970
FXUS21 KWNC 031745
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT NOVEMBER 03 2023
SYNOPSIS: A FAST, PROGRESSIVE FLOW PATTERN IS FORECAST OVER NORTH AMERICA
DURING MID-NOVEMBER. THE MOST PERSISTENT MID-LEVEL FEATURE IS AN AREA OF
MID-LEVEL LOW PRESSURE OFFSHORE OF THE WEST COAST. PERIODS OF ENHANCED ONSHORE
FLOW ASSOCIATED WITH THIS FEATURE SLIGHTLY ELEVATES THE CHANCE FOR HEAVY
PRECIPITATION AND HIGH WINDS ACROSS THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA. THERE ARE SIGNS THAT THE SOUTHERN TIER OF THE CONTIGUOUS U.S.
(CONUS) COULD BECOME WETTER BY MID-NOVEMBER WITH THE WEEK-2 OUTLOOK FAVORING
ABOVE-NORMAL PRECIPITATION ACROSS PORTIONS OF THE SOUTH-CENTRAL AND
SOUTHEASTERN CONUS, WITH SURFACE HIGH PRESSURE FAVORING A DRY PATTERN ACROSS
THE NORTHERN TIER.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, SAT-WED, NOV 11-15.
SLIGHT RISK OF EPISODES OF HIGH WINDS OVER COASTAL PARTS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, SAT-WED, NOV 11-15.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN PLAINS, MIDDLE AND
LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND SOUTHEAST, SAT-WED, NOV 11-15.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHEAST,
SAT-MON, NOV 11-13.
DETAILED SUMMARY
FOR MONDAY NOVEMBER 06 - FRIDAY NOVEMBER 10:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY NOVEMBER 11 - FRIDAY NOVEMBER 17: A SERIES OF SHORTWAVE TROUGHS
ARE FORECAST TO PROGRESS ACROSS THE EASTERN PACIFIC AND INTO THE WEST COAST OF
THE CONUS DURING WEEK-2. EACH OF THESE SYSTEMS HAS THE POTENTIAL TO BRING
ROUNDS OF HEAVY PRECIPITATION AND HIGH WINDS TO PARTS OF THE PACIFIC NORTHWEST
AND NORTHERN CALIFORNIA. THE GEFS PROBABILISTIC EXTREMES TOOL (PET) KEEPS
PROBABILITIES FOR 3-DAY PRECIPITATION REACHING THE 85TH CLIMATOLOGICAL
PERCENTILE UNDER 20 PERCENT THROUGHOUT WEEK-2 ALONG MOST OF THE WEST COAST.
HOWEVER, THE ECMWF PET CONTINUES TO DEPICT PROBABILITIES GREATER THAN 20
PERCENT THROUGH DAY-12 FROM NORTHERN CALIFORNIA NORTHWARD THROUGH WESTERN
OREGON AND WASHINGTON, WITH INCREASED CHANCES FOR 3-DAY PRECIPITATION TOTALS
EXCEEDING 1 TO 1.5 INCHES. THERE IS ALSO SUBSTANTIAL VARIATION BETWEEN THE 0Z
GEFS AND THE ECMWF ENSEMBLES ON THE TIMING OF ROUNDS OF HEAVY PRECIPITATION.
DUE TO THE CONTINUED ELEVATED HAZARDOUS PRECIPITATION SIGNAL IN THE ECMWF PET,
AND FOR CONTINUITY, THE SLIGHT RISK FOR HEAVY PRECIPITATION REMAINS IN PLACE
ACROSS PARTS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA, NOV 11-15,
ALTHOUGH SIGNALS ARE MORE MARGINAL COMPARED TO PREVIOUS OUTLOOKS. A CONCURRENT
SLIGHT RISK OF EPISODES OF HIGH WINDS ALSO REMAINS IN PLACE OVER THE SAME
AREAS. ALTHOUGH ACCUMULATING SNOW IS EXPECTED AT THE HIGHER ELEVATIONS OF THE
CASCADES AND AS FAR SOUTH AS THE NORTHERN SIERRA NEVADA MOUNTAINS, HEAVY
SNOWFALL AMOUNTS ARE NOT ANTICIPATED WITH RELATIVELY HIGH SNOW LEVELS
PRECLUDING A RELATED HEAVY SNOW HAZARD.
