453
FXUS21 KWNC 011831
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 01 2026
SYNOPSIS: MODEL ENSEMBLES FAVOR A CONTINUATION OF EXTREME HEAT ALREADY UNDER
WAY ACROSS MUCH OF THE GREAT PLAINS AND SOUTHERN TIER PERSISTING INTO WEEK-2
TIED TO ANOMALOUS MID-LEVEL HIGH PRESSURE NEAR THE LOWER MISSISSIPPI VALLEY
INCREASING THE CHANCES OF ABOVE-NORMAL TEMPERATURES ACROSS SOUTHERN AND CENTRAL
CONTIGUOUS U.S. (CONUS), WHICH WHEN COMBINED WITH GULF MOISTURE IS LIKELY TO
PRODUCE HIGH HEAT INDICES EAST OF THE ROCKIES. A POTENTIAL SURGE OF MOISTURE
FROM THE GULF OF CALIFORNIA MAY RESULT IN HEAVY PRECIPITATION OVER PORTIONS OF
THE DESERT SOUTHWEST AND GREAT BASIN. ANTECEDENT DRYNESS, COMBINED WITH LITTLE
PRECIPITATION FAVORED OVER THE NEXT TWO WEEKS SUPPORTS A RAPID ONSET DROUGHT
(ROD) RISK FOR PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY AND SOUTHERN AREAS OF THE MIDDLE MISSISSIPPI VALLEY.
HAZARDS
MODERATE RISK OF EXTREME HEAT FOR MUCH OF THE SOUTHERN PLAINS, AND LOWER AND
MIDDLE MISSISSIPPI VALLEY, WED, SEP 9.
SLIGHT RISK OF EXTREME HEAT ACROSS MUCH OF THE GREAT PLAINS, MISSISSIPPI, OHIO,
AND TENNESSEE VALLEYS, AND SOUTHEAST U.S., WED-SAT, SEP 9-12.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE DESERT SOUTHWEST AND
GREAT BASIN, WED-FRI, SEP 9-11.
RAPID ONSET DROUGHT (ROD) RISK FOR PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS
AND THE MIDDLE AND LOWER MISSISSIPPI VALLEY.
DETAILED SUMMARY
FOR FRIDAY SEPTEMBER 04 - TUESDAY SEPTEMBER 08:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY SEPTEMBER 09 - TUESDAY SEPTEMBER 15: DYNAMICAL MODEL GUIDANCE
REMAINS IN GOOD AGREEMENT REGARDING SUBTROPICAL RIDGING PERSISTING OVER THE
SOUTH-CENTRAL U.S. INTO EARLY WEEK-2, WITH THE 0Z ECMWF, GEFS, AND CANADIAN
ENSEMBLES DEPICTING A 594 DM 500-HPA HEIGHT MAXIMUM AT THE START OF THE
FORECAST PERIOD OVER THE LOWER MISSISSIPPI VALLEY. MODELS QUICKLY BREAK DOWN
THIS RIDGE AND THEN DIVERGE QUITE A BIT, POTENTIALLY INDICATING AN IMPENDING
SYNOPTIC REORGANIZATION. THIS, COUPLED WITH THE DECREASING SOLAR ANGLES AND
INSOLATION POINTS TO SOME RELIEF FROM THE LONG-LASTING HEAT WAVE THAT HAS BEEN
AFFECTING THE SOUTHERN CONUS.
DESPITE THESE INDICATIONS THE POTENTIAL FOR EXTREME HEAT REMAINS FOR MUCH OF
THE GREAT PLAINS, MISSISSIPPI AND OHIO VALLEYS, AND SOUTHEAST U.S. THROUGH
ABOUT THE MIDDLE OF THE FORECAST PERIOD. THE GREATEST POTENTIAL IS ON DAY-8
(SEP 9), WHERE ENSEMBLE CALCULATED HEAT INDICES ABOVE 105F REMAIN WIDESPREAD
ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY, AND ABOVE 95F AS FAR
NORTH AS CENTRAL ILLINOIS. HEAT INDICES ABOVE 100F ARE ALSO FAVORED ACROSS THE
SOUTHEAST U.S. BY DAY-11 (SEP 12) THE HEAT SIGNAL IS LOWER, WITH INDICATED HEAT
INDICES ABOUT 5F LOWER THAN AT THE OUTSET OF WEEK-2. THE DECREASE IN HEAT RISK
IS REFLECTED IN THE PROBABILISTIC EXTREMES TOOLS AS WELL, WITH BOTH THE GEFS
AND ECWMF INITIALLY INDICATING A 40% CHANCE OF MAXIMUM TEMPERATURES TO EXCEED
THE 90TH PERCENTILE, BEFORE DROPPING TO BELOW A 20% CHANCE BY THE END OF THE
FORECAST PERIOD. A MODERATE RISK OF EXTREME HEAT REMAINS POSTED FOR MUCH OF THE
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY FOR SEP 9, AND A SLIGHT RISK OF
EXTREME HEAT FOR MUCH OF THE GREAT PLAINS, MISSISSIPPI AND OHIO VALLEYS, AND
SOUTHEASTERN CONUS, VALID SEP 9-12.
MODEL ENSEMBLES INDICATE A FAIRLY STRONG MID-LEVEL TROUGH OVER THE WEST COAST
EARLY IN WEEK-2. THIS MAY COMBINE WITH ENHANCED MOISTURE FROM THE GULF OF
CALIFORNIA DUE TO ACTIVE TROPICAL CYCLONES OVER THE EASTERN PACIFIC TO GENERATE
HEAVY PRECIPITATION OVER THE NORTH AMERICAN MONSOON REGION. UNCALIBRATED
PROBABILITIES FROM THE GEFS AND ECMWF BOTH INDICATE AT LEAST A 20% CHANCE OF
3-DAY PRECIPITATION TO EXCEED HALF AN INCH OVER THE REGION EARLY IN THE
FORECAST PERIOD. THE ECMWF IS MORE BULLISH, BOTH IN TERMS OF RAINFALL TOTALS
AND DURATION OF THE EVENT, BUT GIVEN THE LACK OF SUPPORT FROM THE GEFS A SLIGHT
RISK OF HEAVY PRECIPITATION IS POSTED OVER PORTIONS OF THE DESERT SOUTHWEST AND
GREAT BASIN FOR DAYS 8-10 ONLY (SEP 9-11). THIS REGION IS PRONE TO FLASH
FLOODING AND CAUTION SHOULD BE EXERCISED NEAR CANYONS AND CREEK BEDS, AND
ADDITIONAL RAINFALL MAY HAMPER RECOVERY EFFORTS FROM RECENT FLOODING IN THE
GRAND CANYON.
A RAPID ONSET DROUGHT (ROD) RISK REMAINS DESIGNATED FOR MUCH OF THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY AND ADJACENT PORTIONS OF THE CENTRAL
PLAINS, TENNESSEE AND MIDDLE MISSISSIPPI VALLEYS, AND SOUTHEAST U.S. THIS ROD
AREA CONTINUES TO REGISTER 30-DAY PRECIPITATION DEFICITS GREATER THAN 2 INCHES,
WITH LITTLE RAINFALL FORECAST DURING THE NEXT TWO WEEKS. MUCH OF THIS ROD AREA
IS ALSO INCLUDED WITHIN THE MODERATE RISK OF EXTREME HEAT AS THE POTENTIAL FOR
INCREASED EVAPOTRANSPIRATION RATES ALSO LOOKS TO REINFORCE THIS RISK INTO
SEPTEMBER.
FORECASTER: DANNY BARANDIARAN
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