690
FXUS21 KWNC 111824
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 11 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE AND SURFACE HIGH PRESSURE ARE FORECAST TO
CONTINUE TO BRING ELEVATED CHANCES FOR MUCH BELOW NORMAL TEMPERATURES TO
PORTIONS OF THE EASTERN CONTIGUOUS U.S. (CONUS) EARLY IN WEEK-2. MEANWHILE,
SURFACE LOW PRESSURE OVER THE GULF OF ALASKA SUPPORTS INCREASED CHANCES FOR
ENHANCED PRECIPITATION AND HIGH WINDS ACROSS SOUTHERN AND SOUTHEAST ALASKA AS
WELL AS THE PACIFIC NORTHWEST AT THE BEGINNING OF THE PERIOD. PASSAGE OF A
FRONTAL BOUNDARY MAY BRING HEAVY RAIN TO PARTS OF THE SOUTHERN PLAINS AND THE
LOWER MISSISSIPPI VALLEY EARLY IN WEEK-2, ALTHOUGH THERE ARE SIGNIFICANT MODEL
DIFFERENCES REGARDING THIS POTENTIAL.
HAZARDS
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE OHIO AND
TENNESSEE VALLEYS, APPALACHIANS, MID-ATLANTIC, AND SOUTHEAST, THU-FRI, OCT
19-20.
SLIGHT RISK OF HIGH WINDS ACROSS COASTAL PORTIONS OF THE KENAI PENINSULA AND
SOUTHEASTERN ALASKA, THU-SAT, OCT 19-21.
DETAILED SUMMARY
FOR SATURDAY OCTOBER 14 - WEDNESDAY OCTOBER 18:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY OCTOBER 19 - WEDNESDAY OCTOBER 25: A FAIRLY AMPLIFIED 500-HPA
HEIGHT PATTERN IS FORECAST ACROSS NORTH AMERICA FOR WEEK-2, WITH ANOMALOUS
POSITIVE (NEGATIVE) MID-LEVEL HEIGHTS ACROSS THE WESTERN (EASTERN) CONUS. FOR
THE MEAN WEEK-2 PATTERN, THERE IS GOOD AGREEMENT AMONG MULTIPLE MODELS
REGARDING A MID-LEVEL TROUGH CENTERED OVER THE CENTRAL NORTH PACIFIC, WITH
ABOVE-NORMAL 500-HPA HEIGHTS FARTHER NORTH AND EAST ACROSS ALASKA WITH
DOWNSTREAM RIDGING OVER WESTERN NORTH AMERICA. FARTHER EAST, A MID-LEVEL TROUGH
OVER OR NEAR THE EASTERN CONUS WEAKENS AND DRIFTS EASTWARD OFF THE EAST COAST.
A MID-LEVEL TROUGH OVER THE EASTERN CONUS AT THE BEGINNING OF THE PERIOD FAVORS
UNSEASONABLY COLD AIR ACROSS PORTIONS OF THE REGION. THE ECWMF PROBABILISTIC
EXTREMES TOOL (PET) TOOL SHOWS THE GREATEST ODDS FOR ANOMALOUS COLD ACROSS
FLORIDA AND SOUTHERN GEORGIA, INDICATING AT LEAST A 20% CHANCE OF TEMPERATURES
DROPPING INTO THE COLDEST 5TH PERCENTILE CLIMATOLOGICALLY ON DAY 8 (OCT 18),
WITH THE GEFS PET INDICATING LESS THAN 10 PERCENT CHANCE OF REACHING THESE
THRESHOLDS. A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS HIGHLIGHTED
ACROSS PARTS OF THE OHIO AND TENNESSEE VALLEYS, APPALACHIANS, MID-ATLANTIC, AND
SOUTHEAST, OCT 19-20, WHERE THE GEFS AND ECMWF PETS DEPICT AT LEAST A 20%
CHANCE OF FALLING BELOW THE LOWEST 15TH PERCENTILE AND 40 DEG F AND WHERE THERE
IS SUSCEPTIBLE VEGETATION ACCORDING TO THE MIDWESTERN REGIONAL CLIMATE CENTER
(MRCC) OR WHERE THIS WOULD BE THE FIRST TIME TEMPERATURES COULD APPROACH NEAR
FREEZING FOR THE SEASON.
THERE CONTINUES TO BE SIGNIFICANT MODEL DIFFERENCES REGARDING THE POTENTIAL FOR
HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTH-CENTRAL/SOUTHEASTERN CONUS AT
THE BEGINNING OF THE PERIOD ASSOCIATED WITH THE PASSAGE OF A FRONT. THE ECMWF
AND CANADIAN PETS SHOW AT LEAST A 20% OF 3-DAY RAINFALL TOTALS EXCEEDING THE
85TH PERCENTILE AND ONE INCH ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY, OCT 19-21. THE GEFS COUNTERPART, HOWEVER, DOES NOT REACH
THESE THRESHOLDS. DUE TO THIS HIGH UNCERTAINTY A RELATED HAZARD IS NOT POSTED.
THE REMNANTS OF WHAT IS CURRENTLY SUPER TYPHOON BOLAVEN (LOCATED EAST OF THE
PHILIPPINES AS OF THIS MORNING), MAY BRING ENHANCED PRECIPITATION AND HIGH
WINDS TO PORTIONS OF THE SOUTHERN AND SOUTHEASTERN MAINLAND OF ALASKA BY THE
ONSET OF WEEK-2. THE GEFS, ECMWF, AND CANADIAN PETS SHOW LOCALIZED AREAS ACROSS
THE KENAI PENINSULA AND SOUTHEASTERN ALASKA REACHING AT LEAST A 20% CHANCE OF
3-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE. HOWEVER, THE 3-DAY
TOTALS ARE ANTICIPATED TO REMAIN BELOW 3 INCHES, PRECLUDING A RELATED
PRECIPITATION HAZARD FROM BEING DESIGNATED AT THIS TIME. THERE IS HOWEVER A
SLIGHT RISK OF HIGH WINDS THAT IS POSTED ACROSS COASTAL PORTIONS OF THE
SOUTHERN AND SOUTHEASTERN MAINLAND, OCT 19-21. THE PETS ARE IN GOOD AGREEMENT
INDICATING AT LEAST A 20% CHANCE OF WIND SPEEDS EXCEEDING THE 85TH PERCENTILE
AND 40 MPH IN THESE AREAS. ADDITIONALLY, THERE IS GOOD AGREEMENT AMONG
DETERMINISTIC MODELS INDICATING THIS STRONG SURFACE LOW BY WEEK-2.
FORECASTER: MELISSA OU
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