058
FXUS21 KWNC 041845
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 04 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 ADJACENT AREAS.
HAZARDS
MODERATE RISK OF EXTREME HEAT FOR PORTIONS OF THE SOUTHERN AND CENTRAL PLAINS,
AND THE LOWER MISSISSIPPI VALLEY, WED-SAT, AUG 12-15.
SLIGHT RISK OF EXTREME HEAT FOR MUCH OF THE SOUTH-CENTRAL CONUS, SOUTHEAST
U.S., AND MID-ATLANTIC, WED-TUE, AUG 12-18.
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST AND
SOUTHERN GREAT BASIN, WED-FRI, AUG 12-14.
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF THE DESERT SOUTHWEST AS WELL AS
PORTIONS OF THE SOUTHERN GREAT BASIN AND THE SOUTHERN AND CENTRAL ROCKIES,
WED-TUE, AUG 12-18.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE GREAT LAKES AND THE OHIO
AND UPPER MISSISSIPPI VALLEYS, WED-FRI, AUG 12-14.
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 FRIDAY AUGUST 07 - TUESDAY AUGUST 11:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY AUGUST 12 - TUESDAY AUGUST 18: MULTIPLE MODEL ENSEMBLES DEPICT
ANOMALOUS MID-LEVEL RIDGING PERSISTING OVER THE SOUTHEASTERN CONUS THROUGHOUT
WEEK-2, WITH A CLOSED 594-DM 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 DEWPOINTS 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 HIGHER TODAY GIVEN AN INCREASED
SIGNAL STRENGTH RELATIVE TO THE PAST FEW DAYS. THE GEFS-ECWMF COMBINED EXTREME
HEAT TOOL SHOWS WIDESPREAD 40% OR GREATER CHANCES (AS HIGH AS 70% FOR PORTIONS
OF THE LOWER MISSISSIPPI VALLEY) OF EITHER MAXIMUM TEMPERATURES OR HEAT INDEX
VALUES TO EXCEED THE 90TH PERCENTILE AT SOME POINT DURING THE WEEK-2 PERIOD FOR
MOST OF THE CONUS EAST OF THE ROCKIES EXCEPT ALONG THE NORTHERN TIER.
ADDITIONALLY, PROBABILITIES EXCEED 40% AND AS HIGH AS 60% FOR THE SAME
THRESHOLD ACROSS EAST TEXAS AND THE LOWER MISSISSIPPI VALLEY. 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.
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
12-15. A SLIGHT RISK OF EXTREME HEAT REMAINS POSTED FOR MUCH OF THE
SOUTHEASTERN AND SOUTH-CENTRAL CONUS, VALID FOR ALL OF WEEK-2. GIVEN THE
INCREASING CONFIDENCE IN TROUGHING OVER THE WEST COAST AND ITS MODERATING
INFLUENCE, THE SLIGHT RISK OF EXTREME HEAT FOR THE INTERMOUNTAIN WEST AND
NORTHERN PLAINS HAS BEEN DISCONTINUED IN TODAY’S OUTLOOK.
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 ECWMF 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 12-14. A
SLIGHT RISK OF HEAVY PRECIPITATION REMAINS VALID FOR MUCH OF THE DESERT
SOUTHWEST AND 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 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 12-14.
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: DANNY BARANDIARAN
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