986
FXUS21 KWNC 181851
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 18 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 MID-ATLANTIC STATES AND THE TENNESSEE
VALLEY. CONTINUED DRY CONDITIONS AND UNSEASONABLY WARM TEMPERATURES RESULT IN A
RISK FOR RAPID ONSET DROUGHT (ROD).
HAZARDS
SLIGHT RISK FOR HEAVY PRECIPITATION FOR WESTERN PORTIONS OF WASHINGTON, OREGON,
AND CALIFORNIA NORTH OF THE GOLDEN GATE, TUE-SAT, SEP 26-30.
SLIGHT RISK FOR HIGH WINDS FOR COASTAL PORTIONS OF WASHINGTON, OREGON, AND
CALIFORNIA NORTH OF POINT CONCEPTION, TUE-SAT, SEP 26-30.
SLIGHT RISK FOR HEAVY PRECIPITATION FOR PORTIONS OF THE TENNESSEE VALLEY AND
THE MID-ATLANTIC, TUE-FRI, SEP 26-29.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF MISSISSIPPI, ALABAMA, AND SOUTHEAST
ARKANSAS.
DETAILED SUMMARY
FOR THURSDAY SEPTEMBER 21 - MONDAY SEPTEMBER 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY SEPTEMBER 26 - MONDAY OCTOBER 02: 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.
BY THE END OF THE FORECAST PERIOD THE AMPLITUDE OF THIS TROUGH IS SUBSTANTIALLY
DIMINISHED BUT NOT BEFORE USHERING A SERIES OF SHORTWAVE TROUGHS THAT ARE
FAVORED TO COME ASHORE NEAR THE U.S.-CANADA BORDER, RESULTING IN EPISODES OF
STORMY WEATHER. THE ECMWF, GEFS, AND CMCE PROBABILISTIC EXTREMES TOOLS (PET)
ALL INDICATE PROBABILITIES OF AT LEAST 20% FOR THREE-DAY PRECIPITATION TOTALS
TO EXCEED THE 85TH PERCENTILE AND 1 INCH TOTAL FOR WESTERN PORTIONS OF
WASHINGTON, OREGON, AND CALIFORNIA NORTH OF THE BAY AREA, THEREFORE A SLIGHT
RISK FOR HEAVY PRECIPITATION IS POSTED FOR THESE AREAS FOR SEP 26-30.
ADDITIONALLY, THE PETS ALSO INDICATE AT LEAST A 20% CHANCE OF WIND SPEED
EXCEEDING THE 85TH PERCENTILE AND 25MPH FOR COASTAL PORTIONS OF WASHINGTON,
OREGON, AND CALIFORNIA AS FAR SOUTH AS POINT CONCEPTION FOR THE SAME TIME
PERIOD, SEP 26-30.
ANOTHER FEATURE IN ENSEMBLE MODEL SOLUTIONS EARLY IN WEEK-2 IS AN AREA OF
SURFACE LOW PRESSURE NEAR THE COAST OF THE CAROLINAS. THIS FEATURE FAVORS
ENHANCED PRECIPITATION FOR PORTIONS OF THE MID-ATLANTIC STATES AND THE
TENNESSEE VALLEY. THE PETS HIGHLIGHT THESE REGIONS WITH THE POTENTIAL FOR 3-DAY
PRECIPITATION TO EXCEED THE 85TH PERCENTILE AND 1 INCH FOR THE FIRST HALF OF
THE FORECAST PERIOD, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED
FOR SEP 26-29.
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: DANNY BARANDIARAN
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