097
FXUS21 KWNC 271801
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 27 2023
SYNOPSIS: A STRONG UPPER-LEVEL JET EXTENDING FROM THE NORTHEASTERN PACIFIC AND
ENHANCED ONSHORE FLOW FAVORED OVER THE NORTHWESTERN CONTIGUOUS U.S. (CONUS)
ELEVATES CHANCES FOR HEAVY PRECIPITATION AND HIGH WINDS OVER PARTS OF THE
PACIFIC NORTHWEST. MID-LEVEL LOW PRESSURE OVER CANADA AND PERSISTENT
NORTHWESTERLY FLOW INCREASES THE RISK FOR MUCH BELOW NORMAL TEMPERATURES OVER
PARTS OF THE NORTH-CENTRAL CONUS. INCREASED TROPICAL MOISTURE FROM THE
CARIBBEAN MAY LEAD TO LOCALLY HEAVY PRECIPITATION OVER PARTS OF THE SOUTHEAST.
HAZARDS
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES OVER PARTS OF THE NORTHERN PLAINS
AND UPPER MISSISSIPPI VALLEY, SAT-WED, NOV 4-8.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND PARTS OF
NORTHERN CALIFORNIA, SAT-WED, NOV 4-8.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA, SAT-WED, NOV 4-8.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHEAST, SAT-TUE, NOV
4-7.
DETAILED SUMMARY
FOR MONDAY OCTOBER 30 - FRIDAY NOVEMBER 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY NOVEMBER 04 - FRIDAY NOVEMBER 10: FOLLOWING THE PASSAGE OF A DEEP
500-HPA TROUGH THAT IS EXPECTED TO INDUCE A SHOT OF ARCTIC AIR THROUGHOUT THE
CENTRAL AND EASTERN CONUS DURING WEEK-1, THERE IS GOOD CONTINUITY IN THE
DYNAMICAL MODELS FEATURING BUILDING MID-LEVEL HEIGHTS AND ANOMALOUS RIDGING
OVERSPREADING MUCH OF THE LOWER 48 BY NEXT WEEKEND. THE PATTERN TRANSITION IS
EXPECTED TO LEAD TO A MODERATION OF TEMPERATURES FOR MANY AREAS AFFECTED BY
POTENTIALLY HAZARDOUS COLD NEXT WEEK, WHILE MAINTAINING UNSEASONABLY WARM
CONDITIONS THROUGHOUT MANY PARTS OF THE WEST DURING THE WEEK-2 PERIOD. ONE
EXCEPTION LIES OVER THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY, WHERE
BOTH THE TEMPERATURE TOOLS MAINTAIN A FAIRLY PERSISTENT COLD SIGNAL LIKELY
ASSOCIATED WITH ANOMALOUS TROUGHING FAVORED OVER THE HUDSON BAY PROMOTING
NORTHWESTERLY FLOW INTO THE NORTH-CENTRAL CONUS. IN CONSIDERATION OF POSITIVE
FEEDBACK EFFECTS WITH ABOVE-NORMAL SNOWPACK IN THIS PART OF THE COUNTRY AND
SOME SUPPORT IN THE RAW TEMPERATURE GUIDANCE, A SLIGHT RISK OF MUCH BELOW
NORMAL TEMPERATURES IS POSTED (NOV 4-8) OVER PARTS OF EASTERN MONTANA, THE
DAKOTAS, AND MINNESOTA WHERE BOTH THE GEFS AND ECMWF PROBABILISTIC EXTREMES
TOOLS (PET) SHOW 20-30% CHANCES FOR MINIMUM TEMPERATURES FALLING BELOW THE 15TH
PERCENTILE AND BELOW 20 DEGREES F. LATER IN WEEK-2, 500-HPA HEIGHT FORECASTS
DEPICT ANOMALOUS TROUGHING POTENTIALLY REDEVELOPING OVER THE EASTERN U.S TO
HELP USHER THE RETURN OF BELOW-NORMAL TEMPERATURES SPREADING EASTWARD, BUT
GIVEN GENERAL UNCERTAINTY AT THIS LEAD AND MODEST SIGNALS IN THE PETS, NO
TEMPERATURE HAZARDS ARE POSTED.
