940
FXUS21 KWNC 051839
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 05 2024
SYNOPSIS: MID-LEVEL HIGH PRESSURE CENTERED OVER THE SOUTHERN GREAT PLAINS WILL
SLOWLY DRIFT WESTWARD, CREATING A SLIGHT RISK OF EXCESSIVE HEAT THROUGHOUT
WEEK-2 OVER PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHERN PLAINS. THE
ABNORMAL HEAT COMBINED WITH DEFICIENT RAINFALL IN PART OF THIS REGION ENHANCES
THE RISK FOR RAPID-ONSET DROUGHT OVER MUCH OF OKLAHOMA AND NORTHERN TEXAS.
FARTHER EAST, EXCESSIVE RAINFALL ASSOCIATED WITH HURRICANE DEBBY DURING THE
NEXT SEVERAL DAYS HAS THE POTENTIAL TO PRODUCE MAJOR FLOODING ALONG MUCH OF THE
ATLANTIC SEABOARD AND NEW ENGLAND WHICH IS LIKELY TO PERSIST INTO WEEK-2.
HAZARDS
SLIGHT RISK OF EXCESSIVE HEAT ACROSS MUCH OF THE CENTRAL AND SOUTHERN PLAINS
AND LOWER MISSISSIPPI VALLEY, TUE-MON, AUG 13-19, 2024.
FLOODING POSSIBLE OVER MUCH OF THE ATLANTIC COASTAL PLAIN AND PIEDMONT, AND
PORTIONS OF NEW ENGLAND.
RAPID ONSET DROUGHT POSSIBLE OVER PART OF THE SOUTHERN PLAINS.
DETAILED SUMMARY
FOR THURSDAY AUGUST 08 - MONDAY AUGUST 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY AUGUST 13 - MONDAY AUGUST 19: MODELS GENERALLY AGREE ON THE
EVOLUTION OF THE MID-LEVEL PATTERN ACROSS NORTH AMERICA DURING WEEK-2. THE
PERIOD STARTS WITH A RIDGE AXIS EXTENDING SOUTHWARD FROM NORTH-CENTRAL CANADA
INTO THE SOUTHERN PLAINS, WITH THE GREATEST 500-HPA HEIGHTS ON THE SOUTHERN END
OF THE AXIS. MEANWHILE, MID-LEVEL TROUGHS ARE EXPECTED ACROSS BOTH THE EASTERN
AND WESTERN FRINGES OF CANADA AND THE CONTIGUOUS UNITED STATES (CONUS). AS THE
WEEK PROGRESSES, THE TROUGHS NEAR THE COASTS ARE EXPECTED TO SLOWLY WEAKEN
WHILE THE MID-CONTINENT RIDGE MAINTAINS ITS STRENGTH AND RETROGRADES SLIGHTLY.
BY THE END OF WEEK-2, WEAK REMNANTS OF THE MID-LEVEL TROUGHS SHOULD BE OVER OR
NEAR THE EASTERN AND WESTERN PORTIONS OF NORTH AMERICA WHILE THE MID-LEVEL
RIDGE AXIS NEAR THE MIDDLE OF THE CONTINENT HAS DRIFTED WESTWARD, EXTENDING
FROM THE EASTERN FOUR CORNERS REGION NORTHWARD ROUGHLY ALONG THE FRONT RANGE OF
THE ROCKIES NORTHWARD INTO NORTH-CENTRAL CANADA.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ALONG THE MID-LEVEL RIDGE AXIS THROUGH
THE PLAINS, WITH THE HOTTEST WEATHER EXPECTED ACROSS THE SOUTHERN HALF OF THE
GREAT PLAINS, WHERE THERE IS A SLIGHT RISK OF EXCESSIVE HEAT. WHILE WARMER THAN
NORMAL CONDITIONS ARE HIGHLY LIKELY, IS IT LESS CERTAIN WHETHER TEMPERATURES
WILL REACH HAZARDS THRESHOLDS. RIGHT NOW, ENSEMBLE MEANS AGREE THAT THE BEST
CHANCES FOR SUCH CONDITIONS ROUGHLY EXTEND FROM THE SOUTHERN HIGH PLAINS
EASTWARD INTO THE LOWER MISSISSIPPI VALLEY, REACHING AS FAR NORTH AS SOUTHERN
KANSAS AND NORTHWESTERN ARKANSAS. WITH THE CENTER OF THE MID-LEVEL RIDGE MOVING
LITTLE DURING THE PERIOD, THE RISK OF EXCESSIVE HEAT IN THIS AREA SHOULD
PERSIST THROUGH ALL OF WEEK-2. FROM THE SOUTHEASTERN GREAT PLAINS INTO THE
LOWER MISSISSIPPI VALLEY, RELATIVELY HIGH DEW POINTS ARE EXPECTED TO INCREASE
HEAT INDICES POTENTIALLY INTO THE EXCESSIVE HEAT RANGE. FARTHER WEST, THE
ACTUAL TEMPERATURES ARE EXPECTED TO APPROACH OR EXCEED THE EXCESSIVE HEAT
THRESHOLD.
