240
FXUS21 KWNC 241817
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 24 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 AND HUMIDITY TO AGAIN INCREASE ACROSS THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY. WEAKENING MID-LEVEL LOW PRESSURE IN THE
EAST ALSO FAVORS ABOVE-NORMAL TEMPERATURES EXPANDING NORTHWARD AND EASTWARD,
ACROSS PARTS OF THE MIDWEST AND TENNESSEE VALLEY, ALTHOUGH THERE IS LESS
CONFIDENCE REGARDING REACHING EXCESSIVE HEAT CRITERIA IN THOSE AREAS. WHILE
LINGERING PRECIPITATION IS POSSIBLE ACROSS THE FLORIDA PENINSULA AT THE OUTSET
OF THE PERIOD, IMPACTS FROM A POTENTIAL TROPICAL DISTURBANCE ARE MORE LIKELY TO
OCCUR IN THE WEEK-1 PERIOD, ALLOWING THE PRECIPITATION HAZARD TO BE
DISCONTINUED IN THE SOUTHEAST.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST, FRI-MON, SEP 1-4.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF NEW MEXICO, THE CENTRAL AND
SOUTHERN PLAINS, THE MIDDLE AND LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND
THE SOUTHEAST, FRI-THU, SEP 1-7.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR SUNDAY AUGUST 27 - THURSDAY AUGUST 31:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY SEPTEMBER 01 - THURSDAY SEPTEMBER 07: ELEVATED CHANCES FOR EXCESSIVE
HEAT ARE FORECAST TO CONTINUE ACROSS PORTIONS OF THE SOUTH-CENTRAL AND
SOUTHEASTERN CONUS DURING WEEK-2 AS MID-LEVEL HEIGHTS INCREASE IN THE WAKE OF A
DEPARTING TROUGH IN THE EAST. THE HIGHEST CONFIDENCE FOR EXCESSIVE HEAT IS
ACROSS PORTIONS OF THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND
SOUTHEAST, WHERE A MODERATE RISK OF EXCESSIVE HEAT IS POSTED FOR SEP 1-4. IN
THESE AREAS TEMPERATURES ARE LIKELY TO BE IN THE MID- TO UPPER-90S DEG F, WITH
SOME PARTS OF TEXAS POSSIBLY EXCEEDING 100 DEG F. THE CALIBRATED HEAT TOOL FROM
THE ECMWF ALSO DEPICTS A 30-50 PERCENT CHANCE HEAT INDICES EXCEED THE 90TH
CLIMATOLOGICAL PERCENTILE ACROSS PARTS OF TEXAS AND THE LOWER MISSISSIPPI
VALLEY, WITH SOME AREAS POTENTIALLY HAVING HEAT INDICES GREATER THAN 110 DEG F.
WHILE THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) INDICATES 60 PERCENT OF
GREATER PROBABILITIES FOR MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE
AND 100 DEG F ACROSS PARTS OF NORTH TEXAS ON DAY-9 (9/2), WHICH WOULD SUPPORT A
HIGH RISK, A MODERATE RISK IS PREFERRED GIVEN THAT EVEN THOUGH SOME TRIPLE
DIGIT HEAT IS LIKELY OVER PARTS OF THE REGION, TEMPERATURES ARE NOT EXPECTED TO
BE AS HIGH AS DURING WEEK-1 AND DUE TO LITTLE SIGNAL FOR RECORD TEMPERATURES IN
THE NATIONAL BLEND OF MODELS.
