639
FXUS21 KWNC 051926
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 05 2024
SYNOPSIS: EARLY IN WEEK-2, SURFACE LOW FORMATION FAVORED IN THE LEE OF THE
ROCKIES IS EXPECTED TO BRING ANOTHER ROUND OF INCREASED, AND POSSIBLY HEAVY
PRECIPITATION, ALONG WITH AN INCREASED RISK FOR A PERIOD OF HIGH WINDS FOR MANY
PARTS OF THE CENTRAL AND EASTERN CONTIGUOUS U.S. UPSTREAM, THE FAVORED RETURN
OF MID-LEVEL LOW PRESSURE AND ENHANCED ONSHORE FLOW MAY LEAD TO HEAVY
PRECIPITATION AND HIGH ELEVATION SNOWFALL ACROSS THE PACIFIC NORTHWEST, AS WELL
AS AN INCREASED RISK OF HEAVY SNOW AND EPISODES OF HIGH WINDS FOR MANY PARTS OF
THE INTERIOR WEST LATER IN WEEK-2. UNSETTLED WEATHER MAY RETURN TO PARTS OF
WESTERN ALASKA FOLLOWING A BRIEF LULL IN ACTIVITY EARLY IN WEEK-2.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, MIDDLE AND LOWER MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS, AND THE
SOUTHEAST, WED-FRI, NOV 13-15.
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF GREAT PLAINS, MISSISSIPPI,
TENNESSEE AND OHIO VALLEYS, APPALACHIANS, MID-ATLANTIC, AND NORTHEAST, WED-FRI,
NOV 13-15.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST,
WED-FRI, NOV 13-15.
SLIGHT RISK OF HEAVY SNOW ACROSS NORTHERN PORTIONS OF THE CASCADES, WED-FRI,
NOV 13-15.
SLIGHT RISK OF HEAVY SNOW ACROSS MANY PORTIONS OF THE ROCKIES, WED-TUE, NOV
13-19.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WESTERN CONUS, AND CENTRAL AND
NORTHERN HIGH PLAINS, WED-SUN, NOV 13-17.
SLIGHT RISK OF HIGH WINDS ACROSS COASTAL PORTIONS OF SOUTHWESTERN MAINLAND
ALASKA AND THE ALEUTIANS, THU-SAT, NOV 14-16.
DETAILED SUMMARY
FOR FRIDAY NOVEMBER 08 - TUESDAY NOVEMBER 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY NOVEMBER 13 - TUESDAY NOVEMBER 19: BY THE OUTSET OF WEEK-2, THERE
IS FAIR AGREEMENT AMONG THE DYNAMICAL MODELS FAVORING AMPLIFIED 500-HPA
SHORTWAVE TROUGHING SHIFTING FROM THE INTERIOR WEST INTO THE GREAT PLAINS, WITH
POTENT MID-LEVEL RIDGING ESTABLISHED OVER MUCH OF EASTERN NORTH AMERICA. FOR
WHAT APPEARS TO BE A RECURRING THEME SINCE THE START OF NOVEMBER ACROSS THE
CENTRAL CONUS (FOLLOWING A VERY DRY OCTOBER), THE FAVORED SYNOPTIC SETUP TIED
TO THESE FEATURES ALOFT, CONSISTING OF SURFACE LOW FORMATION IN THE LEE OF THE
ROCKIES WITH ENHANCED MOISTURE ADVECTION IN THE WARM SECTOR, REMAINS SUPPORTIVE
FOR ABOVE-NORMAL AND POTENTIALLY HEAVY PRECIPITATION ACCUMULATIONS EAST OF THE
ROCKIES TOWARDS THE MIDDLE OF NEXT WEEK. HOWEVER, DIFFERENCES EXIST IN REGARDS
TO THE MID-LEVEL PATTERN UPSTREAM WITH THE GEFS AND CANADIAN LOOKING EAGER TO
RELOAD THE TROUGHING OVER THE PACIFIC NORTHWEST, AND THE ECMWF BEING MORE OF AN
OUTLIER IN BUILDING A TRANSIENT RIDGE OVER THE WEST COAST. AS A RESULT, THERE
ARE NOT ONLY UNCERTAINTIES IN REGARDS TO THE TIMING OF ENHANCED ONSHORE FLOW
RETURNING OVER THE WEST COAST, BUT ALSO IN REGARDS TO THE STRENGTH AND
PLACEMENT OF ANOMALOUS COLD AIR BEING ADVECTED EASTWARD BEHIND THE PREDICTED
FRONTAL SYSTEM TO PROVIDE THE POINT OF STRONGEST FORCING FOR HEAVY
PRECIPITATION DOWNSTREAM.
