337
FXUS21 KWNC 261940
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 26 2024
SYNOPSIS: MODEL ENSEMBLES DEPICT HIGH PRESSURE BOTH AT THE SURFACE AND
MID-LEVELS ACROSS THE WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS) DURING
WEEK-2, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF THE
NORTHWESTERN CONUS FOR THE FIRST HALF OF THE FORECAST PERIOD. A STALLED FRONTAL
BOUNDARY OVER THE SOUTHEASTERN CONUS IS FAVORED TO COMBINE WITH TROPICAL
MOISTURE, POTENTIALLY BRINGING HEAVY PRECIPITATION TO PORTIONS OF THE GULF
COAST AND MID-ATLANTIC. LOW PRESSURE AT THE SURFACE AND MID-LEVELS OVER THE
GULF OF ALASKA FAVORS STORMY CONDITIONS AND POSSIBLY HAZARDOUS PRECIPITATION TO
PORTIONS OF SOUTHEASTERN ALASKA. PROLONGED RAINFALL DEFICITS COMBINED WITH
CONTINUED ABOVE-NORMAL TEMPERATURES RESULTS IN THE POTENTIAL FOR RAPID ONSET
DROUGHT FOR PARTS OF THE SOUTHERN PLAINS AND THE OHIO, TENNESSEE, AND
MISSISSIPPI VALLEYS.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE NORTHERN GREAT BASIN,
NORTHERN ROCKIES, AND NORTHERN PLAINS, TUE-FRI, SEP 3-6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GULF COAST, SOUTHEAST
U.S., AND MID-ATLANTIC, TUE-SAT, SEP 3-7.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE ALASKA PANHANDLE, TUE-THU, SEP 3-5.
RISK FOR RAPID ONSET DROUGHT FOR PORTIONS OF THE SOUTHERN PLAINS, AND THE OHIO,
TENNESSEE, AND LOWER AND MIDDLE MISSISSIPPI VALLEYS.
DETAILED SUMMARY
FOR THURSDAY AUGUST 29 - MONDAY SEPTEMBER 02:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY SEPTEMBER 03 - MONDAY SEPTEMBER 09: TODAY’S MODEL SOLUTIONS FOR 500
HPA HEIGHTS AND ANOMALIES DEPICT AN AMPLIFIED RIDGE OVER THE NORTHWESTERN CONUS
AT THE OUTSET OF WEEK-2, AND TROUGHS OVER THE GULF OF ALASKA AND THE GREAT
LAKES. WHILE THESE FEATURES SHIFT AROUND SOMEWHAT DURING THE FORECAST PERIOD
THEY REMAIN FAIRLY CONSISTENT THROUGHOUT. RIDGING ALOFT AND HIGH PRESSURE AT
THE SURFACE LEADS TO THE POTENTIAL FOR EXCESSIVE HEAT ALONG THE NORTHERN TIER.
THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) BOTH INDICATE AT LEAST A
20% PROBABILITY OF MAXIMUM TEMPERATURES EXCEEDING THE 90TH PERCENTILE AND AT
LEAST 90F FOR PORTIONS OF THE NORTHWESTERN CONUS THROUGH DAY-11 (SEP 6). THERE
ARE INDICATIONS THAT THE RISK FOR EXCESSIVE HEAT COULD EXTEND BEYOND THIS BUT
GIVEN CURRENT MODEL SOLUTIONS A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED FOR
PORTIONS OF THE NORTHERN GREAT BASIN, NORTHERN ROCKIES, AND NORTHERN PLAINS FOR
SEP 3-6.
AN EXTENSION OF THE BERMUDA HIGH OVER THE SOUTHEAST U.S. IS DEPICTED IN TODAY’S
MODEL SOLUTIONS WHICH WOULD INCREASE RETURN FLOW OFF THE GULF OF MEXICO. A
STALLED FRONTAL SYSTEM IS DEPICTED OVER THE SOUTHEASTERN CONUS AT THE OUTSET OF
WEEK-2, WHICH COMBINED WITH INCREASED TROPICAL MOISTURE LEADS TO THE POTENTIAL
FOR HEAVY PRECIPITATION. THE PETS INDICATE A 20% CHANCE OF 3-DAY TOTAL
PRECIPITATION EXCEEDING THE 85TH PERCENTILE AND AT LEAST 1 INCH FOR PORTIONS OF
THE GULF COAST AND EXTENDING NORTHWARD ALONG THE EAST COAST FOR MUCH OF THE
FORECAST PERIOD DUE TO THIS INCREASED RETURN FLOW POTENTIAL. THE SIGNAL WEAKENS
A LITTLE AT THE END OF WEEK-2, THEREFORE A SLIGHT RISK FOR HEAVY PRECIPITATION
IS POSTED FOR PORTIONS OF THE GULF COAST, SOUTHEAST U.S., AND MID-ATLANTIC FOR
SEP 3-7.
THE PETS ALSO INDICATE INCREASED CHANCES FOR HEAVY PRECIPITATION FOR
SOUTHEASTERN ALASKA DUE TO AN AMPLIFIED TROUGH OVER THE GULF OF ALASKA,
POTENTIALLY ENHANCED BY TROPICAL MOISTURE INFLUXES FROM EXTRATROPICAL SYSTEMS
EMERGING FROM THE WESTERN PACIFIC. THIS POTENTIAL IS GREATEST EARLY IN WEEK-2,
WITH THE ECMWF PET INDICATING WIDESPREAD PROBABILITIES OF AT LEAST 20% OF 3-DAY
PRECIPITATION EXCEEDING 2 INCHES, WITH 3 INCHES POSSIBLE IN SOME LOCATIONS.
THUS A SLIGHT RISK FOR HEAVY PRECIPITATION IS POSTED FOR THE ALASKA PANHANDLE
FOR SEP 3-5. THE SOIL IN THIS REGION IS ALREADY SATURATED DUE TO HEAVY
ANTECEDENT RAINFALL AND LANDSLIDES HAVE BEEN AN ONGOING CONCERN, A PROBLEM
WHICH MAY BE EXACERBATED BY THIS POTENTIALLY HAZARDOUS PRECIPITATION.
NEAR- TO BELOW-NORMAL RAINFALL ANTICIPATED OVER MUCH OF THE NORTH-CENTRAL AND
EAST-CENTRAL CONUS DURING WEEK-2 COMBINED WITH AN INCREASED LIKELIHOOD OF
EXCESSIVE HEAT DURING WEEK-1 AND BELOW-NORMAL 30-DAY ACCUMULATED PRECIPITATION,
RESULTS IN AN ELEVATED RISK OF RAPID ONSET DROUGHT (ROD) ACROSS PORTIONS OF THE
SOUTHERN PLAINS AND PARTS OF THE MISSISSIPPI, TENNESSEE AND OHIO VALLEYS. THIS
IS FURTHER SUPPORTED BY DECLINING OBSERVED SOIL MOISTURE VALUES AND DRY
CONDITIONS FAVORED OVER THE NEXT TWO WEEKS. TODAY THE TEXAS PANHANDLE AND WEST
TEXAS HAVE BEEN REMOVED FROM THE AREA HIGHLIGHTED FOR ROD RISK DUE TO
WIDESPREAD ANTICIPATED RAINFALL AMOUNTING TO AT LEAST 1 INCH DURING WEEK-1 OVER
THIS REGION.
FORECASTER: DANNY BARANDIARAN
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