268
FXUS21 KWNC 171920
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 17 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 ACROSS MUCH OF THE CENTRAL AND
SOUTHERN GREAT PLAINS AND 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. 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 EASTERN PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHEAST, FRI-SAT, AUG 25-26.
MODERATE RISK OF EXCESSIVE HEAT FOR APPROXIMATELY THE SOUTHEASTERN QUARTER OF
THE CONUS, FRI-SUN, AUG 25-27.
SLIGHT RISK OF EXCESSIVE HEAT FOR PARTS OF THE SOUTHWEST, CENTRAL AND SOUTHERN
PORTIONS OF THE GREAT PLAINS AND MISSISSIPPI VALLEY, SOUTHERN OHIO AND
TENNESSEE VALLEYS, SOUTHERN HALF OF THE APPALACHIANS, SOUTHERN MID-ATLANTIC AND
SOUTHEAST, FRI-THU, AUG 25-31.
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 SUNDAY AUGUST 20 - THURSDAY AUGUST 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY AUGUST 25 - THURSDAY AUGUST 31: 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 HAS BEEN EXPANDED SLIGHTLY WESTWARD COMPARED TO
YESTERDAY, AND INCLUDES EASTERN PORTIONS OF THE SOUTHERN PLAINS, LOWER
MISSISSIPPI AND TENNESSEE VALLEYS, AND SOUTHEAST, FRI-SAT, AUG 25-26. THIS IS
BASED PRIMARILY ON THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) WHICH 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 CONTINUES TO AFFECT THE SOUTHEASTERN QUADRANT OF THE
CONUS, FRI-SUN, AUG 25-27. A BROADER SLIGHT RISK AREA FOR EXCESSIVE HEAT IS
INDICATED FOR PARTS OF THE SOUTHWEST, CENTRAL AND SOUTHERN PORTIONS OF THE
GREAT PLAINS AND MISSISSIPPI VALLEY, SOUTHERN OHIO AND TENNESSEE VALLEYS,
SOUTHERN HALF OF THE APPALACHIANS, SOUTHERN MID-ATLANTIC AND SOUTHEAST,
FRI-THU, AUG 25-31. THE NATIONAL BLEND OF MODELS (NBM) FORECASTS NEAR-RECORD OR
RECORD-BREAKING TEMPERATURES PRIMARILY ACROSS TEXAS AND THE LOWER MISSISSIPPI
VALLEY, WITH DAYTIME HIGH TEMPERATURES RANGING FROM THE UPPER 90’S TO ABOUT 105
DEG F, AND OVERNIGHT LOW TEMPERATURES RANGING FROM THE MID 70’S TO LOW 80’S.
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 AND 6Z GFS ENSEMBLE FAVOR 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. 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 TODAY, TO ALIGN WITH
THE LATEST U.S. DROUGHT MONITOR MAP.
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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