601
FXUS21 KWNC 161759
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 16 2023
SYNOPSIS: THE WEEK-2 PERIOD IS PREDICTED TO BE DOMINATED BY MID-LEVEL HIGH
PRESSURE ACROSS MUCH OF THE CONTIGUOUS U.S. (CONUS) GRADUALLY WEAKENING WITH
TIME, EXCLUDING THE NORTHEASTERN QUADRANT. THIS PATTERN SUPPORTS INCREASED
CHANCES FOR EXCESSIVE HEAT ACROSS PARTS OF THE GREAT PLAINS AND SOUTHEASTERN
QUADRANT OF THE COUNTRY, WITH THE HEAT SHIFTING SOUTHWARD THROUGHOUT WEEK-2.
THE POTENTIAL FOR TROPICAL DISTURBANCES SOUTH OF BAJA CALIFORNIA MAY BRING
ENHANCED SURGES OF MOISTURE TO PARTS OF THE INTERIOR WEST RESULTING IN
INCREASED CHANCES FOR LOCALIZED FLOODING. EXPECTED PROLONGED HEAT AND DRY
CONDITIONS ARE LIKELY TO INCREASE THE RISK FOR RAPID ONSET DROUGHT (ROD) FOR
PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE
VALLEYS, AND SOUTHEAST, THU, AUG 24.
MODERATE RISK OF EXCESSIVE HEAT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, AND
SOUTHEASTERN QUADRANT OF THE CONUS, THU-SAT, AUG 24-26.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE CENTRAL AND SOUTHERN GREAT
PLAINS, AND SOUTHEASTERN QUADRANT OF THE CONUS, THU-WED, AUG 24-30.
FLOODING POSSIBLE FOR PARTS OF THE INTERIOR WEST.
RAPID ONSET DROUGHT RISK FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY.
DETAILED SUMMARY
FOR SATURDAY AUGUST 19 - WEDNESDAY AUGUST 23:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY AUGUST 24 - WEDNESDAY AUGUST 30: THERE CONTINUES TO BE GOOD MODEL
AGREEMENT INDICATING MID-LEVEL RIDGING ACROSS MUCH OF THE CONUS EXCLUDING THE
NORTHEASTERN QUADRANT WEAKENING THROUGHOUT THE PERIOD TRANSLATING TO DECREASING
CHANCES FOR HEAT OVER THE WEEK-2 PERIOD. THE HIGH RISK OF EXCESSIVE HEAT HAS
DECREASED IN COVERAGE COMPARED TO YESTERDAY FOR PARTS OF THE LOWER MISSISSIPPI
AND TENNESSEE VALLEYS, AND SOUTHEAST, AUG 24, PRIMARILY BASED ON WHERE THE
ECMWF PROBABILISTIC EXTREMES TOOL (PET) INDICATES AT LEAST A 60% CHANCE OF
EXCEEDING THE 85TH PERCENTILE CLIMATOLOGICALLY, FURTHER SUPPORTED BY THE
CALIBRATED HEAT INDEX TOOL. THE MODERATE RISK (>40% CHANCE) OF EXCESSIVE HEAT
HAS BEEN EXPANDED SLIGHTLY WESTWARD TO COVER MORE OF THE CENTRAL AND SOUTHERN
PLAINS DUE TO THE GEFS ENSEMBLE MEAN INDICATING THE GREATEST MID-LEVEL HEIGHTS
CENTERED OVER THE REGION AT THE BEGINNING OF THE PERIOD AND THE NATIONAL BLEND
OF MODELS (NBM) SHOWING MORE NEAR RECORD TEMPERATURES POSSIBLE ACROSS PARTS OF
TEXAS (IN ADDITION TO OVER THE LOWER MISSISSIPPI VALLEY). EAST OF THE GREAT
PLAINS, THIS AREA HAS ALSO BEEN SCALED BACK FURTHER SOUTH DUE TO WEAKER HEAT
SIGNALS IN TOOLS FURTHER NORTH COMPARED TO YESTERDAY. A BROADER AREA OF SLIGHT
RISK (>20% CHANCE) HAS BEEN DECREASED IN COVERAGE TO PARTS OF THE CENTRAL AND
SOUTHERN GREAT PLAINS, AND SOUTHEASTERN QUADRANT OF THE CONUS, THROUGHOUT
WEEK-2, WITH THE ANTICIPATION OF THE HEAT SHIFTING SOUTHWARD THROUGHOUT THE
PERIOD.