ACROSS THE CENTRAL AND EASTERN CONUS, BOTH THE RAW PRECIPITATION GUIDANCE AND
PROBABILISTIC EXTREME TOOLS (PETS) ARE REFLECTIVE OF THESE DIFFERENCES, WITH
THE GEFS (ECMWF) FAVORING A MORE NORTHERLY (SOUTHERLY) MEAN SOLUTION OF THE
HEAVY PRECIPITATION POTENTIAL EARLY IN THE PERIOD. ALTHOUGH ELEVATED CHANCES
(>40%) ARE FEATURED IN THE UNCALIBRATED ECMWF TOOL TO SUPPORT THE ADDITION OF A
MODERATE RISK, BOTH THE GENERAL MISLOCATION AND RELATIVELY WEAKER HEAVY
PRECIPITATION SIGNALS IN THE GEFS AND CANADIAN PRECLUDES THIS DESIGNATION.
THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION REMAINS ISSUED (NOV 13-15) FROM
THE SOUTHERN PLAINS TO THE SOUTHERN APPALACHIANS WHERE THE GEFS AND ECWMF PETS
SHOW THE GREATEST AGREEMENT DEPICTING INCREASED CHANCES FOR 3-DAY AMOUNTS
EXCEEDING THE 85TH PERCENTILE AND 1 INCH EARLY IN THE PERIOD. IT IS WORTH
NOTING THAT THUNDERSTORM ACTIVITY IS ALSO POSSIBLE WITHIN THE HIGHLIGHTED
SLIGHT RISK AREA, PARTICULARLY IF ANY SHARP TEMPERATURE AND MOISTURE GRADIENTS
TAKE SHAPE IN THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY AS ALLUDED BY
THE ECMWF ENSEMBLE. IN ADDITION, ENSEMBLES SUGGEST STRENGTHENING PRESSURE
GRADIENTS ARE POSSIBLE ALONG THE PREDICTED FRONTAL SYSTEM. ALTHOUGH THERE
REMAINS UNCERTAINTY WITH THE DETAILS OF THE EVENTUAL STORM TRACK, THERE IS
BETTER SUPPORT IN THE PETS FAVORING A BROAD AREA OF INCREASED CHANCES FOR WIND
SPEEDS EXCEEDING THE 85TH PERCENTILE EARLY IN WEEK-2 TIED TO THE SURFACE
FEATURE, AND A SLIGHT RISK OF HIGH WINDS IS ISSUED FOR NOV 13-15. AS THE
SHORTWAVE TROUGHING SHIFTS EASTWARD, HEAVY PRECIPITATION IS POSSIBLE OVER THE
MID-ATLANTIC AND NORTHEAST BY DAYS 9 AND 10 (NOV 14-15), BUT DUE TO THE LACK OF
SUPPORT IN THE GEFS TOOLS, THE SLIGHT RISK COVERAGE REMAINS UNCHANGED. ANY
INCREASED PRECIPITATION AMOUNTS WOULD ALSO BRING WELCOMED GROUND MOISTURE FOR
MANY AREAS ALONG THE EAST COAST, PARTICULARLY FOR THE NORTHEAST WHERE MODERATE
AND SEVERE DROUGHT (D1 TO D2) CONDITIONS ARE CURRENTLY BEING REGISTERED.