THE AFOREMENTIONED TROUGHS ARE FORECAST TO POTENTIALLY UNDERCUT RIDGING
ESTABLISHED OVER THE WESTERN U.S., WITH THE STRONGEST NEGATIVE 500-HPA HEIGHT
DEPARTURES FAVORED ACROSS THE SOUTHWEST, ESPECIALLY EARLY IN THE PERIOD. THIS
SHOULD ALLOW FOR A MORE ACTIVE SOUTHERN STREAM, ALSO AIDED BY RETURN FLOW
AROUND SURFACE HIGH PRESSURE FORECAST ACROSS THE EASTERN CONUS. BEGINNING LATE
IN WEEK-1 AND PERSISTING INTO WEEK-2, ONE OR MORE WAVES OF SURFACE LOW PRESSURE
ARE FORECAST TO DEVELOP ACROSS THE SOUTH-CENTRAL CONUS AND TRACK NORTHEASTWARD.
BOTH THE GEFS AND ECMWF PETS DEPICT PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY HAVING AT LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION
TOTALS EXCEEDING THE 85TH PERCENTILE AND 1-INCH THROUGH THE MIDDLE OF THE
PERIOD. THE ECMWF PET IS MORE EXPANSIVE WITH THE AREA OF ELEVATED
PROBABILITIES, EXTENDING IT FURTHER NORTH INTO THE MIDDLE MISSISSIPPI VALLEY,
AND EAST TOWARD THE SOUTHERN MID-ATLANTIC AND SOUTHEAST. THE SURFACE HIGH
PRESSURE ESTABLISHED OVER THE EAST FAVORS ANY SURFACE LOWS THAT DO DEVELOP
BEING WEAK WITH MORE SUPPRESSED TRACKS. AS A COMPROMISE BETWEEN THE GEFS AND
ECMWF PETS, AND GIVEN THE INCREASED SIGNALS IN PLACE FOR SURFACE LOW
DEVELOPMENT, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR PARTS OF THE
SOUTHERN PLAINS, MIDDLE AND LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND
SOUTHEAST, NOV 11-15. ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON OCTOBER
31, TWO-THIRDS OF LOUISIANA IS DESIGNATED WITH EXCEPTIONAL (D4) DROUGHT AND
EXTREME (D3) DROUGHT COVERS MUCH OF THE TENNESSEE VALLEY. IF THE SOUTHERN
STREAM BECOMES MORE ACTIVE WITH ENHANCED RAINFALL, THEN THIS COULD END THE
WORSENING OF THE DROUGHT DURING MID-NOVEMBER AND EVENTUALLY LEAD TO DROUGHT
RELIEF.
BASED ON CONTINUITY FROM PREVIOUS OUTLOOKS AND SUPPORT FROM THE ECMWF AND GEFS
PETS DEPICTING AT LEAST A 20 PERCENT CHANCE MINIMUM TEMPERATURES FALL BELOW THE
15TH CLIMATOLOGICAL PERCENTILE AND 20 DEG F, A SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES IS POSTED FOR PARTS OF THE NORTHEAST FROM NOV 11-13. THE GEFS
FAVORS THE COLDEST TEMPERATURES ON NOV 11-12 WHILE THE ECMWF DELAYS THE COLDEST
TEMPERATURES UNTIL NOV 12-13. THEREFORE, BOTH PERIODS ARE INCLUDED IN THE
SLIGHT RISK. IT SHOULD BE NOTED THAT THE GROWING SEASON HAS ENDED AND THIS
ANOMALOUS COLD MAY NOT BE TOO HAZARDOUS. LATER IN WEEK-2, AS PACIFIC FLOW
INCREASES THROUGHOUT THE CONUS, TEMPERATURES ARE LIKELY TO MODERATE FOR THE
NORTHEAST.
MID-LEVEL TROUGHING FORECAST OVER THE NORTHEAST PACIFIC FAVORS ABOVE-NORMAL
PRECIPITATION ACROSS SOUTHEASTERN ALASKA. THE MOST LIKELY TIME FOR HEAVY
PRECIPITATION AND HIGH WINDS WOULD BE EARLY IN WEEK-2 WITH MANY 0Z ECMWF
ENSEMBLE MEMBERS FEATURING A LOW PRESSURE SYSTEM (< 978-HPA) OVER THE GULF OF
ALASKA. SINCE THE FORECAST PRECIPITATION AMOUNTS/WIND SPEEDS ARE ONLY MARGINAL,
NO RELATED HAZARD IS POSTED.
FORECASTER: THOMAS COLLOW
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