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FXUS21 KWNC 051820
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 05 2026
SYNOPSIS: PERSISTENT MID-LEVEL HIGH PRESSURE OVER THE GREAT PLAINS FAVORS THE
CONTINUED POTENTIAL FOR EXTREME HEAT FOR THE SOUTH-CENTRAL AND SOUTHEASTERN
CONTIGUOUS U.S. (CONUS) THROUGHOUT THE WEEK-2 FORECAST PERIOD. AN ENHANCED
SOUTHWEST MONSOON MAY RESULT IN PERIODS OF HEAVY PRECIPITATION AND LOCALIZED
FLASH FLOODING. MID-LEVEL LOW PRESSURE OVER HUDSON BAY ALONG WITH ABUNDANT GULF
MOISTURE INCREASES THE POTENTIAL FOR HEAVY PRECIPITATION FOR THE OHIO VALLEY
AND MIDWEST.
HAZARDS
MODERATE RISK OF EXTREME HEAT FOR PORTIONS OF THE SOUTHERN AND CENTRAL PLAINS,
AND THE LOWER MISSISSIPPI VALLEY, THU-SUN, AUG 13-16.
SLIGHT RISK OF EXTREME HEAT FOR MUCH OF THE SOUTH-CENTRAL AND SOUTHEASTERN
CONUS, THU-WED, AUG 13-19.
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST AND
SOUTHERN GREAT BASIN, THU-SAT, AUG 13-15.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE DESERT SOUTHWEST, SOUTHERN GREAT
BASIN, AND CENTRAL AND SOUTHERN ROCKIES, THU-WED, AUG 13-19.
SLIGHT RISK OF HEAVY PRECIPITATION FROM THE UPPER AND MIDDLE MISSISSIPPI VALLEY
TO THE OHIO VALLEY AND CENTRAL APPALACHIANS, THU-SAT, AUG 13-15.
FLOODING POSSIBLE FOR PORTIONS OF THE DESERT SOUTHWEST AND SOUTHERN GREAT BASIN.
RAPID ONSET DROUGHT (ROD) POSSIBLE FOR PORTIONS OF THE SOUTHERN AND CENTRAL
PLAINS AND THE LOWER AND MIDDLE MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR SATURDAY AUGUST 08 - WEDNESDAY AUGUST 12:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY AUGUST 13 - WEDNESDAY AUGUST 19: MULTIPLE MODEL ENSEMBLES DEPICT
ANOMALOUS MID-LEVEL RIDGING PERSISTING OVER THE SOUTHEASTERN CONUS THROUGHOUT
WEEK-2, WITH A CLOSED 594-DM HEIGHT CONTOUR SETTLING OVER THE LOWER MISSISSIPPI
VALLEY BY THE MIDDLE OF THE FORECAST PERIOD AND MERGING WITH THE SUBTROPICAL
RIDGE OVER THE CARIBBEAN, THEREBY INCREASING THE POTENTIAL FOR EXTREME HEAT
ALONG THE GULF COAST. GENERALLY SOUTHERLY FLOW OFF THE GULF OF AMERICA IS
FAVORED TO BOOST DEW POINTS EAST OF THE ROCKIES, RESULTING IN POTENTIALLY
HAZARDOUS HEAT INDEX VALUES FOR MUCH OF THE GREAT PLAINS AND ALONG THE GULF
COAST. MEANWHILE, OVER THE LAST FEW DAYS MODEL ENSEMBLES HAVE BECOME
INCREASINGLY BULLISH REGARDING THE DEVELOPMENT OF TROUGHING OVER THE WEST
COAST, WHICH IS LIKELY TO BRING A WELCOME MODERATION TO EXTREME HEAT CURRENTLY
IN PLACE OVER THE INTERMOUNTAIN WEST AND MAY HELP TO ENHANCE MOISTURE ADVECTION
INTO THE SOUTHWEST MONSOON REGION. MODEL SOLUTIONS HAVE ALSO BEEN DEPICTING
FAIRLY DEEP TROUGHING OVER HUDSON BAY DURING THE WEEK-2 PERIOD INTERACTING WITH
GULF MOISTURE OVER THE OHIO VALLEY AND PRODUCING POTENTIALLY HEAVY
PRECIPITATION, ALTHOUGH TODAY'S SOLUTIONS SHIFT THIS TROUGH EASTWARD OVER THE
NORTH ATLANTIC BY THE MIDDLE OF THE FORECAST PERIOD.
THE POTENTIAL FOR EXTREME HEAT CONTINUES TO BE SUPPORTED BY A VARIETY OF
FORECAST TOOLS, AND FORECAST CONFIDENCE IS COMPARABLE TO WHAT IT WAS YESTERDAY.
