639
FXUS21 KWNC 021758
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT NOVEMBER 02 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 LOW
PRESSURE OFFSHORE OF THE WEST COAST. PERIODS OF ENHANCED ONSHORE FLOW,
ASSOCIATED WITH THIS MID-LEVEL LOW PRESSURE, 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 THE SOUTHERN GREAT PLAINS, LOWER MISSISSIPPI
VALLEY, AND SOUTHEAST.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND PARTS OF
NORTHERN CALIFORNIA, FRI-THU, NOV 10-16.
SLIGHT RISK OF HIGH WINDS OVER COASTAL PARTS OF THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA, FRI-THU, NOV 10-16.
SLIGHT RISK OF HEAVY PRECIPITATION FOR CENTRAL TO EASTERN TEXAS, THE LOWER
MISSISSIPPI VALLEY, AND TENNESSEE VALLEY, FRI-THU, NOV 10-16.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHEAST,
FRI-SUN, NOV 10-12.
DETAILED SUMMARY
FOR SUNDAY NOVEMBER 05 - THURSDAY NOVEMBER 09:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY NOVEMBER 10 - THURSDAY NOVEMBER 16: EARLY TO MID-NOVEMBER IS LIKELY
TO BE WETTER-THAN-NORMAL ALONG THE WEST COAST AS AN AMPLIFIED 500-HPA TROUGH
PERSISTS OVER THE NORTHEASTERN PACIFIC. THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOLS (PETS) DEPICT AT LEAST A 20 PERCENT CHANCE OF 3-DAY
PRECIPITATION AMOUNTS TO EXCEED THE 85TH PERCENTILE FROM NOVEMBER 10 TO 14, BUT
THE UNCALIBRATED ECMWF MODEL HAS NEAR OR MORE THAN A 20 PERCENT CHANCE THAT
3-DAY TOTALS EXCEED 2 INCHES THROUGH THE END OF WEEK-2. ALSO, THE GEFS ENSEMBLE
DEPICTS A 40 TO 60 PERCENT CHANCE OF INTEGRATED VAPOR TRANSPORT (IVT) EXCEEDING
250 KG/M/S FOR THE COASTAL PACIFIC NORTHWEST THROUGH THE ENTIRETY OF WEEK-2.
BASED ON THE PREDICTED LONGWAVE PATTERN AND CONSENSUS OF PRECIPITATION TOOLS, A
SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR PARTS OF THE PACIFIC NORTHWEST
AND NORTHERN CALIFORNIA FROM NOVEMBER 10 TO 16. CONSISTENT WITH THE AMPLIFIED
TROUGH AND ENHANCED ONSHORE FLOW, A SLIGHT RISK OF HIGH WINDS IS ALSO POSTED
FOR COASTAL AREAS THROUGH THE END OF WEEK-2. 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.
THE RISK OF SANTA ANA WINDS ACROSS SOUTHERN CALIFORNIA IS EXPECTED TO PEAK
PRIOR TO WEEK-2 AND THE ENSEMBLE MEANS DEPICT SURFACE HIGH PRESSURE SHIFTING
EAST OF THE ROCKIES BY DAY 8 (NOV 10) AND ONSHORE FLOW BECOMING MORE PREVALENT.
THEREFORE, THE WIND HAZARD FOR SOUTHERN CALIFORNIA IS DISCONTINUED TODAY.
BY MID-NOVEMBER, THE SOUTHERN STREAM IS FORECAST TO BECOME MORE ACTIVE AS
SHORTWAVE TROUGHS EMERGE FROM THE LONGWAVE TROUGH NEAR THE WEST COAST. AS EARLY
AS DAY 7 (NOV 9), A LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP ACROSS THE
SOUTH-CENTRAL CONUS. THE LONGWAVE PATTERN WOULD SUPPORT MULTIPLE LOW PRESSURE
SYSTEMS WITH ENHANCED PRECIPITATION ACROSS THIS REGION FROM LATE WEEK-1 THROUGH
WEEK-2. DUE TO UNCERTAINTY ON THE TIMING OF INDIVIDUAL SHORTWAVE TROUGHS AND
ASSOCIATED LOW PRESSURE DEVELOPMENT, A SLIGHT RISK OF HEAVY PRECIPITATION IS
POSTED FOR EASTERN TEXAS, THE LOWER MISSISSIPPI VALLEY, AND TENNESSEE VALLEY
FROM NOVEMBER 10 TO 16. THE SLIGHT RISK COVERAGE GENERALLY FOLLOWED THE
PREFERRED UNCALIBRATED ECMWF MODEL GUIDANCE BUT IT ALSO HAS SUPPORT FROM THE
GEFS AND ECMWF PETS. 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 NOVEMBER 10 TO 12. 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 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
HAZARD IS POSTED TODAY.
FORECASTER: BRAD PUGH
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