973
FXUS21 KWNC 221819
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 22 2023
SYNOPSIS: DURING WEEK-2, MID-LEVEL HIGH PRESSURE IS FORECAST ACROSS MUCH OF THE
INTERIOR WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS) RESULTING IN ABOVE-NORMAL
TEMPERATURES PERSISTING ACROSS MANY OF THESE AREAS. DOWNSTREAM, MID-LEVEL LOW
PRESSURE IS FAVORED TO AMPLIFY ACROSS THE EAST. THIS FAVORS DIMINISHING HEAT
CONCERNS ACROSS THE SOUTHEAST, AS WELL AS A DEVELOPMENT OF A FRONTAL BOUNDARY
AND INCREASED CHANCES FOR HEAVY RAINFALL. AN INCREASING POTENTIAL FOR TROPICAL
ACTIVITY IS ALSO A CONCERN, WITH SEVERAL RECENT DETERMINISTIC AND ENSEMBLE
MODEL SOLUTIONS DEPICTING A TROPICAL CYCLONE DEVELOPING IN THE GULF OF MEXICO
EARLY IN WEEK-2. WHILE EXCESSIVE HEAT AND ABNORMALLY DRY CONDITIONS CONTINUE TO
FAVOR AN ENHANCED RAPID ONSET DROUGHT RISK ACROSS PARTS OF THE SOUTHERN PLAINS
AND LOWER MISSISSIPPI VALLEY, ANY TROPICAL SYSTEM AND ASSOCIATED HEAVY RAINFALL
COULD REDUCE THIS RISK ACROSS THE LOWER MISSISSIPPI VALLEY DEPENDING ON THE
TRACK.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF EASTERN TEXAS AND WESTERN
LOUISIANA, WED-SAT, AUG 30-SEP 2.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF NEW MEXICO, THE CENTRAL AND
SOUTHERN PLAINS, AND THE LOWER MISSISSIPPI VALLEY, WED-TUE, AUG 30-SEP 5.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE NORTHERN PLAINS, WED, AUG 30.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL GULF OF MEXICO
COAST AND SOUTHEAST, WED-FRI, AUG 30-SEP 1.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR FRIDAY AUGUST 25 - TUESDAY AUGUST 29:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY AUGUST 30 - TUESDAY SEPTEMBER 05: ELEVATED CHANCES FOR EXCESSIVE
HEAT ARE FORECAST TO CONTINUE ACROSS PORTIONS OF THE GREAT PLAINS AND LOWER
MISSISSIPPI VALLEY DURING WEEK-2 DUE TO INCREASED RIDGING, ALTHOUGH THE 500-HPA
HEIGHT ANOMALIES ARE PREDICTED TO BE MUCH MORE MUTED COMPARED TO NOW. THE ECMWF
PROBABILISTIC EXTREMES TOOL (PET) DEPICTS AREAS WITH AT LEAST A 20 PERCENT
CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE 85H CLIMATOLOGICAL PERCENTILE AND
95 DEG F ACROSS PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY,
AS WELL AS OVER THE NORTHERN PLAINS EARLY IN THE PERIOD, POSSIBLY DUE IN PART
TO INCREASED DOWNSLOPE FLOW. BY THE MIDDLE OF WEEK-2, THESE ELEVATED
PROBABILITIES CONSOLIDATE ACROSS THE CENTRAL AND SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY, WITH THE HIGHEST PROBABILITIES (GREATER THAN 40 PERCENT)
PERSISTING ACROSS EASTERN TEXAS. THE GEFS IS MORE AGGRESSIVE WITH THE HEAT
ACROSS THE GREAT PLAINS AND MISSISSIPPI VALLEY, BUT GIVEN ITS KNOWN WARM BIAS,
AS WELL AS THE CANADIAN ENSEMBLE BEING MORE IN LINE WITH THE RELATIVELY COOLER
ECMWF, THE ECMWF PET GUIDANCE IS PREFERRED OVER THE GEFS IN TODAY’S FORECAST.
