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FXUS21 KWNC 301849
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 30 2023
SYNOPSIS: POTENTIALLY STRONG SURFACE LOW DEVELOPMENT AND ASSOCIATED FRONTAL
ACTIVITY FAVORED OVER THE EASTERN CONTIGUOUS U.S. (CONUS) FAVORS INCREASED
CHANCES FOR HEAVY PRECIPITATION ACROSS THE EASTERN SEABOARD. IN THE WAKE OF THE
PREDICTED SURFACE LOW, HEAVY LAKE EFFECT SNOW AND MUCH BELOW NORMAL
TEMPERATURES ARE POSSIBLE MAINLY OVER THE GREAT LAKES THROUGH THE MIDDLE OF
WEEK-2. MID-LEVEL LOW PRESSURE OVER THE NORTHEASTERN PACIFIC AND RESULTANT
ENHANCED ONSHORE FLOW MAY BRING HEAVY PRECIPITATION AMOUNTS AND EPISODES OF
HIGH WINDS OVER THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. STRENGTHENING
PRESSURE GRADIENTS ASSOCIATED WITH SURFACE HIGH PRESSURE OVER THE GREAT BASIN
MAY LEAD TO EPISODES OF SANTA ANA WINDS OVER SOUTHERN CALIFORNIA.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR MANY PARTS OF THE EASTERN U.S., TUE-FRI,
NOV 7-10.
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE GREAT LAKES, OHIO VALLEY,
APPALACHIANS, AND THE NORTHEAST, TUE-FRI, NOV 7-10.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE UPPER
MISSISSIPPI VALLEY, GREAT LAKES, AND THE NORTHEAST, WED-SUN, NOV 8-12.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND PARTS OF
NORTHERN CALIFORNIA, TUE-MON, NOV 7-13.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, TUE-MON, NOV 7-13.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF SOUTHERN CALIFORNIA, TUE-SAT, NOV 7-11.
DETAILED SUMMARY
FOR THURSDAY NOVEMBER 02 - MONDAY NOVEMBER 06:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY NOVEMBER 07 - MONDAY NOVEMBER 13: BY EARLY NEXT WEEK, THERE IS GOOD
AGREEMENT IN THE DYNAMICAL MODEL 500-HPA HEIGHT FORECASTS FEATURING AMPLIFIED
TROUGHING OVER THE NORTHEASTERN PACIFIC, WITH DOWNSTREAM RIDGING CENTERED OVER
THE SOUTHWESTERN CONUS AND FALLING MID-LEVEL HEIGHTS EAST OF THE ROCKIES. MUCH
OF THE MID-LEVEL TROUGHING LOOKS TO BECOME MORE AMPLIFIED OVER THE CENTRAL AND
EASTERN U.S. THROUGH THE MIDDLE OF WEEK-2, AS ENSEMBLES ALSO FAVOR A
POTENTIALLY STRONG LOW PRESSURE SYSTEM DEVELOPING OVER THE GREAT PLAINS AND
MISSISSIPPI VALLEY AND TRACKING EASTWARD WITH TIME. WHILE RETURN FLOW AHEAD OF
THE PREDICTED SURFACE LOW LOOKS TO PROVIDE AMPLE MOISTURE AND INCREASE THE RISK
OF HEAVY PRECIPITATION ACROSS THE EASTERN U.S., THE GEFS AND ECMWF ARE SOMEWHAT
SPLIT ON THE POTENTIAL FOR ADDED MOISTURE TIED TO A TROPICAL DISTURBANCE
FAVORED IN THE CARIBBEAN. THE 0Z AND 6Z GEFS ENSEMBLES FEATURE SEVERAL TROPICAL
LOW CENTERS TRACKING NORTHWARD INTO THE EASTERN GULF OF MEXICO AND WESTERN
ATLANTIC, WHEREAS THE 0Z ECMWF ENSEMBLE MAINTAINS A DRIER SOLUTION OVER THE
SOUTHEAST AND LIMITS THE AMOUNT OF TROPICAL MOISTURE AND ACTIVITY TO THE SOUTH.
