365
FXUS21 KWNC 021852
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 02 2023
SYNOPSIS: A TRANSIENT PATTERN IS FORECAST DURING WEEK-2 WITH MID-LEVEL LOW
PRESSURE FORECAST TO MOVE OFF THE EASTERN SEABOARD EARLY IN THE PERIOD, AND
MID-LEVEL HIGH PRESSURE BUILDING UPSTREAM OVER THE CENTRAL CONTIGUOUS U.S.
(CONUS). SURFACE HIGH PRESSURE INITIALLY OVER THE EAST FAVORS IDEAL RADIATIONAL
COOLING CONDITIONS, WITH SOME INTERIOR AREAS POSSIBLY HAVING OVERNIGHT
TEMPERATURES COLD ENOUGH TO SUPPORT FROST. ANOTHER AREA OF MID-LEVEL LOW
PRESSURE IS FORECAST TO SHIFT FROM THE GULF OF ALASKA TO THE WEST COAST OF THE
CONUS LEADING TO ENHANCED ONSHORE FLOW AND INCREASED CHANCES FOR ROUNDS OF
HEAVY PRECIPITATION AND HIGH WINDS ACROSS THE PACIFIC NORTHWEST. RAPID ONSET
DROUGHT (ROD) RISK REMAINS ELEVATED ACROSS PARTS OF THE SOUTHEAST QUADRANT OF
THE CONUS DUE TO PROLONGED DRY CONDITIONS AND LITTLE RAINFALL FORECAST IN
WEEK-1, ALTHOUGH THERE ARE SOME INDICATIONS OF INCREASING CHANCES FOR
PRECIPITATION BY THE MIDDLE OF WEEK-2.
HAZARDS
SLIGHT RISK OF EPISODES OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, TUE-THU, OCT 10-12.
SLIGHT RISK OF EPISODES OF HIGH WINDS ACROSS COASTAL PORTIONS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA, TUE-THU, OCT 10-12.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE OHIO AND
TENNESSEE VALLEYS AND APPALACHIANS, TUE-WED, OCT 10-11.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF WESTERN
MAINLAND ALASKA AND THE ALASKA PENINSULA, TUE-SAT, OCT 10-14.
RAPID ONSET DROUGHT (ROD) RISK OVER PARTS OF THE LOWER MISSISSIPPI AND
TENNESSEE VALLEYS, SOUTHEAST AND SOUTHERN APPALACHIANS.
DETAILED SUMMARY
FOR THURSDAY OCTOBER 05 - MONDAY OCTOBER 09:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY OCTOBER 10 - MONDAY OCTOBER 16: MID-LEVEL TROUGHING AND ASSOCIATED
SURFACE HIGH PRESSURE IS FORECAST ACROSS THE EASTERN CONUS BEGINNING LATE IN
WEEK-1 AND INTO EARLY WEEK-2. THIS PATTERN SUPPORTS INCREASED CHANCES FOR BELOW
NORMAL TEMPERATURES, ALTHOUGH IT IS UNCERTAIN WHETHER OR NOT TEMPERATURES WILL
BE COLD ENOUGH TO SUPPORT FROST. THE ECMWF PROBABILISTIC EXTREMES TOOL (PET)
DEPICTS AN EXPANSIVE AREA OF THE EASTERN CONUS WITH AT LEAST A 20 PERCENT
CHANCE OF MINIMUM TEMPERATURES FALLING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE
AND 40 DEG F ON DAYS 8 THROUGH 10 (OCT 10-12). HOWEVER, THE GEFS PET LIMITS
THESE ELEVATED PROBABILITIES TO ONLY PARTS OF THE OHIO AND TENNESSEE VALLEYS
AND APPALACHIANS ON DAY-8 (OCT 10). UNCALIBRATED MINIMUM TEMPERATURES IN THE
GEFS AND ECMWF ENSEMBLES ARE GENERALLY IN THE LOW 40S DEG F ACROSS MUCH OF THE
INTERIOR EASTERN CONUS AT THE BEGINNING OF THE PERIOD. THERE IS AN UPWARD TREND
IN FORECAST MID-LEVEL HEIGHTS AND TEMPERATURES BY THE MIDDLE OF THE PERIOD AS
TROUGHING MOVES OFF THE EAST COAST, ALLOWING RIDGING TO BUILD IN ITS WAKE
ACROSS THE CENTRAL CONUS. GIVEN THE ENHANCED PROBABILITIES IN THE PETS, A
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS HIGHLIGHTED ACROSS PARTS OF
THE OHIO AND TENNESSEE VALLEYS AND APPALACHIANS ON DAYS 8 AND 9 (OCT 10-11)
WHERE RURAL AREAS HAVE THE BEST CHANCES OF MINIMUM TEMPERATURES DIPPING INTO
THE 30S DEG F DUE TO IDEAL CONDITIONS FOR RADIATIONAL COOLING UNDERNEATH
SURFACE HIGH PRESSURE, WHICH MAY LEAD TO AREAS OF FROST AND SUBSEQUENT IMPACTS
TO VEGETATION.