MULTIPLE ENSEMBLE MEANS SHOW A LESS FAVORABLE MID-LEVEL TROUGH ORIENTATION FOR
A STORM IMPACTING THE NORTHEAST COMPARED TO YESTERDAY. THEREFORE NO ASSOCIATED
PRECIPITATION OR WIND HAZARDS ARE POSTED TODAY. THERE IS HOWEVER SOME INCREASED
POTENTIAL FOR LOCALIZED HEAVY PRECIPITATION, FLOODING, AND HIGH WINDS ACROSS
COASTAL PORTIONS OF THE MID-ATLANTIC AND GULF COAST STATES DUE TO INCREASED
CHANCES FOR POSSIBLE TROPICAL DISTURBANCES FORMING OVER THE GULF OF MEXICO AND
WESTERN ATLANTIC. DUE TO INHERENT HIGH UNCERTAINTY AT THIS LEAD TIME REGARDING
THE DETAILS OF POSSIBLE TROPICAL DISTURBANCES AND POTENTIAL IMPACTS, RELATED
HAZARDS ARE NOT DESIGNATED AT THIS TIME BUT WILL BE MONITORED IN THE UPCOMING
DAYS.
SEVERAL MODEL SOLUTIONS CONTINUE TO SHOW THE POSSIBILITY OF A TROPICAL CYCLONE
SOUTH OF BAJA CALIFORNIA AT THE BEGINNING OF WEEK-2. THIS STORM IS LIKELY TO
TRIGGER A GULF OF CALIFORNIA MOISTURE SURGE, BRINGING ENHANCED LOWER-LEVEL
MOISTURE AND POTENTIALLY HEAVY RAINFALL TO PORTIONS OF THE WESTERN CONUS. THE
ECMWF PET SHOWS INCREASED SPATIAL COVERAGE ACROSS THIS REGION OF AT LEAST A 20%
CHANCE OF 3-DAY RAINFALL TOTALS EXCEEDING THE 85TH PERCENTILE AND HALF AN INCH
AT THE BEGINNING OF WEEK-2. THE CANADIAN PET INDICATES THESE SIGNALS SCOPED TO
ARIZONA AND THE GEFS PET CONTINUES TO BE SIGNIFICANTLY DRIER THAN THE OTHER
TOOLS. DUE TO THE HIGH UNCERTAINTY OF WHERE THE HEAVIEST RAINFALL WILL OCCUR, A
HEAVY PRECIPITATION HAZARD IS NOT SPECIFIED AT THIS TIME. HOWEVER, LOCALIZED
HEAVY RAINFALL COULD TRIGGER FLOODING IN SOME AREAS. THE POSSIBLE FLOOD RISK
HAS BEEN EXPANDED FURTHER NORTH TO COVER MORE AREAS OF IDAHO, WHERE THERE IS A
CONCERN FOR WET THUNDERSTORMS. IT IS WORTH NOTING THAT FLASH FLOODING CAN OCCUR
EVEN IN AREAS THAT DO NOT DIRECTLY RECEIVE RAINFALL DUE TO RUNOFF FROM
PRECIPITATION UPSTREAM.
A RAPID ONSET DROUGHT (ROD) RISK REMAINS POSTED ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY AND TEXAS DUE TO THE COMBINATION OF INCREASED 30-DAY
PRECIPITATION DEFICITS, LITTLE TO NO RAINFALL FAVORED IN THE NEXT TWO WEEKS,
AND HIGH EVAPOTRANSPIRATION RATES ASSOCIATED WITH THE ABOVE-NORMAL TEMPERATURES.
OVER ALASKA, NO HAZARDS ARE POSTED. MID-LEVEL TROUGHING FAVORED OVER THE BERING
SEA AND THE WESTERN MAINLAND IS EXPECTED TO BRING ABOVE-NORMAL PRECIPITATION
FOR PORTIONS OF THE MAINLAND EXCLUDING SOUTHEASTERN ALASKA, ALTHOUGH TOTALS ARE
NOT EXPECTED TO REACH HAZARDOUS THRESHOLDS.
FORECASTER: MELISSA OU
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