHERN HALF OF THE WEST COAST WHERE BOTH THE GEFS AND ECWMF PETS INDICATE
20-40% CHANCES FOR PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 2
INCHES OVER THE PACIFIC NORTHWEST (1 INCH OVER NORTHERN CALIFORNIA). WHILE THE
ENHANCEMENT OF PRECIPITATION IS EXPECTED TO BE BENEFICIAL FOR AREAS
EXPERIENCING DROUGHT, ANY HEAVY PRECIPITATION OVER BURN SCARRED AREAS WITHIN
THE HIGHLIGHTED AREA MAY LEAD TO LOCALIZED FLOODING AND/OR DEBRIS FLOWS. GIVEN
THE FAVORED ENHANCEMENT OF TROPOSPHERIC MOISTURE AND SUPPORT FROM THE PETS, A
SLIGHT RISK OF HEAVY SNOW IS POSTED OVER THE HIGHER ELEVATIONS OF THE CASCADES,
INTERMOUNTAIN WEST, NORTHERN ROCKIES, AND PARTS OF THE SIERRA NEVADAS FOR DEC
5-7. BASED ON THE PREVAILING MID-LEVEL AND MEAN SURFACE PATTERN EARLY IN THE
PERIOD, A SLIGHT RISK OF HIGH WINDS IS ISSUED OVER A BROAD AREA OVER THE
WESTERN CONUS. IN ADDITION TO THE LINGERING RISK OF AR ACTIVITY OVER THE
NORTHWESTERN CONUS, AN ELEVATED WIND POTENTIAL EXISTS OVER SOUTHERN CALIFORNIA
WHERE ANOMALOUSLY WARM AND DRIER CONDITIONS ARE EXPECTED WITH STRONG SURFACE
HIGH PRESSURE OVER THE GREAT BASIN TO INDUCE EPISODES OF SANTA ANA WINDS. BY
DAY 10 (DEC 7), ENSEMBLES FAVOR A FAIRLY PROGRESSIVE HEIGHT PATTERN THAT
BECOMES MORE ZONAL WITH TIME, MITIGATING THE RISK OF WEATHER RELATED HAZARDS
OVER THE CONUS FOR THE REMAINDER OF WEEK-2.
TIED TO THE AFOREMENTIONED MID-LEVEL TROUGHING OVER THE NORTHEASTERN PACIFIC,
STRONG SURFACE LOW PRESSURE REMAINS FAVORED OVER THE GULF OF ALASKA, PROLONGING
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 5-7. 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. IN ADDITION, 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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