131
FXUS21 KWNC 261822
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 26 2023
SYNOPSIS: EARLY IN WEEK-2, STRONG MEAN SURFACE HIGH PRESSURE ASSOCIATED WITH AN
ARCTIC AIR MASS IS FAVORED TO LINGER ACROSS THE EAST-CENTRAL CONTIGUOUS U.S.
(CONUS), LEADING TO SLIGHT CHANCES FOR MUCH BELOW NORMAL MINIMUM TEMPERATURES
LATE NEXT WEEK BEFORE A WARMING TREND IS FAVORED FOR THE REMAINDER OF THE
PERIOD. A STRONG UPPER-LEVEL JET EXTENDING FROM THE EASTERN PACIFIC AND
ENHANCED ONSHORE FLOW FAVORED OVER THE NORTHWESTERN CONUS ELEVATES CHANCES FOR
HEAVY PRECIPITATION AND HIGH WINDS OVER PARTS OF THE PACIFIC NORTHWEST. ACROSS
THE TROPICS, CONDITIONS APPEAR CONDUCIVE FOR POTENTIAL TROPICAL CYCLONE
DEVELOPMENT IN THE CARIBBEAN, HOWEVER LARGE ENSEMBLE SPREAD AND PRECIPITATION
TOOLS REMAIN GENERALLY UNSUPPORTIVE OF ANY PRECIPITATION OR WIND RELATED
HAZARDS OVER THE SOUTHERN U.S. AT THIS TIME.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION FOR PARTS OF THE PACIFIC NORTHWEST,
FRI-SUN, NOV 3-5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND PARTS OF
NORTHERN CALIFORNIA, FRI-TUE, NOV 3-7.
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE MISSISSIPPI,
TENNESSEE AND OHIO VALLEYS, SOUTHEAST, APPALACHIANS, AND THE MID-ATLANTIC, FRI,
NOV 3.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, FRI-TUE, NOV 3-7.
DETAILED SUMMARY
FOR SUNDAY OCTOBER 29 - THURSDAY NOVEMBER 02:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY NOVEMBER 03 - THURSDAY NOVEMBER 09: BY THE MIDDLE OF NEXT WEEK, DEEP
500-HPA TROUGHING AND AN ACCOMPANYING ARCTIC AIR MASS OVER THE CENTRAL AND
EASTERN CONUS LOOKS TO BE EXPIRING TOWARDS THE OUTSET OF THE WEEK-2 PERIOD.
BOTH THE GEFS AND ECMWF FAVOR BUILDING MID-LEVEL HEIGHTS TO THE EAST OF ROCKIES
SUPPORTIVE OF MODERATING TEMPERATURES, THOUGH STRONG SURFACE HIGH PRESSURE
REMAINS CENTERED OVER THE MID-ATLANTIC IN THE RAW ENSEMBLE GUIDANCE, WHERE
CONCERNS FOR HAZARDOUSLY COLD MINIMUM TEMPERATURES ARE EXPECTED TO LINGER.
CONSISTENT WITH PREVIOUS CALIBRATED GUIDANCE, LARGE DIFFERENCES EXIST BETWEEN
THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS), AS THE LATTER REMAINS
MORE PRONOUNCED IN REGARDS TO HAZARD POTENTIAL TIED TO THE PASSAGE OF THE
PREDICTED COLD AIR MASS. HOWEVER, THERE IS FAIR AGREEMENT IN THE RAW
TEMPERATURE TOOLS ALONG WITH INCREASED CHANCES FOR SUBFREEZING TEMPERATURES IN
THE PETS FROM THE OHIO AND TENNESSEE VALLEYS TO THE COASTAL MID-ATLANTIC IN THE
PETS TO SUPPORT A SLIGHT RISK OF MUCH BELOW TEMPERATURES FOR DAY 8 (NOV 3).
MANY OF THESE AREAS IN THE HIGHLIGHTED REGION LOOK TO EXPERIENCE THEIR FIRST
FREEZE OF THE SEASON WHICH IS LIKELY TO AFFECT VULNERABLE VEGETATION.
