752
FXUS21 KWNC 191811
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 19 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE OFF THE WEST COAST IS FAVORED TO BRING PERIODS
OF POTENTIALLY HIGH WIND AND HEAVY RAIN TO COASTAL PORTIONS OF THE NORTHWEST
CONTIGUOUS U.S. (CONUS). A SURFACE LOW PRESSURE IS FORECAST TO FORM OFF THE
COAST OF THE SOUTHEAST U.S. LATE IN WEEK-1, BRINGING WITH IT THE POTENTIAL FOR
HEAVY PRECIPITATION FOR PORTIONS OF THE EAST COAST. CONTINUED DRY CONDITIONS
AND UNSEASONABLY WARM TEMPERATURES RESULT IN A RISK FOR RAPID ONSET DROUGHT
(ROD) ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.
HAZARDS
SLIGHT RISK FOR HEAVY PRECIPITATION FOR WESTERN PORTIONS OF WASHINGTON, OREGON,
AND NORTHERN CALIFORNIA, WED-SAT, SEP 27-30.
SLIGHT RISK FOR HIGH WINDS FOR COASTAL PORTIONS OF WASHINGTON, OREGON, AND
CALIFORNIA NORTH OF POINT CONCEPTION, WED-SAT, SEP 27-30.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST,
MID-ATLANTIC, AND NEW ENGLAND, WED-FRI, SEP 27-29.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF MISSISSIPPI, ALABAMA, AND SOUTHEAST
ARKANSAS.
DETAILED SUMMARY
FOR FRIDAY SEPTEMBER 22 - TUESDAY SEPTEMBER 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY SEPTEMBER 27 - TUESDAY OCTOBER 03: AT THE ONSET OF THE WEEK-2
PERIOD THE CONSENSUS AMONG ENSEMBLE FORECAST MODELS FOR 500-HPA HEIGHT
ANOMALIES DEPICT A DEEP ANOMALOUS TROUGH SITUATED OFF THE COAST OF THE PACIFIC
NORTHWEST. THIS TROUGH LOOKS LIKELY TO WEAKEN BY THE MIDDLE TO END OF THE
FORECAST PERIOD. HOWEVER, FORECAST GUIDANCE INDICATES THE POTENTIAL FOR A
SERIES OF SHORTWAVE TROUGHS TO COME ASHORE NEAR THE U.S.-CANADA BORDER,
RESULTING IN INCREASED CHANCES FOR HEAVY RAIN AND HIGH WINDS. THE ECMWF, GEFS,
AND CMCE PROBABILISTIC EXTREMES TOOLS (PETS) ALL INDICATE PROBABILITIES OF AT
LEAST 20% FOR THREE-DAY PRECIPITATION TOTALS EXCEEDING THE 85TH PERCENTILE AND
1 INCH FOR WESTERN PORTIONS OF WASHINGTON, OREGON, AND CALIFORNIA NORTH OF THE
BAY AREA, THUS A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR THESE AREAS
FOR SEP 27-30. ADDITIONALLY, THE PETS ALSO INDICATE AT LEAST A 20% CHANCE OF
WIND SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH FOR COASTAL PORTIONS OF
WASHINGTON, OREGON, AND CALIFORNIA AS FAR SOUTH AS POINT CONCEPTION FOR THE
SAME TIME PERIOD, SEP 27-30.
LATE IN WEEK-1 AN AREA OF SURFACE LOW PRESSURE IS FAVORED TO FORM ALONG THE
COAST OF THE CAROLINAS. THE NATIONAL HURRICANE CENTER IS FORECASTING A 30%
CHANCE OF A SUBTROPICAL CYCLONE DEVELOPING IN THIS AREA, BUT REGARDLESS OF
DEVELOPMENT, THE AREA OF LOW-PRESSURE IS LIKELY TO ENHANCE CHANCES OF HEAVY
PRECIPITATION ALONG THE EASTERN SEABOARD. THE ECMWF AND CMCE PETS INDICATE AT
LEAST A 20% CHANCE OF 3 DAY PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND 1
INCH OF PRECIPITATION FOR THE CAROLINAS EXTENDING INTO EVEN PARTS OF NEW
ENGLAND. WHILE THE GEFS PET HEAVY PRECIPITATION TOTALS ARE NOT AS ANOMALOUS IN
PERCENTILE SPACE, IT CONTINUES TO INDICATE A 20% CHANCE OF 3 DAY PRECIPITATION
TOTALS EXCEEDING 0.75 INCHES. HOWEVER, RAW PRECIPITATION GUIDANCE TOOLS ARE A
LITTLE LESS SUPPORTIVE. NEVERTHELESS, WITH FAIRLY BROAD SUPPORT FROM
PROBABILISTIC TOOLS, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR SEP
27-29 FOR PORTIONS OF THE CAROLINAS, MID-ATLANTIC, AND SOUTHERN NEW ENGLAND.
ANOMALOUS POSITIVE 500-HPA ANOMALIES OVER NORTHERN CANADA AND ASSOCIATED RIDGE
AXIS EXTENDING SOUTHWARD WELL INTO THE CONUS FAVOR ABOVE-NORMAL TEMPERATURES
ESPECIALLY FOR THE NORTHERN PLAINS AND THE GULF COAST. CLIMATOLOGICAL VALUES
DURING THIS TIME OF YEAR ARE MUCH LOWER THAN DURING THE HEART OF SUMMER, SO
WHILE TEMPERATURE ANOMALIES QUALIFY AS EXTREME IN PERCENTILE SPACE, THEY ARE
NOT LIKELY TO REACH HAZARDOUS CRITERIA IN ABSOLUTE TERMS SO NO
TEMPERATURE-RELATED HAZARDS ARE POSTED AT THIS TIME.
DROUGHT CONCERNS ARE FORECAST TO CONTINUE FOR PORTIONS OF THE LOWER MISSISSIPPI
VALLEY. ABOVE-NORMAL TEMPERATURES, ANTECEDENT DRYNESS FOR SOUTHERN MISSISSIPPI
AND ALABAMA IN PARTICULAR AND LITTLE PRECIPITATION IN THE FORECAST RESULT IN
THE CONTINUED RISK FOR ROD DEVELOPMENT FOR THIS REGION, SO NO CHANGES ARE MADE
TO THE ROD OUTLOOK TODAY.
FORECASTER: RYAN BOLT
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