384
FXUS21 KWNC 101814
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 10 2024
SYNOPSIS: MULTIPLE MODEL ENSEMBLES DEPICT A 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 FOUR CORNERS, ROCKIES, AND GREAT PLAINS 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, WED-SAT, SEP 18-21.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE MID-ATLANTIC AND SOUTHEAST COASTS
WED-SAT, SEP 18-21.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY,WED-SAT, SEP 18-21.
SLIGHT RISK FOR EPISODES OF HIGH WINDS FOR A LARGE PORTION OF THE SOUTHWESTERN
CONUS, SOUTHERN AND CENTRAL ROCKIES, AND CENTRAL AND NORTHERN PLAINS, WED-FRI,
SEP 18-20.
DETAILED SUMMARY
FOR FRIDAY SEPTEMBER 13 - TUESDAY SEPTEMBER 17:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY SEPTEMBER 18 - TUESDAY SEPTEMBER 24: 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
SOUTHWESTERN CONUS, 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 AND DETERMINISTIC GUIDANCE AS WELL. THEREFORE, A
SLIGHT RISK OF HIGH WINDS IS POSTED FOR SEP 18-20 ACROSS MUCH OF THE
SOUTHWESTERN CONUS, CENTRAL ROCKIES, AND PLAINS. ACROSS THE SOUTHERN PLAINS,
DEW POINTS ARE FORECAST BY THE DYNAMIC ENSEMBLES TO BE BELOW-NORMAL AND WOULD
SUPPORT INCREASED CHANCES FOR RED FLAG WEATHER IN THESE AREAS. WHILE
TEMPERATURES ARE FAVORED TO BE BELOW-NORMAL IN PORTIONS OF THE SOUTHWEST AND
SOUTHERN CALIFORNIA HIGH WINDS MAY EXACERBATE EXISTING FIRES IN THE REGION.
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 40% 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 18-21.
IN THE SOUTHEASTERN CONUS THE REMNANT ENERGY OF 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
CHARLESTON AREA FOR SEP 18-21. THERE COULD ALSO BE A CORRESPONDING THREAT FOR
HIGH WINDS ACROSS THE COASTAL REGIONS OF THE SOUTHEAST WITH STRONG 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 18-21. 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 THE WEST, TEMPERATURES ARE FORECAST TO BE BELOW-NORMAL. PETS INDICATE A
GREATER THAN 20% CHANCE OF TEMPERATURES FALLING BELOW THE 15TH PERCENTILE.
HOWEVER, REGIONS THAT ARE LIKELY TO BE NEAR 32 FOR A FREEZE OR BELOW 40 DEG F
FOR THE POTENTIAL OF FROST ARE LIKELY TO BE IN ELEVATED REGIONS WITH LIMITED
HAZARDOUS IMPACT. THEREFORE, NO CORRESPONDING HAZARD IS POSTED TODAY.
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.
FORECASTER: RYAN BOLT
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