862
FXUS21 KWNC 181919
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 18 2023
SYNOPSIS: THE WEEK-2 PERIOD IS PREDICTED TO BE DOMINATED BY MID-LEVEL HIGH
PRESSURE ACROSS MUCH OF THE CONTIGUOUS U.S. (CONUS). WITH TIME, THIS AREA OF
MID-LEVEL HIGH PRESSURE IS EXPECTED TO SHIFT SOUTHWARD AND WEAKEN. THIS PATTERN
SUPPORTS INCREASED CHANCES FOR EXCESSIVE HEAT OVER APPROXIMATELY THE SOUTHERN
HALVES OF THE GREAT PLAINS AND MISSISSIPPI VALLEY, AND MUCH OF THE SOUTHEASTERN
QUADRANT OF THE LOWER 48 STATES. 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. CONTINUED
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 EASTERN TEXAS, THE LOWER MISSISSIPPI VALLEY,
AND SOUTHEAST, SAT, AUG 26.
MODERATE RISK OF EXCESSIVE HEAT FOR MUCH OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI VALLEY, AND SOUTHEAST, SAT-SUN, AUG 26-27.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE SOUTHWEST, THE SOUTHERN GREAT
PLAINS AND LOWER MISSISSIPPI VALLEY, TENNESSEE, AND MOST OF THE SOUTHEAST,
SAT-FRI, AUG 26-SEP 1.
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 MONDAY AUGUST 21 - FRIDAY AUGUST 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY AUGUST 26 - FRIDAY SEPTEMBER 01: THERE CONTINUES TO BE GOOD MODEL
AGREEMENT INDICATING MID-LEVEL RIDGING ACROSS MUCH OF THE CONUS (EXCLUDING THE
NORTHEASTERN QUADRANT) WEAKENING AND SHIFTING SOUTHWARD THROUGHOUT THE FORECAST
PERIOD. THIS TRANSLATES TO DECREASING ODDS FOR EXCESSIVE HEAT DURING WEEK-2.
THE HIGH RISK OF EXCESSIVE HEAT INCLUDES EASTERN TEXAS, THE LOWER MISSISSIPPI
VALLEY, AND PARTS OF THE SOUTHEAST, SAT, AUG 26. THIS IS BASED PRIMARILY ON THE
ECMWF AND GEFS PROBABILISTIC EXTREMES TOOLS (PET) WHICH INDICATE 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 CONTINUES TO AFFECT MUCH OF THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY,
AND SOUTHEAST, SAT-SUN, AUG 26-27. A BROADER SLIGHT RISK AREA FOR EXCESSIVE
HEAT IS INDICATED FOR PARTS OF THE SOUTHWEST, THE SOUTHERN GREAT PLAINS, AND
LOWER MISSISSIPPI VALLEY, TENNESSEE VALLEY, AND MOST OF THE SOUTHEAST, SAT-FRI,
AUG 26-SEP 1. THE NATIONAL BLEND OF MODELS (NBM) FORECASTS NEAR-RECORD OR
RECORD-BREAKING TEMPERATURES PRIMARILY ACROSS TEXAS, THE LOWER MISSISSIPPI
VALLEY, AND PARTS OF THE SOUTHEAST, WITH DAYTIME HIGH TEMPERATURES RANGING FROM
THE MID 90’S TO NEAR 110 DEG F, AND OVERNIGHT LOW TEMPERATURES RANGING FROM THE
MID 70’S TO LOW 80’S DEG F.
UNCERTAINTY REMAINS HIGH REGARDING THE POSSIBLE DEVELOPMENT AND FUTURE TRACK OF
A TROPICAL SYSTEM OVER THE GULF OF MEXICO DURING WEEK-2 OR EVEN LATER IN
WEEK-1. THE 0Z EUROPEAN ENSEMBLE FAVORS THE HEAVIEST RAINFALL ACROSS THE
WESTERN GULF COAST REGION AND THE RIO GRANDE VALLEY, WITH MUCH OF THIS
PRECIPITATION OCCURRING PRIOR TO THE BEGINNING OF WEEK-2. THE 0Z CANADIAN
ENSEMBLE FAVORS THE HEAVIEST RAINFALL ACROSS THE EASTERN HALF OF THE GULF COAST
REGION IN WEEK-2, AND THE GEFS PET DOESN’T DEPICT ANY AREAS NEAR THE GULF COAST
THAT HAVE AT LEAST A 20% CHANCE OF AMOUNTS EXCEEDING THE 85TH HISTORICAL
PERCENTILE AND TOTALING OVER 1-INCH FOR ANY GIVEN 3-DAY PERIOD WITHIN WEEK-2.
GIVEN THESE MODEL DIFFERENCES IN BOTH LOCATION AND TIMING OF ANY TROPICAL
SYSTEMS, NO PRECIPITATION HAZARD IS POSTED ON TODAY’S MAP.
DURING THE ANTECEDENT WEEK-1 PERIOD OVER THE EASTERN PACIFIC, HURRICANE HILARY
IS FORECAST TO TURN NORTHWARD AND BRING HEAVY RAINFALL AND GUSTY WINDS TO BAJA
CALIFORNIA, THE U.S. DESERT SOUTHWEST INCLUDING MUCH OF CALIFORNIA, AND THE
INTERMOUNTAIN WEST. THIS WILL LIKELY SET THE STAGE FOR LOCALIZED AND/OR
REGIONAL FLOODING ACROSS THESE AREAS, INCLUDING THE CONCERN FOR WET
THUNDERSTORMS AS FAR NORTH AS IDAHO, CONTINUING INTO THE WEEK-2 PERIOD.
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. THE ROD AREA WAS EXPANDED A BIT NORTHWARD TO ALIGN WITH THE
LATEST U.S. DROUGHT MONITOR MAP. HOWEVER, THE DEPICTED ROD SHAPE DEPENDS ON
WHETHER OR NOT ANY TROPICAL SYSTEMS DEVELOP AND MOVE ACROSS THAT REGION, WHICH
AT THE PRESENT TIME IS HIGHLY UNCERTAIN.
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: ANTHONY ARTUSA
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