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FXUS21 KWNC 221825
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 22 2024
SYNOPSIS: MODEL ENSEMBLES DEPICT HIGH PRESSURE BOTH AT THE SURFACE AND
MID-LEVELS ACROSS THE CENTRAL CONTIGUOUS U.S. (CONUS) EARLY IN THE FORECAST
PERIOD, LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT FOR PORTIONS OF THE GREAT
PLAINS AND THE OHIO AND MISSISSIPPI VALLEYS. 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 MISSISSIPPI, TENNESSEE, AND
OHIO VALLEYS, GREAT LAKES, AND SOUTHEAST U.S., FRI, AUG 30.
RISK FOR RAPID ONSET DROUGHT FOR PORTIONS OF THE SOUTHERN PLAINS, AND THE OHIO,
TENNESSEE, AND LOWER AND MIDDLE MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SUNDAY AUGUST 25 - THURSDAY AUGUST 29:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 30 - THURSDAY SEPTEMBER 05: TODAY’S MODEL SOLUTIONS FOR 500
HPA HEIGHTS AND ANOMALIES DEPICT BROAD RIDGING OVER THE CONUS AT THE OUTSET OF
WEEK-2 WITH A RIDGE AXIS ROUGHLY OVER THE GREAT PLAINS. THIS RIDGE WEAKENS
GRADUALLY THROUGHOUT THE FORECAST PERIOD AS A WEAK TROUGH BEGINS TO TAKE SHAPE
OVER THE GREAT LAKES REGION. THE EARLY RIDGING LEADS TO THE POTENTIAL FOR
EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL AND EASTERN CONUS, ALTHOUGH MOST OF
THE RISK IS NOW IN THE WEEK-1 PERIOD. THE GEFS AND ECMWF PROBABILISTIC EXTREMES
TOOLS (PETS) BOTH INDICATE AT LEAST A 20% PROBABILITY OF MAXIMUM TEMPERATURES
EXCEEDING THE 90TH PERCENTILE AND 90F AS FAR NORTH AS CHICAGO, AND POSSIBLY
OVER 100F FOR PORTIONS OF NORTH TEXAS AT THE OUTSET OF WEEK-2. A DEVELOPING
TROUGH OVER THE GREAT LAKES REDUCES POTENTIAL FOR EXCESSIVE HEAT VERY QUICKLY
SO A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED FOR PORTIONS OF THE MISSISSIPPI,
TENNESSEE, AND OHIO VALLEYS, GREAT LAKES, AND SOUTHEAST U.S. FOR AUG 30 ONLY.
HURRICANE GILMA IS AN ACTIVE TROPICAL CYCLONE (TC) LOCATED MORE THAN 2000 MILES
EAST-SOUTHEAST OF HAWAII AND MOVING GENERALLY WEST IN THE CENTRAL PACIFIC.
CURRENTLY, THE NATIONAL HURRICANE CENTER (NHC) FORECASTS GILMA TO CONTINUE TO
TRACK ROUGHLY DUE WEST AS A MAJOR HURRICANE, BUT IS ANTICIPATED TO WEAKEN AS IT
APPROACHES THE HAWAIIAN ISLANDS EARLY IN WEEK-2. THIS TC HAS THE POTENTIAL TO
BRING HEAVY RAIN, STRONG WINDS, AND DANGEROUS SURF. AREAS AFFECTED BY RECENT
WILDFIRES WOULD ALSO BE AT ELEVATED RISK FOR LANDSLIDES AND DEBRIS FLOWS. THERE
IS STILL A GREAT DEAL OF UNCERTAINTY REGARDING THE EVOLUTION OF GILMA BUT THE
SITUATION WILL BE CLOSELY MONITORED IN THE COMING DAYS. FOLLOWING TC GILMA, THE
NHC IS TRACKING ANOTHER DISTURBANCE ACROSS THE EASTERN PACIFIC THAT MAY IMPACT
HAWAII DURING THE WEEK-2 PERIOD. UNCERTAINTY REMAINS HIGH WITH THIS SYSTEM
HOWEVER, INTERESTS IN HAWAII SHOULD CONTINUE TO MONITOR THE NHC AND THE CENTRAL
PACIFIC HURRICANE CENTER (CPHC) FOR DEVELOPMENT OF THIS SYSTEM.
DEVELOPING SURFACE PRESSURE OVER THE TENNESSEE VALLEY IS DEPICTED IN TODAY’S
MODEL SOLUTIONS WHICH WOULD INCREASE RETURN FLOW OFF THE GULF OF MEXICO AND
INTO THE GREAT PLAINS, GENERALLY INCREASING THE POTENTIAL FOR HEAVY
PRECIPITATION. THE PETS INDICATE A 20% CHANCE OF 3-DAY TOTAL PRECIPITATION
EXCEEDING THE 85TH PERCENTILE FOR PORTIONS OF THE GULF COAST AND EXTENDING
NORTHWARD INTO THE SOUTHERN AND CENTRAL PLAINS DUE TO THIS INCREASED RETURN
FLOW POTENTIAL, BUT ABSOLUTE RAINFALL TOTALS ARE NOT EXPECTED TO EXCEED
HAZARDOUS THRESHOLDS SO NO HEAVY PRECIPITATION HAZARD IS POSTED AT THIS TIME.
THE ECMWF PET ALSO INDICATES A SIMILAR POTENTIAL FOR HEAVY PRECIPITATION FOR
THE SOUTHERN COAST OF ALASKA, BUT SIMILAR TO THE GULF COAST, PRECIPITATION
TOTALS ARE NOT EXPECTED TO EXCEED HAZARDOUS THRESHOLDS SO NO ASSOCIATED HAZARD
IS DESIGNATED.
THE ECMWF PET FOR MAXIMUM WIND SPEED INDICATES AT LEAST A 20% PROBABILITY FOR
WIND SPEEDS TO EXCEED THE 85TH PERCENTILE OVER THE FIRST HALF OF WEEK-2,
HOWEVER ABSOLUTE MAXIMUM VALUES FROM BOTH ECMWF AND GEFS FOR THE RELEVANT TIME
PERIOD DO NOT EXCEED HAZARDOUS THRESHOLDS SO NO ASSOCIATED HAZARD IS POSTED AT
THIS TIME.
NEAR- TO BELOW-NORMAL RAINFALL ANTICIPATED OVER MUCH OF THE EAST-CENTRAL CONUS
DURING WEEK-2 COMBINED WITH AN INCREASED LIKELIHOOD OF EXCESSIVE HEAT 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.
FORECASTER: DANNY BARANDIARAN
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