460
FXUS21 KWNC 251815
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 25 2023
SYNOPSIS: THIS PAST SUMMER HAS BEEN RELENTLESS IN TERMS OF HEAT OVER THE
CENTRAL AND SOUTHERN PORTIONS OF THE CONTIGUOUS U.S. AND IT IS NOT PREDICTED TO
ABATE GOING INTO SEPTEMBER. FOLLOWING A BRIEF RESPITE TOWARD THE END OF WEEK-1,
ALL INDICATIONS ARE FOR HEAT TO AGAIN INCREASE ACROSS MUCH OF THE GREAT PLAINS
AND MISSISSIPPI VALLEY AROUND LABOR DAY WEEKEND. ABOVE-NORMAL TEMPERATURES ARE
FORECAST TO SPREAD NORTHWARD AND EASTWARD THROUGH WEEK-2, ACROSS PARTS OF THE
MIDWEST AND TENNESSEE VALLEY, ALTHOUGH THERE IS LESS CONFIDENCE REGARDING
REACHING EXCESSIVE HEAT CRITERIA IN THOSE AREAS DUE TO GENERALLY LOWER HUMIDITY
VALUES FORECAST.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY, SAT-SUN, SEP 2-3.
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, MIDDLE AND LOWER MISSISSIPPI VALLEY, AND SOUTHEAST, SAT-TUE, SEP 2-5.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF NEW MEXICO, THE GREAT PLAINS, THE
MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, AND THE SOUTHEAST, SAT-FRI, SEP 2-8.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR MONDAY AUGUST 28 - FRIDAY SEPTEMBER 01:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY SEPTEMBER 02 - FRIDAY SEPTEMBER 08: ELEVATED CHANCES FOR EXCESSIVE
HEAT ARE FORECAST TO CONTINUE ACROSS PORTIONS OF THE CENTRAL AND EAST-CENTRAL
CONUS DURING WEEK-2 AS MID-LEVEL HEIGHTS INCREASE. THE HIGHEST CONFIDENCE FOR
EXCESSIVE HEAT IS ACROSS PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY, WHERE A HIGH RISK OF EXCESSIVE HEAT IS POSTED FOR SEP 2-3. MAXIMUM
TEMPERATURES CONTINUE TO TREND UPWARD IN THE MODEL GUIDANCE, WITH THE ECMWF
PROBABILISTIC EXTREMES TOOL (PET) DEPICTING AT LEAST A 60 PERCENT CHANCE
TEMPERATURES EXCEED THE 90TH CLIMATOLOGICAL PERCENTILE AND 100 DEG F OVER PARTS
OF THE REGION ON DAY-9 (SEP 3). ADDITIONALLY, THE 0Z DETERMINISTIC ECMWF HAS
SOME ISOLATED AREAS EXCEEDING 105 DEG F AND THE NATIONAL BLEND OF MODELS
INDICATES INCREASED POTENTIAL FOR DAILY RECORD HIGH TEMPERATURES ACROSS PARTS
OF TEXAS FURTHER SUPPORTING THE UPGRADE TO A HIGH RISK. HUMIDITY VALUES ARE
FORECAST TO BE LOWER COMPARED TO EARLIER IN THE SUMMER, ALTHOUGH SOME AREAS
COULD HAVE HEAT INDICES EXCEED 105 DEG F BASED ON THE ECMWF HEAT GUIDANCE (110
DEG F CLOSER TO THE GULF OF MEXICO COAST).
A MODERATE RISK OF EXCESSIVE HEAT IS POSTED FOR SEP 2-5, AND IS EXTENDED
THROUGH PARTS OF THE CENTRAL PLAINS, MIDDLE MISSISSIPPI VALLEY, AND SOUTHEAST
WHERE TEMPERATURES WELL INTO THE 90S DEG F ARE POSSIBLE WITH HEAT INDICES
EXCEEDING 100 DEG F IN SOME AREAS (105 DEG F OVER PARTS OF THE SOUTHEAST). THE
HEAT IS FORECAST TO CONTINUE SPREADING NORTH AND EAST THROUGHOUT WEEK-2,
ALTHOUGH LOWER HUMIDITY VALUES MAY PREVENT MANY NORTHERN AREAS FROM REACHING
EXCESSIVE HEAT CRITERIA. THE SLIGHT RISK OF EXCESSIVE HEAT IS VALID FOR ALL OF
WEEK-2 AND INCLUDES PARTS OF THE MIDWEST AND THE TENNESSEE AND OHIO VALLEYS
WHERE TEMPERATURES MAY REACH OR EXCEED 90 DEG F BASED ON THE ECMWF PET AND
UNCALIBRATED TEMPERATURES FROM THE 0Z ECMWF ENSEMBLE MEAN. HEAT INDEX VALUES
ARE MORE UNCERTAIN GIVEN THE RELATIVELY DRIER AIR BUT COULD HAVE ELEVATED
POTENTIAL FOR HEAT INDICES APPROACHING 100 DEG F OVER SOME OF THE HIGHLIGHTED
AREAS. THE GEFS CONTINUES TO BE MORE ROBUST WITH TEMPERATURES ACROSS THE
CENTRAL CONUS, ALTHOUGH CAUTION IS GIVEN DUE TO ITS WARM BIAS. HOWEVER, GIVEN
THE UPWARD TREND IN TEMPERATURES IN THE ECMWF AND CANADIAN ENSEMBLES COMBINED
WITH WHAT HAS ALREADY BEEN A HOT SUMMER, THE HEAT RISK LEVELS WERE ADJUSTED
UPWARD ACCORDINGLY.
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.
IN THE TROPICS, THE ATLANTIC MAIN DEVELOPMENT REGION IS FORECAST TO BECOME MORE
ACTIVE IN THE WEEKS 2-3 TIMEFRAME, COINCIDING WITH THE PEAK OF HURRICANE
SEASON. THE LATEST GLOBAL TROPICS HAZARDS OUTLOOK INDICATES 60 AND 40 PERCENT
CHANCES FOR TROPICAL CYCLONE DEVELOPMENT IN WEEKS 2 AND 3 RESPECTIVELY. AT THIS
TIME SCALE, IT IS TOO EARLY TO DETERMINE ANY POTENTIAL U.S. IMPACTS, AND
INTERESTS ARE ADVISED TO REFER TO THE NATIONAL HURRICANE CENTER FOR THE LATEST
UPDATES AND TRACK GUIDANCE.
MID-LEVEL RIDGING IS FORECAST TO BUILD TO THE SOUTH OF ALASKA FAVORING A DRIER
PATTERN ACROSS PARTS OF THE SOUTHEASTERN MAINLAND AND SOUTHEAST ALASKA COMPARED
TO WEEK-1. TROUGHING OVER THE BERING SEA CONTINUES TO FAVOR SOUTHWESTERLY
MID-LEVEL FLOW ACROSS MUCH OF THE MAINLAND, WITH ENHANCED CHANCES FOR
ABOVE-NORMAL PRECIPITATION. HOWEVER, TOTALS ARE NOT EXPECTED TO REACH HAZARDOUS
THRESHOLDS. TEMPERATURES ARE GENERALLY FORECAST TO LEAN NEAR- TO ABOVE-NORMAL
ACROSS MOST OF THE STATE.
FORECASTER: THOMAS COLLOW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page