UPSTREAM, THERE ARE CONTINUED SIGNS OF A STRONG UPPER-LEVEL JET OVER THE
EASTERN PACIFIC WITH ENHANCED ONSHORE FLOW TO PROMOTE ABOVE-NORMAL
PRECIPITATION OVER THE NORTHERN WEST COAST. WHILE THE GEFS BASED PRECIPITATION
TOOLS HAVE GROWN SLIGHTLY WETTER COMPARED TO YESTERDAY, THERE IS A CONSIDERABLE
REDUCTION IN HEAVY PRECIPITATION SIGNALS FROM BOTH THE RAW AND CALIBRATED ECMWF
TOOLS WHICH IS LIKELY TIED TO POSITIVE MID-LEVEL HEIGHT DEPARTURES NOW FAVORED
IN THE MODEL OVER THE PACIFIC NORTHWEST. AS A RESULT OF THE LOWERED
PRECIPITATION AMOUNTS FAVORED, THE MODERATE RISK OF HEAVY PRECIPITATION IS
REMOVED FROM TODAY'S OUTLOOK, BUT A CORRESPONDING SLIGHT RISK AREA REMAINS
VALID OVER THE PACIFIC NORTHWEST AND PARTS OF NORTHERN CALIFORNIA THROUGH NOV
8. WITHIN THE HIGHLIGHTED REGION, THERE IS GOOD AGREEMENT BETWEEN THE GEFS AND
ECMWF 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 HIGH
WINDS ALSO REMAINS POSTED GIVEN CONTINUED SUPPORT FROM THE PETS AND ELEVATED
SIGNALS IN THE INTEGRATED VAPOR TRANSPORT TOOL (IVT) FOR POSSIBLE ATMOSPHERIC
RIVER ACTIVITY. 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.
ACROSS THE TROPICS, DYNAMICAL MODELS CONTINUE TO FAVOR THE EMERGENCE OF A
CENTRAL AMERICA 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 NATIONAL HURRICANE
CENTER (NHC) IS CURRENTLY MONITORING AN AREA IN THE CARIBBEAN WHERE A BROAD
AREA OF LOW PRESSURE IS EXPECTED TO FORM DURING THE NEXT FEW DAYS, WITH 30%
CHANCES OF TC DEVELOPMENT DURING THE NEXT WEEK. AS THE MEAN LOW IS FAVORED TO
MOVE GENERALLY NORTHWARD, THERE IS AN INCREASE IN TROPICAL MOISTURE AND
PRECIPITATION AMOUNTS EVIDENT IN THE ENSEMBLES OFF THE COAST OF THE
SOUTHEASTERN CONUS LATE IN WEEK-1 AND INTO WEEK-2. THE GEFS AND ECMWF PETS
REFLECT THIS ENHANCEMENT OF MOISTURE FROM THE CARIBBEAN, DEPICTING INCREASED
CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE, WITH THE LATTER TOOL
INDICATING AT LEAST A 20% CHANCES FOR AMOUNTS EXCEEDING 1 INCH ACROSS THE LOWER
EASTERN SEABOARD. REGARDLESS OF ANY TC ACTIVITY, THE INCREASE IN MOISTURE ALONG
A PREDICTED STALLED FRONTAL BOUNDARY AND CYCLONIC SURFACE FLOW FAVORED JUST
OFFSHORE SUPPORTS A SLIGHT RISK OF HEAVY PRECIPITATION FOR THE SOUTHEAST FOR
NOV 4-7.
OVER ALASKA, ABOVE- (BELOW-) NORMAL TEMPERATURES (PRECIPITATION) ARE
PREDOMINATELY FAVORED THROUGHOUT MUCH OF THE STATE ASSOCIATED WITH ANOMALOUS
MID-LEVEL RIDGING FORECAST OVER THE MAINLAND. AS THIS RIDGING IS FAVORED TO
WEAKEN, A TRANSITION TO MORE ZONAL OR NORTHERLY FLOW IS EXPECTED TO LEAD TO
COOLING TEMPERATURES, THOUGH MINIMUM TEMPERATURES ARE EXPECTED TO REMAIN WELL
ABOVE HAZARD THRESHOLDS.
FORECASTER: NICK NOVELLA
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