965
FXUS21 KWNC 101906
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 10 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE AND SURFACE HIGH PRESSURE ARE FORECAST TO
CONTINUE TO BRING ELEVATED CHANCES FOR MUCH BELOW NORMAL TEMPERATURES INTO
PORTIONS OF THE EASTERN CONTIGUOUS U.S. (CONUS) EARLY IN WEEK-2. MEANWHILE,
ABOVE-NORMAL PRECIPITATION CHANCES REMAIN FAVORED ACROSS PORTIONS OF SOUTHERN
AND SOUTHEAST ALASKA AS WELL AS THE PACIFIC NORTHWEST, BUT ARE NOT FORECAST TO
REACH HAZARDOUS THRESHOLDS. SOME GUIDANCE TOOLS INDICATE THE INCREASED
POTENTIAL FOR HEAVY PRECIPITATION ACROSS THE CENTRAL AND SOUTHERN GREAT PLAINS
EARLY IN WEEK-2, BUT THERE IS NOT ENOUGH CONSISTENCY WITH THIS FEATURE TO POST
ANY ASSOCIATED HAZARDS AT THIS TIME.
HAZARDS
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PARTS OF THE MIDDLE
MISSISSIPPI, LOWER OHIO, AND TENNESSEE VALLEYS AND ACROSS THE INTERIOR
SOUTHEAST, WED-THU, OCT 18-19.
DETAILED SUMMARY
FOR FRIDAY OCTOBER 13 - TUESDAY OCTOBER 17:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY OCTOBER 18 - TUESDAY OCTOBER 24: AN AMPLIFIED 500-HPA HEIGHT
PATTERN IS FORECAST ACROSS NORTH AMERICA AND THE SURROUNDING AREAS AT THE START
OF WEEK-2, WITH ANOMALIES GENERALLY DECLINING AS THE WEEK PROGRESSES. 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 THIS REGION. SOME OF THE MOST
ANOMALOUS TEMPERATURES COULD AFFECT SOUTHERN FLORIDA, WHERE THE ECWMF
PROBABILISTIC EXTREMES TOOL (PET) TOOL SHOWS ODDS EXCEEDING 40 PERCENT OF
TEMPERATURES DROPPING INTO THE COLDEST 5 PERCENT OF THE CLIMATOLOGICAL ENVELOPE
ON DAY 8 (OCT 18), WITH THE GEFS PET INDICATING AT LEAST A 20 PERCENT CHANCE OF
TEMPERATURES FALLING IN THE LOWEST 5 PERCENT CLIMATOLOGICALLY. HOWEVER,
TEMPERATURES ARE NOT DEEMED HAZARDOUS IN THIS REGION SINCE TEMPERATURES ARE
EXPECTED TO REMAIN ABOUT 40 DEG F. FARTHER NORTH, THERE ARE ELEVATED CHANCES OF
TEMPERATURES DROPPING BELOW THE 15TH PERCENTILE ACCORDING TO THE ECMWF ENSEMBLE
AND GEFS PETS, ALONG WITH TEMPERATURES DROPPING BELOW 40 DEG F FROM THE OHIO
VALLEY SOUTHWARD THROUGH THE INTERIOR SOUTHEAST. VEGETATION IN THIS REGION
COULD BE SUSCEPTIBLE TO FORECAST TEMPERATURES. CONDITIONS WILL BE MODERATING AS
WEEK-2 PROGRESSES, AND THE COLD WEATHER THREAT SHOULD BE OVER BY DAY 10 (OCT
20).
THE MAIN INCONSISTENCY IN TODAY’S GUIDANCE CONCERNS THE POTENTIAL FOR A
MID-LEVEL SHORT WAVE EJECTING OUT OF THE CENTRAL NORTH PACIFIC TROUGH WHICH MAY
TRAVERSE THE CONUS OVER THE FIRST HALF OF WEEK-2. THE EUROPEAN ENSEMBLE MEANS
AND THEIR DERIVEDPETS SHOW 40 TO NEAR 60 PERCENT CHANCES FOR PRECIPITATION
EXCEEDING THE 85TH PERCENTILE DAYS 8-10 (OCT 18-20) THROUGHOUT THE CENTRAL AND
SOUTHERN GREAT PLAINS, WHILE OTHER GUIDANCE IS LESS ROBUST WITH THE MID-LEVEL
FEATURE AND, THEREFORE, ALSO WITH THEIR PRECIPITATION FORECASTS. WHILE HEAVY
PRECIPITATION IS POSSIBLE EARLY WEEK-2 FOR THESE REGIONS, THE UNCERTAINTY OF
THE SITUATION PRECLUDES ANY HAZARDS BEING POSTED AT THIS TIME.
A MID-LEVEL TROUGH OVER THE NORTHEAST PACIFIC IS FAVORED TO PROMOTE
ABOVE-NORMAL PRECIPITATION IN THE PACIFIC NORTHWEST AND SOUTHEAST ALASKA.
TODAY’S GUIDANCE SHIFTED THE HEAVIEST PRECIPITATION NORTHWARD COMPARED TO
YESTERDAY, INTO SOUTH-CENTRAL AND SOUTHEAST ALASKA. THEES AREAS ARE PREDICTED
TO BE UNDER MID-LEVEL CYCLONIC CURVATURE, WITH MOIST, MILD SURFACE FLOW FROM
THE NORTH PACIFIC OCEAN AT THE SURFACE. THE GEFS AND ECMWF PETS INDICATE A 20%
OR GREATER CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE DURING
THE FIRST PART OF WEEK-2 BEFORE THE MID-LEVEL TROUGH STARTS TO WEAKEN AND GETS
SHEARED OUT. THREE-DAY PRECIPITATION AMOUNTS ARE FORECAST TO EXCEED 2 INCHES IN
SOUTHEAST ALASKA AND SOUTHERN ALASKA. DUE TO THIS BEING THE WETTEST TIME OF THE
YEAR CLIMATOLOGICALLY FOR THESE REGIONS, WITH NORMAL OCTOBER PRECIPITATION
APPROACHING 2 FEET IN PARTS OF SOUTHEAST ALASKA,, PRECIPITATION AMOUNTS ARE
EXPECTED TO REMAIN BELOW THREAT LEVELS. HOWEVER THIS COULD CHANGE IF THE MODEL
TREND TOWARD INCREASING PRECIPITATION CONTINUES.
FORECASTER: RICH TINKER
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