977
FXUS21 KWNC 101859
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 10 2023
SYNOPSIS: MID-LEVEL HIGH PRESSURE IS ANTICIPATED TO PERSIST, BUT SLOWLY
DIMINISH IN STRENGTH, OVER THE SOUTHERN CONTIGUOUS U.S. (CONUS) DURING WEEK-2,
LEADING TO THE POTENTIAL FOR EXCESSIVE HEAT ACROSS THE SOUTHERN CONUS. SURFACE
LOW PRESSURE OVER SOUTHERN ARIZONA AND HIGH PRESSURE OVER COLORADO ENHANCES THE
RISK FOR HIGH WINDS OVER PARTS OF THE SOUTHWESTERN CONUS. A POTENTIAL MOISTURE
SURGE FROM TROPICAL ACTIVITY FAVORED IN THE EAST PACIFIC INCREASES THE RISK FOR
HEAVY PRECIPITATION AND FLASH FLOODING ACROSS PARTS OF THE DESERT SOUTHWEST.
THE EXCESSIVE HEAT POTENTIAL COUPLED WITH ABNORMALLY DRY CONDITIONS ACROSS THE
SOUTH-CENTRAL CONUS SUPPORTS THE ELEVATED POTENTIAL FOR RAPID ONSET DROUGHT
ACROSS PARTS OF TEXAS AND THE LOWER MISSISSIPPI VALLEY.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE SOUTH-CENTRAL CONUS, FRI, AUG
18.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE WESTERN CONUS, FRI, AUG 18.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN CONUS AND COASTAL
MID-ATLANTIC, FRI-THU, AUG 18-24.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE DESERT SOUTHWEST AND THE FOUR
CORNERS, FRI-MON, AUG 18-21.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE DESERT SOUTHWEST, SAT-MON,
AUG 19-21.
FLOODING POSSIBLE FOR PARTS OF THE DESERT SOUTHWEST.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR SUNDAY AUGUST 13 - THURSDAY AUGUST 17:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 18 - THURSDAY AUGUST 24: ENSEMBLE MODEL SOLUTIONS FROM THE
GEFS, ECMWF, AND CMCE ALL DEPICT WEAKENING MID-LEVEL RIDGING ACROSS THE WESTERN
AND SOUTHERN CONUS DURING WEEK-2. HOWEVER, STRONG SIGNALS IN BOTH THE GEFS AND
ECENS PROBABILISTIC EXTREMES TOOLS (PETS) EARLY IN WEEK-2 STILL SUPPORT A
MODERATE RISK OF EXCESSIVE HEAT ACROSS PORTIONS OF THE SOUTHERN PLAINS AND
LOWER MISSISSIPPI VALLEY, AUG 18, WITH BOTH PETS INDICATING AT LEAST A 40
PERCENT CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE OF THE
HISTORICAL DISTRIBUTION. AN ENCOMPASSING SLIGHT RISK OF EXCESSIVE HEAT IS
MAINTAINED THROUGHOUT THE ENTIRETY OF WEEK-2 ACROSS THE SOUTHERN TIER OF THE
CONUS, EXTENDING FROM WESTERN ARIZONA EASTWARD TO THE SOUTHEAST AND NORTHWARD
ALONG THE MID-ATLANTIC COAST. THE SLIGHT RISK OF EXCESSIVE HEAT ACROSS THE
SOUTHERN TIER IS FORECAST TO SHRINK IN COVERAGE, BECOMING CONFINED TO THE
SOUTHEAST, GULF COAST, AND RIO GRANDE VALLEY BY THE END OF WEEK-2. A SLIGHT
RISK OF EXCESSIVE HEAT IS ALSO POSTED ACROSS THE PACIFIC NORTHWEST, GREAT
BASIN, AND PARTS OF THE DESERT SOUTHWEST, AUG 18. THE GEFS PET MAINTAINS THE
STRONGEST HEAT SIGNALS ACROSS THE PACIFIC NORTHWEST. HOWEVER, THE SIGNALS IN
THE GEFS PET LINGER AN EXTRA DAY, COMPARED TO THE ECMWF, THEREBY ADDING SOME
UNCERTAINTY IN THE END OF THE HEAT IN THE PACIFIC NORTHWEST. IN ADDITION TO THE
EXCESSIVE DAYTIME HIGH TEMPERATURES, THE NATIONAL BLEND OF MODELS INDICATES THE
POTENTIAL FOR MUCH ABOVE NORMAL LOW TEMPERATURES IN SEVERAL LOCATIONS ACROSS
THE WEST AND SOUTHERN U.S., BECOMING CONFINED PREDOMINANTLY TO THE SOUTHERN
TIER BY AUG 20.
TROPICAL CYCLONE ACTIVITY IN THE EAST PACIFIC IS FORECAST TO INCREASE OVER THE
NEXT TWO WEEKS, INCREASING THE LIKELIHOOD FOR A MOISTURE SURGE FROM THE GULF OF
CALIFORNIA INTO THE FOUR CORNERS REGION DURING THE MIDDLE OF WEEK-2. MODEL
SOLUTIONS OF THIS SURGE CURRENTLY LIMIT ITS NORTHERN EXTENT AND FORECAST
RAINFALL TOTALS. HOWEVER, PETS AGREE WELL SPATIALLY IN INDICATING AT LEAST A 20
PERCENT CHANCE OF EXCEEDING THE 85TH PERCENTILE OF THE HISTORICAL DISTRIBUTION
AND 0.5 INCHES OF RAINFALL. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION IS
POSTED ACROSS PARTS OF THE SONORAN DESERT AND ALONG THE MOGOLLON RIM, AUG
19-21, COINCIDING WITH THE POTENTIAL GULF SURGE EVENT. BEYOND THAT TIME, MODELS
DO INDICATE A MORE FAVORABLE MONSOON CIRCULATION PATTERN THAT COULD SUPPORT
ADDITIONAL RAINFALL ACTIVITY. ASSOCIATED WITH THE SLIGHT RISK OF HEAVY
PRECIPITATION, FLOODING AND/OR FLASH FLOODING IS ALSO POSSIBLE ACROSS AREAS IN
THE SOUTHWESTERN CONUS DURING WEEK-2.
THE THERMAL LOW OVER THE DESERT SOUTHWEST AND SURFACE HIGH PRESSURE OVER THE
COLORADO PLATEAU FAVOR AN ENHANCED PRESSURE GRADIENT ACROSS PARTS OF THE DESERT
SOUTHWEST AND FOUR CORNERS. THEREFORE, A SLIGHT RISK OF HIGH WINDS IS POSTED
AUG 18-21. THE ECMWF AND CMCE PETS INDICATE STRONGER SIGNALS THAN THE GEFS,
INDICATING AT LEAST A 20 PERCENT CHANCE OF WIND SPEEDS EXCEEDING THE 85TH
PERCENTILE OF THE HISTORICAL DISTRIBUTION, WITH SIGNALS DIMINISHING BEYOND AUG
21.
ABNORMAL DRYNESS COUPLED WITH THE RISK OF EXCESSIVE HEAT WARRANTS A RAPID ONSET
DROUGHT RISK ACROSS PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.
FORECASTER: ADAM HARTMAN
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