THE PROBABILISTIC EXTREMES TOOLS (PETS) FOR ALL THREE ENSEMBLES SHOW ENHANCED
CHANCES FOR MAXIMUM TEMPERATURES TO EXCEED THE 85TH PERCENTILE IN THE SOUTHERN
PLAINS AND SOME ADJACENT AREAS AT THE START OF WEEK-2, AND THE PETS DERIVED
FROM THE ECENS AND GEFS KEEP THE ELEVATED RISK IN PLACE FOR THE ENTIRE WEEK.
ONLY THE GEFS PET, HOWEVER, SHOWS ODDS OF HIGH TEMPERATURES ABOVE THE 85TH
PERCENTILE EXCEEDING 40 PERCENT, AND ONLY FOR THE FIRST TWO DAYS OF THE PERIOD.
THE ECENS PET KEEPS THE ODDS FOR EXCESSIVE HEAT CLOSER TO 30 PERCENT, AND THE
CANADIAN ENSEMBLE PET ELIMINATES THE THREAT COMPLETELY BY MIDWEEK. THE SLIGHT
RISK OF EXCESSIVE HEAT REPRESENTS A COMPROMISE OF ALL THESE INDICATORS.
BELOW-NORMAL RAINFALL IS ANTICIPATED OVER MUCH OF THE SOUTHERN PLAINS DURING
WEEK-2, AND IN AREAS WHERE THIS COINCIDES WITH THE RISK OF EXCESSIVE HEAT AND
WITH SIGNIFICANTLY BELOW-NORMAL 30-DAY RAINFALL, THERE IS AN ELEVATED RISK OF
RAPID ONSET DROUGHT. MORE SPECIFICALLY, THIS COVERS AN AREA FROM THE RED RIVER
(OF THE SOUTH) VALLEY WESTWARD, INCLUDING MUCH OF OKLAHOMA AND NORTHERN TEXAS.
MUCH OF THIS REGION IS ALREADY IDENTIFIED AS ABNORMALLY DRY (D0) ON THE U.S.
DROUGHT MONITOR.
DURING WEEK-1, EXCESSIVE RAINFALL IS EXPECTED IN ASSOCIATION WITH SLOW-MOVING
HURRICANE DEBBY. CURRENTLY, A LARGE AREA OF FLOODING IS POSSIBLE IN THE
SHORT-TERM FROM CENTRAL FLORIDA NORTHWARD INTO NEW ENGLAND. FOR THE WEEK-2
PERIOD, FLOODING IS EXPECTED TO CONTINUE IN THE AREAS EXPECTED TO BE MOST
SEVERELY AFFECTED BY HURRICANE DEBBY AND ASSOCIATED EXCESSIVE RAINFALL DURING
WEEK-1, ALONG WITH SOME AREAS OF VERY WET ANTECEDENT CONDITIONS IN NORTHERN NEW
ENGLAND. AS A RESULT, A LARGE AREA OF POSSIBLE WEEK-2 FLOODING EXTENDS FROM
NORTHEASTERN FLORIDA NORTHWARD ALONG MOST OF THE COASTAL PLAIN AND PIEDMONT OF
THE ATLANTIC SEABOARD, IN ADDITION TO MUCH OF NEW ENGLAND. FURTHER EXPANSION OF
THE REGION WITH POTENTIAL WEEK-2 FLOODING MAY BE NECESSARY AS THE EVOLUTION OF
HURRICANE DEBBY BECOMES MORE CERTAIN LATER THIS WEEK.
WITH A MID-LEVEL TROUGH TO ITS WEST AND A LARGE 500-HPA POSITIVE ANOMALY CENTER
TO THE EAST, UNSETTLED CONDITIONS ARE EXPECTED ACROSS MOST OF ALASKA DURING
WEEK-2, WITH UNUSUALLY HEAVY PRECIPITATION MOST LIKELY IN WESTERN PARTS OF THE
MAINLAND. CURRENTLY, PRECIPITATION AND WIND ARE EXPECTED TO REMAIN BELOW
HAZARDS THRESHOLDS, BUT THE REGION WILL NEED TO BE MONITORED FOR ANY INCREASE
IN PRECIPITATION SHOWN BY THE MODELS.
FORECASTER: RICH TINKER
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