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FXUS21 KWNC 091848
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 09 2024
SYNOPSIS: MULTIPLE MODEL ENSEMBLES DEPICT A WEAKENING MID-LEVEL LOW PRESSURE
ACROSS THE WESTERN CONTIGUOUS U.S. (CONUS) EARLY IN THE PERIOD. ONE OR MORE
MID-LATITUDE CYCLONES MAY DEVELOP IN THE LEE OF THE TROUGH AND ROCKIES,
SUPPORTING ENHANCED RISK FOR HIGH WINDS TO THE GREAT PLAINS AND ROCKIES WHILE
BRINGING INCREASED CHANCES FOR HEAVY PRECIPITATION TO PORTIONS OF THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY. MID-LEVEL HIGH PRESSURE IS FORECAST ACROSS
EASTERN CANADA EXTENDING INTO THE NORTHEASTERN CONUS BRINGING ABOVE-NORMAL
TEMPERATURES THAT ARE UNLIKELY TO REACH HAZARDOUS CRITERIA. THE REMNANTS OF
TROPICAL STORM FRANCINE IN THE SOUTHEASTERN CONUS MAY BRING UNSETTLED WEATHER
TO THE SOUTHERN ATLANTIC COAST.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE COASTAL MID-ATLANTIC AND
SOUTHEAST, TUE-FRI, SEP 17-20.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST COASTS
TUE-FRI, SEP 17-20.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY, TUE-FRI, SEP 17-20.
SLIGHT RISK FOR EPISODES OF HIGH WINDS FOR A LARGE PORTION OF THE SOUTHERN AND
CENTRAL ROCKIES, AND CENTRAL AND NORTHERN PLAINS, TUE-THU, SEP 17-19.
DETAILED SUMMARY
FOR THURSDAY SEPTEMBER 12 - MONDAY SEPTEMBER 16:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY SEPTEMBER 17 - MONDAY SEPTEMBER 23: A MID-LEVEL TROUGH AND
ASSOCIATED NEGATIVE 500-HPA HEIGHT ANOMALIES IS FORECAST ACROSS THE WESTERN
CONUS EARLY IN THE WEEK-2 PERIOD. ONE OR MORE EXTRA-TROPICAL CYCLONES MAY
DEVELOP IN THE LEE OF THE ROCKIES AFTER EJECTING FROM THE MID-LATITUDE TROUGH
AND TRACK NORTHEAST ACROSS THE PLAINS. THIS TROUGH AND MID-LATITUDE CYCLONE(S)
PATTERN MAY INCREASE CHANCES FOR HIGH WINDS ACROSS A BROAD PORTION OF THE
ROCKIES AND GREAT PLAINS EARLY IN THE WEEK-2 PERIOD. THE PROBABILISTIC EXTREMES
TOOLS (PETS) FROM THE GEFS AND ECENS INDICATE INCREASED (>20%) CHANCES FOR
WINDS TO EXCEED THE 85TH PERCENTILE. THIS IS SUPPORTED BY SOME OF THE RAW
ENSEMBLE TOOLS AS WELL. THEREFORE, A SLIGHT RISK OF HIGH WINDS IS POSTED FOR
SEP 17-19 ACROSS MUCH OF THE FOUR CORNERS, CENTRAL ROCKIES, AND PLAINS. ACROSS
THE SOUTHERN PORTIONS OF THIS REGION, DEW POINTS ARE FORECAST BY THE DYNAMIC
ENSEMBLES TO BE BELOW-NORMAL. THIS WOULD SUPPORT INCREASED CHANCES FOR RED FLAG
WEATHER IN THESE AREAS. IN THE NORTHERN PLAINS AND UPPER-MISSISSIPPI VALLEY,
ENHANCED PRECIPITATION IS POSSIBLE ASSOCIATED WITH THE SURFACE LOW PRESSURE
AREA(S) AS THEY MOVE NORTHEASTWARD FROM THE ROCKIES. THIS IS SUPPORTED BY PETS
INDICATING ELEVATED CHANCES (>30%) OF 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE
85TH PERCENTILE. RAW GUIDANCE FROM THE ECENS SHOWS A GREATER THAN 20% CHANCE OF
3 DAY PRECIPITATION EXCEEDING 1 INCH AS WELL. SOME OF THIS PRECIPITATION MAY
COME IN THE FORM OF THUNDERSTORM ACTIVITY ALONG THE ASSOCIATED FRONTAL BOUNDARY
OF THE LOW-PRESSURE SYSTEM. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS
POSTED FOR SEP 17-20.
