620
FXUS21 KWNC 231831
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 23 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 OVER THE EAST AT THE OUTSET OF THE PERIOD. THIS FAVORS
DIMINISHING HEAT CONCERNS ACROSS THE SOUTHEAST, AS WELL AS A DEVELOPMENT OF A
FRONTAL BOUNDARY AND INCREASED CHANCES FOR HEAVY RAINFALL, ALTHOUGH SIGNALS ARE
WEAKER COMPARED TO YESTERDAY. SOME ENSEMBLE MEMBERS CONTINUE TO DEPICT A
TROPICAL CYCLONE OVER THE GULF OF MEXICO LATE IN THE WEEK-1 PERIOD, WHICH COULD
ALSO INCREASE THE PRECIPITATION POTENTIAL ACROSS THE SOUTHEAST EARLY IN WEEK-2
DEPENDING ON TRACK.
HAZARDS
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY, FRI-SUN, SEP 1-3.
SLIGHT RISK OF EXCESSIVE HEAT FOR PORTIONS OF NEW MEXICO, THE CENTRAL AND
SOUTHERN PLAINS, AND THE LOWER MISSISSIPPI VALLEY, THU-WED, AUG 31-SEP 6.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL GULF OF MEXICO
COAST AND SOUTHEAST, THU-FRI, AUG 31-SEP 1.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR SATURDAY AUGUST 26 - WEDNESDAY AUGUST 30:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY AUGUST 31 - WEDNESDAY SEPTEMBER 06: 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. FOLLOWING
A BRIEF DROP IN HUMIDITY LEVELS IN THE LATE WEEK-1 AND EARLY WEEK-2 TIMEFRAME
ASSOCIATED WITH INCREASED NORTHERLY FLOW AND A RELATIVELY DRIER AIR MASS, HEAT
AND HUMIDITY ARE PREDICTED TO INCREASE ACROSS THE SOUTHERN TIER BY THE MIDDLE
OF WEEK-2, POSSIBLY EXPANDING INTO PARTS OF THE MIDWEST AND TENNESSEE VALLEY AS
WELL. 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. WHILE A SLIGHT REPRIEVE IS POSSIBLE ON
DAY-8 (AUG 31) DUE TO A DECREASE IN HUMIDITY, THIS LOOKS TO BE SHORT-LIVED AND
A MODERATE RISK FOR EXCESSIVE HEAT IS HIGHLIGHTED ACROSS PORTIONS OF THE
SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY FOR SEP 1-3, WHERE THE
UNCALIBRATED ECMWF ENSEMBLES DEPICT TEMPERATURES NEAR OR EXCEEDING 100 DEG F
AND HEAT INDICES OVER 110 DEG F. THE ECMWF PROBABILISTIC EXTREMES TOOL (PET)
ALSO SHOWS GREATER COVERAGE OF 40 PERCENT OR GREATER PROBABILITIES FOR MAXIMUM
TEMPERATURES REACHING THE 85TH PERCENTILE AND 100 DEG F COMPARED TO YESTERDAY
ACROSS PORTIONS OF TEXAS AND SOUTHERN OKLAHOMA BEGINNING ON DAY-9 (SEP 1), AND
THE NATIONAL BLEND OF MODELS ALSO INDICATES ELEVATED POTENTIAL FOR DAILY RECORD
HIGH TEMPERATURES ON DAYS 9 AND 10 (SEP 1-2).
THE GEFS IS MUCH MORE ROBUST IN TERMS OF THE NORTHWARD AND EASTWARD EXPANSION
OF THE HEAT THROUGH THE NORTHERN AND CENTRAL PLAINS AND MIDWEST, BUT GIVEN ITS
KNOWN WARM BIAS, THE COMPARATIVELY COOLER ECMWF SOLUTION REMAINS PREFERRED.
HOWEVER, EVEN THE UNCALIBRATED 0Z ECMWF ENSEMBLE DEPICTS AN EXPANSIVE AREA OF
TEMPERATURES EXCEEDING 90 DEG F BUILDING INTO PARTS OF THE MIDWEST AND
TENNESSEE VALLEY BY THE MIDDLE OF THE PERIOD. GIVEN THE EXPECTATION OF LOW
HUMIDITY VALUES, NO EXPANSION OF THE SLIGHT RISK OF EXCESSIVE HEAT IS MADE IN
TODAY’S FORECAST, BUT TRENDS WILL CONTINUE TO BE MONITORED.
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 AT LEAST A 20 PERCENT CHANCE OF 3-DAY PRECIPITATION EXCEEDING THE
85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH EARLY IN THE PERIOD OVER MUCH OF THE
FLORIDA PENINSULA, WITH THE GEFS PET NO LONGER DEPICTING THESE ENHANCED
PROBABILITIES. HOWEVER, TROPICAL CYCLONE FORMATION REMAINS A POSSIBILITY OVER
THE GULF OF MEXICO DURING WEEK-1, AS INDICATED BY MANY 0Z ECMWF ENSEMBLE
MEMBERS, WHICH COULD FURTHER ENHANCE MOISTURE ACROSS THE SOUTHEAST AND FLORIDA
EARLY IN WEEK-2. THEREFORE, A SLIGHT RISK OF HEAVY PRECIPITATION REMAINS POSTED
ACROSS PORTIONS OF THE SOUTHEAST FOR DAYS 8 AND 9 (AUG 31-SEP 1). 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.
WHILE MOST GUIDANCE FAVORS THE HIGHEST WEEK-2 PRECIPITATION TOTALS ACROSS THE
SOUTHEAST, ANY WESTWARD DEVIATION COULD RESULT IN DECREASING ROD RISK ACROSS
THE LOWER MISSISSIPPI VALLEY.
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 80 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.
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. 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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