271
FXUS21 KWNC 301812
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 30 2023
SYNOPSIS: FORECAST MID-LEVEL HIGH PRESSURE FAVORED OVER MUCH OF THE CONTIGUOUS
U.S. (CONUS) IS EXPECTED TO BRING NEARLY COAST TO COAST ABOVE-NORMAL
TEMPERATURES, WITH AN ELEVATED RISK OF EXCESSIVE HEAT MAINLY OVER THE
SOUTH-CENTRAL CONUS DURING THE PERIOD. STRONG SURFACE PRESSURE GRADIENTS
FAVORED IN THE SOUTHWEST MAY BRING CHANCES FOR EPISODES OF HIGH WINDS, AND
COULD WORSEN ONGOING WILDFIRES THROUGHOUT THE FOUR CORNERS. ENHANCED ONSHORE
FLOW IS EXPECTED TO BRING ABOVE-NORMAL PRECIPITATION ACROSS MANY PARTS OF THE
ALASKA MAINLAND.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL AND SOUTHERN GREAT
PLAINS AND MISSISSIPPI VALLEY, THU-MON, SEP 7-11.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHWEST, GREAT PLAINS,
MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, AND THE SOUTHEAST, THU-WED, SEP 7-13.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MID-ATLANTIC, THU, SEP 7.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE SOUTHWEST, THU-WED, SEP 7-13.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR SATURDAY SEPTEMBER 02 - WEDNESDAY SEPTEMBER 06:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY SEPTEMBER 07 - WEDNESDAY SEPTEMBER 13: LATE IN WEEK-1, THERE IS
GOOD CONSISTENCY ACROSS DYNAMICAL MODELS ADVERTISING A FAIRLY AMPLIFIED 500-HPA
RIDGE OVER MANY AREAS EAST OF THE ROCKIES. BOTH THE GEFS AND ECMWF ENSEMBLES
INITIALLY SHOW THE STRONGEST MID-LEVEL POSITIVE HEIGHT DEPARTURES FAVORED OVER
THE NORTHEASTERN CONUS AT THE START OF WEEK-2, THOUGH THIS FEATURE GRADUALLY
DEAMPLIFIES AS 500-HPA HEIGHTS BEGIN TO BUILD AND EXPAND ACROSS THE
SOUTHWESTERN CONUS THROUGH THE MIDDLE OF THE PERIOD. AS A RESULT, AN EVOLVING
TEMPERATURE ANOMALY PATTERN IS FORECAST WHERE UNSEASONABLY WARM SEPTEMBER
TEMPERATURES ARE EXPECTED TO EASE OVER THE NORTHEASTERN CONUS BY LATE NEXT
WEEK, WHILE CHANCES FOR ABOVE-NORMAL TEMPERATURES ARE EXPECTED TO INCREASE OVER
PARTS OF THE CENTRAL AND SOUTHERN CONUS, SIGNALING THE RETURN OF EXCESSIVE HEAT
CONDITIONS POTENTIALLY AFFECTING THIS PART OF THE COUNTRY DURING THE PERIOD.
TIED TO THE STRONG 500-HPA RIDGING THAT IS EXPECTED TO PERSIST OVER THE
NORTHEASTERN CONUS INTO THE START OF WEEK-2, A SLIGHT RISK OF EXCESSIVE HEAT
REMAINS ISSUED FOR DAY 8 (SEP 7) OVER PARTS OF THE MID-ATLANTIC. WHILE THE GEFS
AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) SUGGEST DAYTIME TEMPERATURES ARE
LIKELY TO STRUGGLE TO EXCEED 95 DEGREES F, BOTH TOOLS CONTINUE TO INDICATE
INCREASED CHANCES (>30%) FOR MAXIMUM TEMPERATURES EXCEEDING THE 90TH PERCENTILE
IN THE HIGHLIGHTED REGION BEFORE COOLER TEMPERATURES ARRIVE BY LATE NEXT WEEK.
AS MUCH OF THE MID-LEVEL RIDGING REMAINS FAVORED TO EXPAND AND BUILD WESTWARD
WITH TIME, PETS MAINTAIN BROAD COVERAGE OF AT LEAST A 20% CHANCE OF MAXIMUM
TEMPERATURES EXCEEDING THE 90TH PERCENTILE THROUGHOUT MUCH OF THE MIDWEST,
GREAT PLAINS AND THE SOUTHERN TIER OF THE CONUS THROUGHOUT THE PERIOD.
THEREFORE, A SLIGHT RISK OF EXCESSIVE HEAT IS CONTINUED FOR THE ENTIRETY OF
WEEK-2, AND IS EXPANDED ACROSS THE SOUTHWEST TO ACCOUNT FOR INCREASED WARM
SIGNALS IN THE PETS.