IN THE SOUTHEASTERN CONUS THE REMNANT ENERGY OF A TROPICAL STORM FRANCINE,
CURRENTLY IN THE GULF OF MEXICO WILL BRING NEAR- TO BELOW-NORMAL 500-HPA
HEIGHTS TO THE REGION. MUCH OF THE ENERGY LOOKS TO BECOME STATIONARY JUST OFF
AND ALONG THE SOUTHEASTERN ATLANTIC COAST AND MAY BRING CHANCES FOR HEAVY
PRECIPITATION BACK INTO THE PORTIONS OF THE COASTAL CAROLINAS AND THE TIDEWATER
REGION OF VIRGINIA. THIS IS SUPPORTED BY BOTH RAW ENSEMBLE GUIDANCE AND PETS
SHOWING CHANCES FOR 3-DAY PRECIPITATION AMOUNTS TO EXCEED THE 85TH PERCENTILE
AND 1 INCH. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR
COASTAL PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST FROM THE DELMARVA TO THE
JACKSONVILLE AREA FOR SEP 17-20. THERE COULD ALSO BE A CORRESPONDING THREAT FOR
HIGH WINDS ACROSS THE COASTAL REGIONS OF THE SOUTHEAST WITH STRONG HIGH SURFACE
HIGH PRESSURE FORECAST OVER NEW ENGLAND THAT WOULD BRING STRONG ONSHORE WINDS
INTO THE SOUTHEAST. ANY TROPICAL OR SUB-TROPICAL DEVELOPMENT OF LOW PRESSURE
ACROSS THE COASTAL REGIONS WOULD ALSO SUPPORT A SLIGHT RISK OF HIGH WINDS FOR
THE SOUTHEAST COAST. THEREFORE, A CORRESPONDING SLIGHT RISK OF HIGH WINDS IS
POSTED FOR SEP 17-20. BY THE END OF THE PERIOD, TOOLS ARE MORE DIVERGENT ON
WHETHER THE PATTERN WILL REMAIN STATIONARY OR BECOME MORE PROGRESSIVE AND
UNCERTAINTY IN THE PATTERN INCREASES.
STRONG POSITIVE 500-HPA HEIGHT ANOMALIES FORECAST ACROSS EASTERN CANADA SPILL
INTO THE NORTHEASTERN CONUS BRINGING WEAK RIDGING TO THE REGION AND
ABOVE-NORMAL TEMPERATURES. HOWEVER, THESE TEMPERATURES ARE UNLIKELY TO REACH
HAZARDOUS THRESHOLDS WITH CLIMATOLOGICAL TEMPERATURES RAPIDLY FALLING DURING
THE SECOND HALF OF SEPTEMBER.
IN ALASKA, ABOVE-NORMAL PRECIPITATION SEEMS MOST LIKELY ACROSS SOUTHERN
PORTIONS OF THE STATE. HOWEVER, REFORECAST CALIBRATED TOOLS INDICATE 3-DAY
PRECIPITATION AMOUNTS THAT ARE UNLIKELY TO REACH HAZARDOUS THRESHOLDS FOR EARLY
FALL. THEREFORE, NO CORRESPONDING HAZARD IS POSTED AT THIS TIME.
TROPICAL STORM FRANCINE IS FORECAST TO MOVE NORTH THROUGH THE MISSISSIPPI
VALLEY AND BRING SUBSTANTIAL AMOUNTS OF PRECIPITATION AS FAR NORTH AS THE OHIO
RIVER DURING WEEK-1. THIS REDUCES CHANCES FOR RAPID ONSET DROUGHT (ROD) ACROSS
THE REGION AND NO CORRESPONDING HAZARD IS POSTED TODAY.
FORECASTER: RYAN BOLT
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