THE GEFS-ECMWF COMBINED EXTREME HEAT TOOL SHOWS WIDESPREAD 40% OR GREATER
CHANCES (AS HIGH AS 70%) FOR PORTIONS OF THE SOUTH-CENTRAL CONUS OF EITHER
MAXIMUM TEMPERATURES OR HEAT INDEX VALUES TO EXCEED THE 90TH PERCENTILE AT SOME
POINT DURING THE WEEK-2 PERIOD FOR MUCH OF THE CONUS EAST OF THE ROCKIES EXCEPT
ALONG THE NORTHERN TIER. WHEN CONSIDERED INDIVIDUALLY THE TWO MODELS DISAGREE
SOMEWHAT WITH RESPECT TO REGIONS AFFECTED AND SIGNAL STRENGTH BUT HAVE GOOD
AGREEMENT WHERE THE SIGNAL IS STRONGEST (SOUTH-CENTRAL AND SOUTHEASTERN
STATES). GIVEN ALL THIS, A MODERATE RISK OF EXTREME HEAT IS POSTED FOR PORTIONS
OF THE SOUTHERN AND CENTRAL PLAINS AND THE LOWER MISSISSIPPI VALLEY COVERING
AUG 13-16. HEAT INDEX VALUES OF 105-110 DEG F ARE GENERALLY DEPICTED BY THE
GEFS AND ECENS MODELS IN THIS REGION. A SLIGHT RISK OF EXTREME HEAT REMAINS
POSTED FOR MUCH OF THE SOUTHEASTERN AND SOUTH-CENTRAL CONUS, VALID FOR ALL OF
WEEK-2.
MODEL ENSEMBLES ARE SHOWING INCREASED SIGNAL OF ENHANCED PRECIPITATION STEMMING
FROM THE SOUTHWESTERN MONSOON. DYNAMICAL MODELS ARE DEPICTING A POTENTIAL
ENHANCEMENT OF MONSOON CONVECTION THROUGH THE MIDDLE OF WEEK-2, WITH
UNCALIBRATED PROBABILITIES FROM THE ECMWF AND GEFS INDICATING WIDESPREAD >50%
CHANCES OF 3-DAY PRECIPITATION TOTALS TO EXCEED HALF AN INCH, WITH SOME
LOCATIONS SEEING 20% CHANCES OF 1 INCH ACCUMULATIONS ALONG WITH HIGHER
PROBABILITIES CENTERED OVER THE CENTRAL ROCKIES. THE TREND IN INCREASED MONSOON
ACTIVITY AMONG MODEL ENSEMBLES HAS BEEN CONTINUING FOR SEVERAL DAYS NOW,
WARRANTING A CONTINUATION OF A MODERATE RISK OF HEAVY PRECIPITATION FOR
PORTIONS OF THE DESERT SOUTHWEST AND SOUTHERN GREAT BASIN VALID AUG 13-15. A
SLIGHT RISK OF HEAVY PRECIPITATION REMAINS VALID FOR THE DESERT SOUTHWEST AND
MUCH OF THE SOUTHERN GREAT BASIN COVERING ALL OF THE WEEK-2 PERIOD. THIS REGION
IS PRONE TO FLASH FLOODING WITH RELATIVELY SMALL PRECIPITATION ACCUMULATIONS
ESPECIALLY ALONG DRY CREEK BEDS (ARROYOS) AND IN CANYONS AND EXTREME CAUTION
SHOULD BE EXERCISED IN SUCH AREAS SHOULD THUNDERSTORM ACTIVITY INITIATE NEARBY.
MONSOONAL THUNDERSTORMS CAN ALSO PRODUCE DRY LIGHTNING, RESULTING IN INCREASED
WILDFIRE RISK.
MULTI-MODEL ENSEMBLE MEANS AGREE THAT A 500-HPA TROUGH SHIFTS EAST NEAR THE
GREAT LAKES AT THE BEGINNING OF WEEK-2, WHICH COULD RESULT IN MESOSCALE
CONVECTIVE SYSTEMS (MCS) TRACKING SOUTHEASTWARD ACROSS THE MIDWEST. GIVEN THE
VERY HUMID AIRMASS, ANY MCS WILL BE CAPABLE OF PRODUCING FLASH FLOODING.
PATTERN RECOGNITION AND 1 TO 3-DAY PRECIPITATION AMOUNTS FROM THE GEFS AND
ECENS WERE USED AS GUIDES TO DEFINE THE SLIGHT RISK OF HEAVY PRECIPITATION,
VALID AUGUST 13-15.
A RAPID ONSET DROUGHT (ROD) RISK IS DESIGNATED FOR PARTS OF THE CENTRAL AND
SOUTHERN PLAINS ALONG WITH THE OZARKS REGION WHERE 30-DAY PRECIPITATION
DEFICITS ARE GREATER THAN 2 INCHES AND CONTINUED DRYNESS AND HEAT ARE FORECAST
THROUGH EARLY TO MID-AUGUST.
FORECASTER: ANTHONY ARTUSA
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