694
FXUS21 KWNC 231807
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 23 2024
SYNOPSIS: MODEL ENSEMBLES DEPICT A DEEPING MID-LEVEL LOW PRESSURE ACROSS THE
CENTRAL AND EASTERN CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD. MID-LEVEL HIGH
PRESSURE IS FORECAST TO DEVELOP ACROSS WESTERN CANADA AND THE NORTHWESTERN
CONUS AND ALONG WITH MID-LEVEL LOW PRESSURE ACROSS THE ALEUTIAN ISLANDS
INCREASES CHANCES FOR HEAVY PRECIPITATION IN PORTIONS OF SOUTHERN MAINLAND
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 HEAVY PRECIPITATION FOR PORTIONS OF SOUTHERN MAINLAND ALASKA,
SAT-MON, AUG 31-SEP 2.
RISK FOR RAPID ONSET DROUGHT FOR PORTIONS OF THE SOUTHERN PLAINS, AND THE OHIO,
TENNESSEE, AND LOWER AND MIDDLE MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR MONDAY AUGUST 26 - FRIDAY AUGUST 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY AUGUST 31 - FRIDAY SEPTEMBER 06: THE 500-HPA HEIGHTS AND ANOMALIES
FROM THE GEFS, ECENS, AND CANADIAN ENSEMBLES PREDICT A MID-LEVEL TROUGH TO
DEVELOP ACROSS MUCH OF THE EASTERN CONUS BY THE OUTSET OF THE WEEK-2 PERIOD.
THIS SUBSTANTIALLY REDUCES THE RISK FOR EXCESSIVE HEAT RELATIVE TO YESTERDAY
AND NO HEAT RELATED HAZARDS ARE POSTED TODAY. THE GEFS PET REMAINS SLIGHTLY
MORE ROBUST RELATIVE TO THE ECENS IN CHANCES FOR TEMPERATURES TO EXCEED THE
85TH CLIMATOLOGICAL PERCENTILE BUT TEMPERATURES ARE LESS LIKELY TO REACH
HAZARDOUS THRESHOLDS.
A LONG PERIOD OF DRIER THAN NORMAL CONDITIONS ACROSS THE LOWER AND MIDDLE
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, SOUTHERN PLAINS AND SOUTHEAST, HAVE
LED TO DECLINING SOIL MOISTURE VALUES AND LOW STREAM FLOWS. THE WEEK-1 PERIOD
IS LIKELY TO REMAIN DRY AND WARM ACROSS THESE REGIONS ALONG WITH ABOVE-NORMAL
TEMPERATURES IN PARTS OF THE REGION DURING WEEK-2, LEADING TO A RISK OF RAPID
ONSET DROUGHT (ROD) ACROSS THESE AREAS.
HURRICANE GILMA IS AN ACTIVE TROPICAL CYCLONE (TC) LOCATED MORE THAN 1800 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, AND WEAKEN TO A REMNANT LOW IN THE
NEXT 5 DAYS AS IT APPROACHES HAWAII. FOLLOWING TC GILMA, THE NHC IS TRACKING
ANOTHER DISTURBANCE, 1000 MILES FURTHER EAST, 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. ANY
POTENTIAL TC HAS THE POTENTIAL TO BRING HEAVY RAIN, STRONG WINDS, AND DANGEROUS
SURF TO PORTIONS OF HAWAII. AREAS AFFECTED BY RECENT WILDFIRES WOULD ALSO BE AT
ELEVATED RISK FOR LANDSLIDES AND DEBRIS FLOWS.
IN ALASKA, SURFACE AND MID-LEVEL LOW PRESSURE IS FORECAST TO DEVELOP NEAR THE
ALEUTIAN ISLANDS EARLY IN WEEK-2, MEANWHILE, MID-LEVEL HIGH PRESSURE IS
FORECAST OVER BRITISH COLUMBIA. THIS LEADS TO STRONG ONSHORE FLOW ALOFT ACROSS
PARTS OF THE SOUTH-CENTRAL AND SOUTHEASTERN MAINLAND ALASKA COASTAL AREAS. PETS
FROM THE GEFS AND ECENS INDICATE AT LEAST A 20% CHANCE OF PRECIPITATION AMOUNTS
EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 2 INCHES. THEREFORE, A SLIGHT
RISK OF HEAVY PRECIPITATION IS FORECAST FOR AUG 31-SEP 2. SURFACE WINDS MAY
ALSO BE ELEVATED, HOWEVER, THE HIGHEST WINDS ARE MOST LIKELY TO REMAIN OFFSHORE
SO NO ASSOCIATED HAZARD IS POSTED AT THIS TIME.
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.
WITH A MID-LEVEL RIDGE DEVELOPING ACROSS WESTERN NORTH AMERICA, ABOVE-NORMAL
TEMPERATURES ARE FAVORED IN THE EXTENDED RANGE OUTLOOK ACROSS THE PACIFIC
NORTHWEST. THE PETS FROM THE GEFS AND ECENS INDICATE AT LEAST 20% CHANCES FOR
TEMPERATURES TO EXCEED THE 90TH PERCENTILE FOR PORTIONS OF THE INTERIOR
NORTHWEST. HOWEVER, PREDICTED AIR TEMPERATURES ARE UNLIKELY TO REACH HAZARDOUS
THRESHOLDS. AN ADDITIONAL CONCERN ACROSS THE NORTHWESTERN CONUS DUE TO STRONGLY
ABOVE-NORMAL TEMPERATURES AND DRIER THAN NORMAL CONDITIONS MAY BRING ENHANCED
CHANCES FOR WILDFIRE WEATHER ACROSS THE REGION.
FORECASTER: RYAN BOLT
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