780
FXUS21 KWNC 081817
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 08 2024
SYNOPSIS: FLOODING FROM TROPICAL STORM DEBBY MAY LINGER INTO THE EARLY PORTIONS
OF WEEK-2 ALONG THE EASTERN SEABOARD. EXCESSIVE HEAT IS LIKELY TO IMPACT
PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY BENEATH MID-LEVEL
HIGH PRESSURE CENTERED ACROSS THE SOUTH-CENTRAL CONTIGUOUS U.S. (CONUS).
ABOVE-NORMAL TEMPERATURES AND BELOW-NORMAL PRECIPITATION ALONG WITH LIMITED
ANTECEDENT RAINFALL LEADS TO A RISK OF RAPID ONSET DROUGHT FOR PORTIONS OF THE
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHEAST, LOWER
MISSISSIPPI VALLEY, AND SOUTHERN PLAINS, FRI-SAT, AUG 16-17.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY AND SOUTHEAST, FRI-TUE, AUG 16-20.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE FLORIDA PENINSULA, FRI, AUG
16.
RAPID ONSET DROUGHT RISK FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY
FLOODING POSSIBLE RISK FOR MUCH OF THE EASTERN SEABOARD.
DETAILED SUMMARY
FOR SUNDAY AUGUST 11 - THURSDAY AUGUST 15:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 16 - THURSDAY AUGUST 22: 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. MID-LEVEL TROUGHS ARE EXPECTED ALONG BOTH THE EAST
AND WEST COASTS. AS THE WEEK PROGRESSES, THE TROUGHS NEAR THE COASTS ARE
FORECAST 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 ARE EXPECTED TO BE OVER OR NEAR THE EASTERN AND WESTERN PORTIONS OF
NORTH AMERICA WITH A MID-LEVEL RIDGE EXTENDING FROM THE EASTERN FOUR CORNERS
REGION NORTHWARD ROUGHLY ALONG THE FRONT RANGE OF THE ROCKIES NORTHWARD INTO
NORTH-CENTRAL CANADA. IN ALASKA, MID-LEVEL TROUGHING IS GENERALLY FAVORED AMONG
THE TOOLS THROUGHOUT MUCH OF THE PERIOD.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ALONG THE MID-LEVEL RIDGE AXIS THROUGH
THE GREAT PLAINS, WITH THE HOTTEST WEATHER EXPECTED ACROSS THE SOUTHERN HALF OF
THE GREAT PLAINS AND LOWER MISSISSIPPI VALLEY. THE CENTER OF THE MID-LEVEL
RIDGE IS EXPECTED TO MOVE VERY LITTLE UNTIL THE END OF THE PERIOD. THE
PROBABILISTIC EXTREMES TOOLS (PETS) FOR THE GEFS AND ECENS SHOW AN AREA OF
GREATER THAN 30% CHANCES OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE
IN THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY. THE PETS ARE GENERALLY
WEAKER RELATIVE TO YESTERDAY, PARTICULARLY ACROSS THE NORTHERN AND EASTERN
AREAS OF THE AREA OF CONCERN. HOWEVER, THE SKILL WEIGHTED BIAS-CORRECTED
APPARENT TEMPERATURE TOOL FORECASTS HEAT INDICES TO EXCEED 110 DEG F ACROSS
MUCH OF THE REGION, AND ARE GENERALLY WARMER RELATIVE TO YESTERDAY. THEREFORE,
A MODERATE RISK OF EXCESSIVE HEAT REMAINS POSTED FOR AUG 16-17 ACROSS PORTIONS
OF THE LOWER MISSISSIPPI VALLEY AND SOUTHERN PLAINS. A BROADER SLIGHT RISK IS
MAINTAINED THROUGH MUCH OF THE WEEK-2 PERIOD WITH CONTINUED CHANCES FROM THE
PETS FOR TEMPERATURES EXCEEDING THE 85TH PERCENTILE ACROSS MUCH OF THE
SOUTHEASTERN CONUS.
BELOW-NORMAL RAINFALL ANTICIPATED OVER MUCH OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY DURING WEEK-2, COMBINED WITH INCREASED LIKELIHOOD OF
EXCESSIVE HEAT AND BELOW-NORMAL 30-DAY RAINFALL, RESULTS IN AN ELEVATED RISK OF
RAPID ONSET DROUGHT. TODAY, AN ADDITIONAL AREA OF RAPID ONSET DROUGHT RISK IS
PLACED OVER PORTIONS OF SOUTHWEST ARKANSAS, NORTHEAST LOUISIANA, AND CENTRAL
MISSISSIPPI SUPPORTED BY DECLINING SOIL MOISTURE VALUES AND DRY CONDITIONS
FAVORED OVER THE NEXT TWO WEEKS. THE AREA IN THE SOUTHERN PLAINS HAS SEEN
DROUGHT CONTINUE TO DEVELOP ACROSS THE REGION BUT HAS BEEN EXTENDED EAST ALONG
THE RED RIVER TO OVER SOUTHEAST OKLAHOMA INTO EASTERN ARKANSAS. MUCH OF THIS
REGION IS ALREADY IDENTIFIED AS ABNORMALLY DRY (D0) ON THE U.S. DROUGHT MONITOR.
IN FLORIDA, THE PETS FROM THE GEFS AND ECENS INDICATE 20 TO 30% CHANCES OF
TEMPERATURES EXCEEDING THE 85TH PERCENTILE, WITH RAW ENSEMBLE TEMPERATURES FROM
THE GEFS AND ECENS APPROACHING 95 DEG F WHICH IN COMBINATION WITH HIGH DEW
POINTS MAY BRING HAZARDOUS HEAT TO THE AREA. THEREFORE, A SLIGHT RISK OF
EXCESSIVE HEAT IS POSTED FOR AUG 16 FOR PORTIONS OF THE FLORIDA PENINSULA.
DURING WEEK-1, EXCESSIVE RAINFALL IS EXPECTED IN ASSOCIATION WITH SLOW-MOVING
TROPICAL STORM 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 MAY CONTINUE IN THE AREAS EXPECTED TO BE MOST SEVERELY
AFFECTED BY DEBBY AND ASSOCIATED EXCESSIVE RAINFALL DURING WEEK-1, ALONG WITH
SOME AREAS OF VERY WET ANTECEDENT CONDITIONS IN NEW ENGLAND. WATER MODELS FROM
THE NATIONAL WATER CENTER (NWC) HAVE INCREASED CONFIDENCE FOR HIGH STREAM AND
RIVER FLOWS ACROSS THE MID-ATLANTIC AND NEW ENGLAND EARLY IN WEEK-2. 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.
IN THE SOUTHWEST, THERE ARE SOME MORE ENHANCED SIGNALS FOR HEAVY PRECIPITATION
IN THE ECENS PET, HOWEVER, THE GEFS IS YET TO SHOW THIS SIGNAL. THE ECENS PET
REMAINS ALONE IN ITS FORECAST AND DUE TO LIMITED CONSISTENCY AMONG THESE TOOLS,
NO ASSOCIATED HAZARD IS POSTED TODAY. HOWEVER, THIS WOULD BE CONSISTENT WITH
THE MID-LEVEL RIDGE ACROSS THE CENTRAL CONUS RETROGRADING BACK TOWARDS THE
WESTERN CONUS AND BEARS CONTINUED WATCHING.
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: RYAN BOLT
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