BOTH THE 0Z GEFS AND ECMWF ENSEMBLES INDICATE A TREND TOWARD WARMER
TEMPERATURES ACROSS MUCH OF THE EASTERN CONUS DURING WEEK-2, ALTHOUGH WHETHER
OR NOT AREAS REACH EXCESSIVE HEAT CRITERIA IS MORE UNCERTAIN GIVEN THE TIME OF
YEAR. HOWEVER, THE ECMWF PET DEPICTS COVERAGE OF AT LEAST A 20 PERCENT CHANCE
MAXIMUM TEMPERATURES REACH THE 85TH CLIMATOLOGICAL PERCENTILE AND 90 DEG F
EXPANDING ACROSS MUCH OF THE LOWER MIDWEST AND TENNESSEE VALLEY BY THE MIDDLE
OF THE PERIOD. THEREFORE, THE SLIGHT RISK OF EXCESSIVE HEAT IS EXPANDED
COMPARED TO YESTERDAY AND INCLUDES PARTS OF NEW MEXICO, THE CENTRAL AND
SOUTHERN PLAINS, MIDDLE AND LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND THE
SOUTHEAST, AND IS VALID FOR ALL OF WEEK-2. THE GEFS IS MUCH MORE ROBUST IN
TERMS OF THE NORTHWARD AND EASTWARD EXPANSION OF THE HEAT, ALTHOUGH CAUTION IS
GIVEN DUE TO ITS WARM BIAS. HUMIDITY IS FORECAST TO BE ON THE LOWER SIDE WHICH
MAY HELP KEEP HEAT INDICES BELOW 100 DEG F. HOWEVER, GIVEN THE UPWARD TREND IN
TEMPERATURES FORECAST DURING EARLY SEPTEMBER COMBINED WITH WHAT HAS ALREADY
BEEN A HOT SUMMER, A SLIGHT RISK IS HIGHLIGHTED.
THE NATIONAL HURRICANE CENTER INDICATES A 60 PERCENT CHANCE OF TROPICAL CYCLONE
FORMATION OVER THE EASTERN GULF OF MEXICO DURING THE NEXT 7-DAYS. HOWEVER, ANY
POTENTIAL RELATED IMPACTS TO FLORIDA OR THE SOUTHEAST ARE FORECAST TO OCCUR
PRIOR TO THE START OF WEEK-2 ALLOWING FOR THE HEAVY PRECIPITATION HAZARD TO BE
DISCONTINUED. ELSEWHERE 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.
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. A
SLIGHT NORTHWARD AND EASTWARD EXPANSION IS MADE COMPARED TO YESTERDAY GIVEN
TODAY’S UPDATE TO THE U.S. DROUGHT MONITOR AND LIKELY EXPANSION OF EXCESSIVE
HEAT INTO WEEK-2.
TROUGHING ALONG THE WEST COAST OF THE CONUS FAVORS INCREASING SOUTHERLY FLOW
AND MOISTURE ADVECTION ACROSS THE FOUR CORNERS AND SOUTHWEST. ADDITIONALLY, THE
NATIONAL HURRICANE CENTER IS MONITORING A DISTURBANCE THAT IS FORECAST TO TRACK
NEAR THE WEST COAST OF MEXICO DURING THE NEXT 7-DAYS WITH A 70 PERCENT CHANCE
OF TROPICAL CYCLONE DEVELOPMENT. THIS COULD FURTHER ENHANCE A GULF SURGE EVENT
LATE IN WEEK-1 INTO EARLY WEEK-2 DEPENDING ON THE EVENTUAL TRACK OF THE SYSTEM.
GIVEN THAT WIDESPREAD IMPACTS ARE NOT ANTICIPATED, NO RELATED FLOODING HAZARD
IS POSTED. HOWEVER ISOLATED AREAS OF HEAVY RAINFALL AND SUBSEQUENT FLASH
FLOODING OR MUDSLIDES ARE POSSIBLE OVER SOME AREAS WHICH ALREADY RECEIVED
COPIOUS AMOUNTS OF RAINFALL DUE TO HILARY.
MID-LEVEL TROUGHING FAVORED OVER THE BERING SEA AND WESTERN MAINLAND ALASKA IS
EXPECTED TO BRING PRECIPITATION TO PORTIONS OF THE SOUTH-CENTRAL AND
SOUTHEASTERN MAINLAND OF ALASKA AROUND THE END OF WEEK-1 INTO THE START OF
WEEK-2. HOWEVER, TOTALS ARE NOT EXPECTED TO REACH HAZARDOUS THRESHOLDS AND A
DRYING TREND IS LIKELY TOWARD THE MIDDLE AND LATER PORTION OF WEEK-2 AS THE
AFOREMENTIONED TROUGHING WEAKENS AND RIDGING BUILDS ACROSS THE STATE.
FORECASTER: THOMAS COLLOW
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