THESE DIFFERENCES ARE GENERALLY REFLECTED IN THE PROBABILISTIC EXTREMES TOOLS
(PETS) IN TERMS OF THE COVERAGE OF TOTAL PRECIPITATION AMOUNTS IN THE
CALIBRATION, HOWEVER BOTH TOOLS DEPICT AT LEAST 20% CHANCE FOR 3-DAY AMOUNTS
EXCEEDING THE 85TH PERCENTILE OVER THE ENTIRE EASTERN SEABOARD MAINLY EAST OF
THE APPALACHIANS. WITH ELEVATED WET SIGNALS PERSISTING IN THE TOOLS THROUGH THE
MIDDLE OF THE PERIOD, A BROAD SLIGHT RISK AREA OF HEAVY PRECIPITATION IS ISSUED
AND VALID THROUGH NOV 10. IT SHOULD BE NOTED THERE IS STILL A GOOD DEAL OF
UNCERTAINTY IN REGARDS TO IMPACTS FROM TROPICAL ACTIVITY IN THE CARIBBEAN, AND
THIS POTENTIAL WILL CONTINUE TO BE MONITORED AND ADDRESSED IN SUBSEQUENT
OUTLOOKS.
DESPITE MUCH UNCERTAINTY IN REGARDS TO THE DETAILS OF THE STORM TRACK,
ACCUMULATING SNOWFALL IS ALSO FAVORED ON THE BACKSIDE OF THE SURFACE LOW OVER
PARTS OF THE UPPER MIDWEST, GREAT LAKES AND NORTHEAST WHICH IS SUPPORTED IN THE
LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE. THERE ARE MODEST SIGNALS FOR HEAVY
SNOWFALL POTENTIAL IN THE GEFS BASED SNOW WATER EQUIVALENT PET, HOWEVER THE
COMBINATION OF PREVAILING NORTH TO NORTH-WESTERLY FLOW (WITH 850-HPA
TEMPERATURES FAVORED TO DROP INTO THE NEGATIVE TEENS) IN THE WAKE OF THE
DEPARTING SURFACE LOW AND SURFACE LAKE TEMPERATURES REGISTERING UPWARDS OF 50
DEGREES F COULD TRIGGER LOCALLY HEAVY LAKE-EFFECT SNOWFALL FOR THE GREAT LAKES
REGION. THEREFORE, A SLIGHT RISK OF HEAVY SNOW IS ISSUED FOR MUCH OF THE GREAT
LAKES AND FOR PARTS OF THE APPALACHIANS, OHIO VALLEY, AND THE NORTHEAST, FOR
NOV 7-10. IN ADDITION, THE AMPLIFYING TROUGHING ALOFT AND MEAN SURFACE HIGH
PRESSURE DESCENDING FROM SOUTHERN CANADA IS LIKELY TO BRING ANOMALOUSLY COLD
TEMPERATURES AND BELOW-NORMAL WIND CHILLS FOR MANY PARTS OF THE NORTHEASTERN
CONUS. BASED ON THE GEFS AND ECMWF PETS WHICH SHOW INCREASING CHANCES FOR
MINIMUM TEMPERATURE FALLING BELOW THE 15TH PERCENTILE AND 28 DEGREES F (WITH
SOME LOCATIONS BELOW 20 DEGREES F NEAR THE U.S./CANADA BORDER), A SLIGHT RISK
OF MUCH BELOW NORMAL TEMPERATURES IS POSTED FOR NOV 8-12. THESE TOOLS ALSO SHOW
AN INCREASING POTENTIAL FOR SUBFREEZING MINIMUM TEMPERATURES REACHING AS FAR
SOUTH AS THE TENNESSEE VALLEY AND THE SOUTHEAST LATE IN WEEK-2. HOWEVER, NO
CORRESPONDING HAZARD COVERAGE IS POSTED DUE TO GENERAL UNCERTAINTY AT THIS LEAD
AND WHETHER SUCH TEMPERATURES WOULD BE IMPACTFUL ON VEGETATION GIVEN THE COLD
AIR OUTBREAK FAVORED OVER THIS PART OF THE COUNTRY DURING WEEK-1.