COMPARED TO YESTERDAY, A STRONGER UPPER-LEVEL JET OVER IS FEATURED IN BOTH THE
GEFS AND ECMWF ENSEMBLES OVER THE NORTHEASTERN PACIFIC, WHICH IS LIKELY TO
BRING ENHANCED ONSHORE FLOW AND POSSIBLE ATMOSPHERIC RIVER (AR) ACTIVITY OVER
THE NORTHWESTERN CONUS. THE ECMWF HAS BECOME MORE ROBUST IN REGARDS TO HEAVY
PRECIPITATION POTENTIAL IN BOTH THE INTEGRATED VAPOR TRANSPORT (IVT) TOOL AND
CALIBRATED PRECIPITATION GUIDANCE, WHERE ELEVATED CHANCES (50-60%) FOR 3-DAY
ACCUMULATIONS EXCEEDING THE 85TH PERCENTILE ARE EVIDENT IN THE ECMWF PET EARLY
IN THE PERIOD. WHILE THE GEFS FAVORS LESSER CHANCES IN PERCENTILE SPACE AND IS
COMPARABLY DRIER WITH THE RAW AMOUNTS, THE GEFS, ECMWF AND CANADIAN HAVE BEEN
TRENDING WETTER IN RECENT DAYS, ADDING CONFIDENCE IN THE HAZARDOUS
PRECIPITATION RISK. BASED ON THE UNCALIBRATED ECMWF INDICATING 40-50% CHANCES
FOR 3-DAY AMOUNTS EXCEEDING 2 INCHES, A MODERATE RISK OF HEAVY PRECIPITATION IS
ISSUED FOR PARTS OF WESTERN OREGON AND WASHINGTON FOR NOV 3-5. GIVEN THE
PERSISTENCE OF WET SIGNALS IN THE TOOLS, A BROADER SLIGHT RISK AREA OF HEAVY
PRECIPITATION REMAINS ISSUED EXTENDING SOUTHWARD INTO NORTHERN CALIFORNIA, AND
IS VALID THROUGH DAY 12 (NOV 7). THE EXCESS IN MOISTURE IS LIKELY TO PRODUCE
ACCUMULATING SNOWFALL IN THE HIGHER ELEVATIONS OF THE CASCADES, THOUGH TOTALS
APPEAR UNLIKELY TO REACH HAZARD THRESHOLDS. HOWEVER, THE INCREASED POTENTIAL
FOR AR ACTIVITY PROMPTS A SLIGHT RISK OF HIGH WINDS (NOV 3-7) MAINLY OVER THE
PACIFIC NORTHWEST, WHICH IS ALSO SUPPORTED IN THE GEFS AND ECMWF PETS DEPICTING
WIND SPEEDS EXCEEDING THE 85TH PERCENTILE THROUGH THE MIDDLE OF THE PERIOD.
ACROSS THE TROPICS, DYNAMICAL MODELS CONTINUE TO FAVOR THE EMERGENCE OF A
CENTRAL AMERICAN GYRE (CAG), WHERE THE BROAD SCALE CYCLONIC CIRCULATION AND
DECREASED WIND SHEAR REMAINS FAVORABLE FOR TROPICAL CYCLONE (TC) FORMATION
TOWARDS THE END OF OCTOBER AND INTO EARLY NOVEMBER. THE INCREASED POTENTIAL IS
REFLECTED IN THE PROBABILISTIC TC GENESIS TOOLS, AND THE ECMWF PET DEPICTS
INCREASING CHANCES OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE
OVER THE GULF COAST STATES SUGGESTIVE OF TROPICAL MOISTURE SHIFTING NORTHWARD
FROM THE CARIBBEAN THROUGH THE MIDDLE OF PERIOD. HOWEVER, THERE IS STILL A GOOD
DEAL OF SPREAD IN THE GEFS AND ECMWF ENSEMBLES AND THE DAILY RAW PRECIPITATION
TOOLS GENERALLY REMAIN UNSUPPORTIVE OF A HEAVY PRECIPITATION RISK, RESULTING IN
NO CORRESPONDING HAZARD BEING POSTED AT THIS TIME. POTENTIAL TROPICAL IMPACTS
WILL CONTINUE TO BE MONITORED IN SUBSEQUENT OUTLOOKS.
OVER ALASKA, ABOVE- (BELOW-) NORMAL TEMPERATURES (PRECIPITATION) ARE
PREDOMINATELY FAVORED THROUGHOUT MUCH OF THE STATE ASSOCIATED WITH ANOMALOUS
MID-LEVEL RIDGING FORECAST THROUGH THE START OF NOVEMBER. BEYOND THIS TIME,
MODELS SHOW THIS MID-LEVEL FEATURE WEAKENING WITH A TRANSITION TO MORE
NORTHERLY FLOW TO HELP BRING COLDER TEMPERATURES PARTICULARLY OVER THE WESTERN
MAINLAND TOWARDS THE END OF WEEK-2. THE COOLING TREND IS REFLECTED IN THE PET
GUIDANCE, BUT NO HAZARDS AS TEMPERATURES AREN'T EXPECTED TO REACH HAZARD
THRESHOLDS AND GENERAL UNCERTAINTY AT THIS LEAD.
FORECASTER: NICK NOVELLA
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