A SLIGHT RISK FOR EXCESSIVE HEAT IS POSTED ACROSS PORTIONS OF NEW MEXICO, THE
CENTRAL AND SOUTHERN PLAINS, AND THE LOWER MISSISSIPPI VALLEY FOR ALL OF WEEK-2
WHERE TEMPERATURES EXCEEDING 95 DEG F ARE MOST LIKELY, WITH POTENTIAL FOR HEAT
INDICES TO EXCEED 105 DEG F. A SECOND SLIGHT RISK OF EXCESSIVE HEAT IS
HIGHLIGHTED ACROSS THE NORTHERN PLAINS WHERE TEMPERATURES WELL INTO THE 90S DEG
F ARE POSSIBLE ON DAY-8 (AUG 30). THEREAFTER, HEAT IS MORE LIKELY TO SHIFT
SOUTHWARD ACROSS THE PLAINS. A MODERATE RISK FOR EXCESSIVE HEAT CONTINUES
ACROSS PORTIONS OF EASTERN TEXAS AND WESTERN LOUISIANA FOR AUG 30-SEP 2 GIVEN
THE HIGHER PROBABILITIES IN THE ECMWF PET, WITH THE UNCALIBRATED ECMWF
ENSEMBLES ALSO DEPICTING TEMPERATURES NEAR OR EXCEEDING 100 DEG F IN SOME AREAS
AND HEAT INDICES OVER 110 DEG F. DUE TO INCREASING PRECIPITATION CHANCES AND
UNCERTAINTY IN THE TROPICS, THE EXCESSIVE HEAT RISKS ARE DISCONTINUED ACROSS
THE EASTERN GULF OF MEXICO COAST AND FLORIDA.
TROUGHING IN THE EAST FAVORS THE FORMATION OF A FRONTAL BOUNDARY ACROSS THE
SOUTHEAST BECOMING A FOCAL POINT FOR INCREASED PRECIPITATION CHANCES. THE ECMWF
PET DEPICTS PORTIONS OF THE CENTRAL GULF COAST AND SOUTHEAST COAST HAVING AT
LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE 85TH
CLIMATOLOGICAL PERCENTILE AND 1-INCH EARLY IN THE PERIOD. THE UNCALIBRATED
ECMWF ENSEMBLE IS EVEN MORE ROBUST, DEPICTING SOME AREAS WITH AT LEAST A 20
PERCENT CHANCE OF 3-DAY PRECIPITATION EXCEEDING 2-INCHES. THE GEFS PET CONFINES
THESE ENHANCED PROBABILITIES TO THE EASTERN GULF OF MEXICO COAST. WHILE THE
FRONTAL BOUNDARY ALONE FAVORS INCREASED PRECIPITATION, SEVERAL MODEL ENSEMBLES,
PARTICULARLY THE ECMWF, ARE SHOWING THE POTENTIAL FOR A TROPICAL SYSTEM TO
DEVELOP OVER THE GULF OF MEXICO EARLY IN WEEK-2. WHILE THE TRACK IS VERY
UNCERTAIN, ANY TROPICAL SYSTEM COULD FURTHER EXACERBATE PRECIPITATION.
TROPICAL STORM FRANKLIN, CURRENTLY LOCATED TO THE SOUTH OF HISPANIOLA, IS
FORECAST TO STRENGTHEN INTO A HURRICANE AS IT MOVES INTO THE WESTERN ATLANTIC.
LATE IN WEEK-1 INTO THE OUTSET OF WEEK-2, FRANKLIN IS FORECAST TO MAKE ITS
CLOSEST APPROACH TO THE NORTHEASTERN CONUS. WHILE THE STORM IS PROJECTED TO
REMAIN FAR ENOUGH OFFSHORE MINIMIZING THE LIKELIHOOD OF DIRECT IMPACTS,
INCREASED SURF AND ELEVATED RIP CURRENT RISK ARE POSSIBLE ACROSS COASTAL AREAS
OF THE NORTHEAST. 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.
WHILE MOST GUIDANCE FAVORS HIGHEST WEEK-2 PRECIPITATION TOTALS ACROSS THE
SOUTHEAST, ANY WESTWARD DEVIATION COULD RESULT IN DECREASING ROD RISK ACROSS
THE LOWER MISSISSIPPI VALLEY.
OVER ALASKA, NO HAZARDS ARE POSTED. MID-LEVEL TROUGHING FAVORED OVER THE BERING
SEA AND THE WESTERN MAINLAND IS EXPECTED TO BRING PRECIPITATION TO
SOUTH-CENTRAL AND SOUTHEASTERN PORTIONS OF THE MAINLAND, THOUGH TOTALS ARE NOT
EXPECTED TO REACH HAZARDOUS THRESHOLDS.
FORECASTER: THOMAS COLLOW
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