DESPITE SOME OF THE AFOREMENTIONED DIFFERENCES IN THE TIMING OF THE MEAN TROUGH
RELOADING OVER THE WEST COAST AMONG THE MODELS, THE FAVORED RETURN OF ENHANCED
ONSHORE FLOW SUPPORTS THE CONTINUATION OF SLIGHT RISK OF HEAVY PRECIPITATION
OVER THE PACIFIC NORTHWEST, AND AN ACCOMPANYING SLIGHT RISK OF HIGH ELEVATION
HEAVY SNOW OVER PORTIONS OF THE CASCADES FOR NOV 13-15. BOTH THE GEFS AND ECMWF
PETS SHOW AT LEAST 20% CHANCES OF 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE,
WITH POCKETS OF OVER 2 INCHES THROUGH DAY 10 (NOV 15). BEYOND THIS TIME, MANY
SHORTWAVE MID-LEVEL FEATURES BECOME LOST IN THE ENSEMBLE MEANS AT LONGER LEADS,
BUT ALL MODELS MAINTAIN A MEAN TROUGH COVERING MUCH OF THE WEST FOR THE
REMAINDER OF WEEK-2. THE COMBINATION OF CONTINUED PACIFIC MOISTURE ADVECTION
WITH CYCLONIC FLOW ALOFT OVER THE HIGHER ELEVATIONS IS EXPECTED TO BE CONDUCIVE
FOR PERIODS OF POTENTIALLY HEAVY SNOW OVER THE ROCKIES, AND A CORRESPONDING
SLIGHT RISK AREA IS MAINTAINED IN THE UPDATED OUTLOOK FOR ALL OF WEEK-2. FOR
WINDS, THERE APPEARS TO BE LESS AGREEMENT IN THE PETS RELATIVE TO PREVIOUS
GUIDANCE, HOWEVER A BROAD SLIGHT RISK AREA IS POSTED FOR MUCH OF THE WEST AND
EXTENDING INTO THE HIGH PLAINS (NOV 13-17) GIVEN THE POTENTIAL FOR AN
AMPLIFYING LONG-WAVE TROUGH THROUGH THE MIDDLE OF WEEK-2.
ACROSS THE TROPICS, THE ENHANCED PHASE OF A ROBUST MADDEN-JULIAN OSCILLATION
(MJO) LIKELY CONTRIBUTED TO THE FORMATION OF TROPICAL STORM RAFAEL IN THE
SOUTHERN CARIBBEAN. BASED ON THE LATEST NATIONAL HURRICANE CENTER'S (NHC)
OFFICIAL FORECAST TRACK, WHICH PLACES A WEAKENING LOW OVER THE CENTRAL GULF OF
MEXICO BY THIS WEEKEND, MUCH OF THE HEAVY PRECIPITATION TIED TO RAFAEL IS
EXPECTED TO TIME OFF WELL BEFORE THE START OF WEEK-2. HOWEVER, SEVERAL
SOLUTIONS FROM THE ECMWF SHOW A SLOWER TRACK INTO THE WESTERN GULF WHERE ANY
TROPICAL MOISTURE FROM A REMNANT CIRCULATION COULD POSSIBLY LINGER AND SPREAD
INTO THE SOUTHERN U.S. TOWARDS THE MIDDLE OF NEXT WEEK. THIS, IN PART, MAY
EXPLAIN SOME OF THE STRONGER PRECIPITATION SIGNALS FAVORED IN THE ECMWF
GUIDANCE EARLY IN WEEK-2. THERE IS LITTLE CONFIDENCE FOR THIS REALIZATION, BUT
THE SITUATION BEARS MONITORING.
IN THE WAKE OF A DEPARTING SHORTWAVE TROUGH NEXT WEEK, ANOMALOUS 500-HPA
RIDGING IS FAVORED TO DEVELOP OVER THE NORTHEASTERN PACIFIC TO BRING MORE
TRANQUIL CONDITIONS TOWARDS THE MIDDLE OF NEXT WEEK. HOWEVER, ENSEMBLES
CONTINUE TO SHOW ADDITIONAL TROUGH AND SURFACE LOW PRESSURE OVER THE BERING
SEA, WHICH MAY BRING ANOTHER PERIOD OF STRONG PRESSURE GRADIENTS OVER THE
ALEUTIANS AND THE SOUTHWESTERN MAINLAND BY DAY 9 (NOV 14). BASED ON CONTINUED
SUPPORT IN THE PETS, A SLIGHT RISK OF HIGH WINDS REMAINS POSTED FOR THESE
REGIONS FOR NOV 14-16.
FORECASTER: NICK NOVELLA
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