UPSTREAM, THE GEFS AND ECMWF CONTINUE TO SHOW SIGNS OF ANOMALOUS MID-LEVEL
TROUGHING ENCROACHING WESTERN NORTH AMERICA TO PROMOTE ENHANCED ONSHORE FLOW
ABOVE-NORMAL PRECIPITATION OVER THE NORTHWESTERN CONUS. WHILE THERE ARE
DIFFERENCES BETWEEN THE GEFS AND ECMWF IN REGARDS TO THE MAGNITUDE OF
ATMOSPHERIC RIVER (AR) POTENTIAL IN THE INTEGRATED VAPOR TRANSPORT (IVT) TOOLS,
GOOD TEMPORAL AGREEMENT EXISTS WHICH SHOW A BRIEF PAUSE OF ENHANCED MOISTURE
FLOW EARLY IN WEEK-2, FOLLOWED BY AN UPTICK IN AR POTENTIAL THE PERSISTS
THROUGHOUT THE REMAINDER OF THE PERIOD. GIVEN GOOD SUPPORT IN THE PETS
INDICATING AT LEAST A 20% CHANCE FOR 3-DAY AMOUNTS EXCEEDING THE 85TH
PERCENTILE WITH SIMILAR CHANCES FOR 1.5 TO 2 INCHES, A SLIGHT RISK OF HEAVY
PRECIPITATION IS POSTED FOR NOV 7-13. A SLIGHT RISK OF HIGH WINDS ALSO REMAINS
POSTED FOR THE ENTIRETY OF WEEK-2 BASED ON PETS ALSO INDICATING INCREASED
CHANCES FOR WIND SPEEDS EXCEEDING THE 85TH PERCENTILE. THE EXCESS IN MOISTURE
IS LIKELY TO PRODUCE ACCUMULATING SNOWFALL IN THE HIGHER ELEVATIONS OF THE
CASCADES AND PORTIONS OF THE NORTHERN ROCKIES, THOUGH TOTALS APPEAR UNLIKELY TO
REACH HAZARD THRESHOLDS.
TIED TO THE ANOMALOUS RIDGING FAVORED FURTHER SOUTH, CONDITIONS ARE EXPECTED TO
REMAIN ANOMALOUSLY HOT AND DRY OVER SOUTHERN CALIFORNIA, THE SOUTHWEST AND
LOWER FOUR CORNERS. WITH MODELS FAVORING MORE MEAN SURFACE HIGH PRESSURE OVER
THE WESTERN GREAT BASIN, THERE IS AN INCREASED POTENTIAL FOR EPISODES OF SANTA
ANA WINDS OVER SOUTHERN CALIFORNIA AND A SLIGHT RISK OF HIGH WINDS IS POSTED
FOR NOV 7-11.
OVER ALASKA, AMPLIFIED RIDGING CENTERED TO THE SOUTH OF THE ALEUTIANS AND MORE
NORTHERLY FLOW FROM THE BERING SEA IS LIKELY TO BRING NEAR TO BELOW NORMAL
TEMPERATURES FOR MUCH OF THE MAINLAND. THE LARGEST NEGATIVE TEMPERATURE
DEPARTURES ARE FAVORED OVER THE SEWARD PENINSULA AND PARTS OF THE NORTHERN
SLOPE, THOUGH ACTUAL TEMPERATURES ARE NOT EXPECTED TO REACH HAZARD THRESHOLDS.
WITH INCREASED ONSHORE FLOW DOWNSTREAM OF THE MID-LEVEL RIDGE, ABOVE-NORMAL
PRECIPITATION AND HIGH WINDS ARE ALSO FAVORED OVER THE SOUTHEAST, BUT
CONDITIONS ARE NOT EXPECTED TO BE HAZARDOUS.
FORECASTER: NICK NOVELLA
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