WITHIN THE BROAD SLIGHT RISK REGION, THE GEFS PET CONTINUES TO LEAN HEAVILY ON
PLACING THE LARGEST HEAT SIGNALS IN THE MIDWEST (ALBEIT TO A NOTICEABLY LESSER
EXTENT COMPARED TO PREVIOUS GUIDANCE), WHEREAS THE ECMWF PET FAVORS A MORE
WESTERLY SOLUTION, DEPICTING 30-40% CHANCES FOR MAXIMUM TEMPERATURES EXCEEDING
THE 90TH PERCENTILE FOCUSED MORE OVER THE GREAT PLAINS AND AREAS MAINLY WEST OF
THE MISSISSIPPI RIVER DURING THE PERIOD. THE OUTLOOK RELIES MORE ON THE LATTER
CALIBRATED GUIDANCE DUE TO A CONSISTENT WARM BIAS NOTED ACROSS THE MIDWEST IN
THE GEFS PET IN ADDITION TO CONSIDERING THE FORECAST PREVAILING MID-LEVEL
PATTERN WHICH FEATURES THE LARGEST POSITIVE HEIGHT DEPARTURES OVER THE FOUR
CORNERS AND GREAT PLAINS. THEREFORE, A MODERATE RISK OF EXCESSIVE HEAT REMAINS
POSTED WITH MUCH OF ITS COVERAGE REDUCED OVER PARTS OF THE MIDDLE AND UPPER
MISSISSIPPI, TENNESSEE AND OHIO VALLEYS COMPARED TO YESTERDAY'S OUTLOOK. THE
MODERATE RISK IS ALSO EXTENDED THROUGH DAY 12 (SEP 11) BASED ON THE PERSISTENCE
OF ANOMALOUS RIDGING IN THE ENSEMBLES, AS WELL AS RAW TEMPERATURE TOOLS WHICH
FEATURE DOUBLE DIGIT TEMPERATURE DEPARTURES LINGERING THROUGH THE MIDDLE OF THE
PERIOD. THIS IS ALSO SUPPORTED BY THE NATIONAL BLEND OF MODELS (NBM) ANALYSIS
DEPICTING AN INCREASED NUMBER OF STATIONS APPROACHING NEAR RECORD DAYTIME
TEMPERATURES THROUGH NEXT WEEKEND OVER THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY.
FOR PRECIPITATION, NO HAZARDS ARE ISSUED OVER THE CONUS. THERE ARE SOME
SIGNALS IN THE ECMWF PET FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE OVER
MID-ATLANTIC AND THE NORTHEAST, LIKELY TIED TO THE PASSAGE OF A FRONTAL
BOUNDARY EARLY IN THE PERIOD. HOWEVER, THIS POTENTIAL IS UNSUPPORTED IN THE
GEFS PET AND THE RAW PRECIPITATION TOTALS AMONG MULTIPLE MODEL ENSEMBLES.
ACROSS THE SOUTHWESTERN CONUS, SURFACE HIGH PRESSURE FAVORED OVER THE COLORADO
PLATEAU AND A POTENTIALLY DEEPENING THERMAL LOW OVER THE SONORAN DESERT INDUCED
BY WARMER THAN NORMAL TEMPERATURES IN THE REGION SUPPORTS THE POTENTIAL FOR
STRENGTHENING PRESSURE GRADIENTS AND EPISODES OF HIGH WINDS. A SLIGHT RISK OF
HIGH WINDS IS ISSUED FOR THE ENTIRETY OF WEEK-2 AND IS EXPANDED TO INCLUDE MORE
OF THE FOUR CORNERS WHERE THERE IS GREATER COVERAGE OF WIND SPEEDS EXCEEDING
THE 85TH PERCENTILE BASED ON THE ECMWF PET. THERE ARE CURRENTLY MULTIPLE
ACTIVE WILDFIRES THROUGHOUT THE FOUR CORNERS, AND THE COMBINATION OF ANOMALOUS
WARMTH, DRYNESS AND ELEVATED WIND POTENTIAL DURING WEEK-2 WOULD LIKELY MAKE
THESE ONGOING INCIDENTS DIFFICULT TO CONTAIN.
A RAPID ONSET DROUGHT (ROD) RISK REMAINS POSTED ACROSS PARTS OF THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY DUE TO THE COMBINATION OF INCREASED 30-DAY
PRECIPITATION DEFICITS, LITTLE TO NO RAINFALL FAVORED IN THE NEXT WEEK, AND
HIGH EVAPOTRANSPIRATION RATES ASSOCIATED WITH THE ABOVE-NORMAL TEMPERATURES.
OVER THE HIGHER LATITUDES OF NORTH AMERICA, ENHANCED ONSHORE FLOW IS FAVORED TO
BRING ABOVE-NORMAL PRECIPITATION OVER THE ALASKA MAINLAND TIED TO ANOMALOUS
RIDGING OVER THE ALEUTIANS AND TROUGHING TO THE NORTH OVER THE BERING SEA.
THERE IS FAIR AGREEMENT BETWEEN THE GEFS AND ECMWF PETS INDICATING 3-DAY
AMOUNTS EXCEEDING THE 85TH PERCENTILE, HOWEVER TOTALS ARE EXPECTED TO REMAIN
BELOW HAZARD THRESHOLDS. ELEVATED WIND SPEEDS ARE ALSO POSSIBLE, THOUGH THE
HIGHEST WINDS ARE EXPECTED TO REMAIN OFFSHORE.
FORECASTER: NICK NOVELLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page