ANOTHER MID-LEVEL TROUGH IS FORECAST TO SHIFT FROM THE GULF OF ALASKA TO THE
WEST COAST OF THE CONUS TOWARD THE END OF WEEK-1, WHICH FAVORS INCREASING
ONSHORE FLOW ACROSS THE PACIFIC NORTHWEST PERSISTING INTO WEEK-2. THE GEFS
INTEGRATED VAPOR TRANSPORT (IVT) TOOL DEPICTS HIGH PROBABILITIES OF IVT
EXCEEDING 250 KG/(MS) LATE IN WEEK-1 INTO THE BEGINNING OF WEEK-2 SIGNIFYING A
POTENTIAL ATMOSPHERIC RIVER EVENT. THE ECMWF PET IS ALSO VERY ROBUST WITH THIS
ANOMALOUS WET SIGNAL, INDICATING SOME AREAS WITH AT LEAST A 60 PERCENT CHANCE
OF 3-DAY PRECIPITATION EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE. HOWEVER,
THE GEFS PET ONLY DEPICTS PROBABILITIES IN THE 20-30 PERCENT RANGE.
ADDITIONALLY, ACTUAL PRECIPITATION TOTALS ARE GENERALLY BETWEEN 1-2 INCHES
SPREAD OUT OVER THE 3-DAY PERIOD IN BOTH THE GEFS AND ECMWF PETS, AS WELL AS
THE UNCALIBRATED GUIDANCE. THEREFORE, ONLY A SLIGHT RISK FOR EPISODES OF HEAVY
PRECIPITATION IS POSTED ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA FOR DAYS 8 THROUGH 10 (OCT 10-12). AN ACCOMPANYING SLIGHT RISK OF
EPISODES OF HIGH WINDS IS ALSO POSTED ALONG COASTAL AREAS OF THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA DUE TO THE FORECAST INCREASED PRESSURE
GRADIENT.
DRY SOILS AND LITTLE TO NO PRECIPITATION FORECAST DURING WEEK-1 CONTINUE TO
SUPPORT AN ELEVATED RAPID ONSET DROUGHT (ROD) RISK OVER PARTS OF THE LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, SOUTHEAST AND SOUTHERN APPALACHIANS. AN
UPWARD TREND IN TEMPERATURES IS ALSO FORECAST LATER IN WEEK-2 OVER THESE AREAS
AS RIDGING BUILDS WHICH COULD ALSO HELP PROMOTE INCREASED EVAPORATION RATES
DESPITE THE DECREASING SUN ANGLE IN MID-OCTOBER. WHILE DRY CONDITIONS LOOK TO
PERSIST THROUGH ABOUT DAY-10 (OCT 12), PRECIPITATION CHANCES MAY BEGIN TO
INCREASE LATER IN WEEK-2 AS THE SOUTHERN STREAM POTENTIALLY BECOMES MORE
ACTIVE, WHICH MAY PROVIDE SOME RELIEF.
PERSISTENT MID-LEVEL TROUGHING FORECAST ACROSS ALASKA FAVORS BELOW-NORMAL
TEMPERATURES ACROSS MUCH OF THE STATE. THE ECMWF AND GEFS PETS INDICATE AT
LEAST A 20 PERCENT CHANCE OF MINIMUM TEMPERATURES FALLING BELOW THE 15TH
CLIMATOLOGICAL PERCENTILE AND 20 DEG F ACROSS MUCH OF WESTERN MAINLAND ALASKA
AND THE ALASKA PENINSULA, SUPPORTING A SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES, OCT 10-14. THIS COULD LEAD TO INCREASING FREEZE-UP OF RIVERS AND
LAKES.
FORECASTER: THOMAS COLLOW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page