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FXUS21 KWNC 201852
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 20 2023
SYNOPSIS: A MAJOR HEAT WAVE IS FORECAST TO BE ONGOING ACROSS MUCH OF THE
CONTIGUOUS U.S. (CONUS) DURING LATE JULY INTO EARLY AUGUST AS MID-LEVEL HIGH
PRESSURE BUILDS OVER MUCH OF THE WESTERN AND CENTRAL CONUS. EXCESSIVE HEAT IS
ALSO LIKELY TO EXPAND INTO PARTS OF THE NORTHEAST EARLY IN WEEK-2, BEFORE
DECREASING MID-LEVEL HEIGHTS MODERATE TEMPERATURES BY THE MIDDLE OF THE PERIOD.
THE COMBINATION OF RECENT DRYNESS AND PREDICTED ABOVE-NORMAL TEMPERATURES AND
BELOW-NORMAL PRECIPITATION DURING WEEK-2 SUPPORTS RAPID ONSET DROUGHT (ROD)
RISK OVER PARTS OF SOUTHERN TEXAS AND THE INTERIOR PACIFIC NORTHWEST. ROD RISK
IS ALSO ELEVATED ACROSS NORTHWESTERN NORTH DAKOTA DUE TO ANTECEDENT DRY
CONDITIONS AND LITTLE PRECIPITATION FORECAST DURING WEEK-1.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE SOUTHWEST, SOUTHERN ROCKIES,
AND SOUTHERN HIGH PLAINS, FRI, JUL 28.
HIGH RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, AND
THE EASTERN AREAS OF THE CENTRAL PLAINS, FRI-SAT, JUL 28-29.
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF SOUTHWEST, GREAT BASIN,
ROCKIES, GREAT PLAINS, MISSISSIPPI AND OHIO VALLEYS, AND THE GREAT LAKES,
FRI-MON, JUL 28-31.
MODERATE RISK OF EXCESSIVE HEAT FOR PORTIONS OF THE MID-ATLANTIC AND OHIO
VALLEY, FRI-SAT, JUL 28-29.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE CONUS EXCLUDING PORTIONS OF NEW
ENGLAND AND THE PACIFIC NORTHWEST, FRI-THU, JUL 28-AUG 3.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF SOUTHERN TEXAS AND INTO LOUISIANA,
INTERIOR PORTIONS OF THE PACIFIC NORTHWEST, AND NORTHWESTERN NORTH DAKOTA.
DETAILED SUMMARY
FOR SUNDAY JULY 23 - THURSDAY JULY 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR FRIDAY JULY 28 - THURSDAY AUGUST 03: ONE OF THE HALLMARKS ASSOCIATED WITH
THE ONGOING HEAT EVENT AFFECTING THE SOUTHERN TIER OF THE U.S. THIS SUMMER HAS
BEEN ITS ENDURANCE, AND UNFORTUNATELY THAT ASPECT LOOKS TO CHANGE VERY LITTLE
HEADING INTO LATE JULY AND EARLY AUGUST. BOTH THE 0Z ECMWF AND GEFS ENSEMBLES
INDICATE BROAD RIDGING EXPANDING THROUGHOUT MUCH OF THE CONUS EARLY IN WEEK-2,
WITH THE HIGHEST MID-LEVEL HEIGHTS (597-DM) OVER THE FOUR CORNERS. HEAT SIGNALS
APPEAR TO FINALLY BEGIN TO DIMINISH ACROSS THE WEST LATER IN WEEK-2 AS THE
NORTH AMERICAN MONSOON IS FORECAST TO BECOME MORE ACTIVE, WHILE THE STRONGEST
CHANCES FOR EXCESSIVE HEAT LOOK TO SHIFT EAST ACROSS THE PLAINS AND MISSISSIPPI
VALLEY. THE LARGEST CHANGE COMPARED TO YESTERDAY IS THE NOTABLE INCREASE IN
HEAT SIGNALS ACROSS THE EASTERN CONUS, INCLUDING PORTIONS OF THE OHIO VALLEY,
MID-ATLANTIC, AND NORTHEAST, AREAS WHICH HAVE FOR THE MOST PART BEEN SPARED OF
THE STRONGEST HEAT THROUGHOUT THE SUMMER.
THE PROBABILISTIC EXTREMES TOOLS (PETS) MAINTAIN 50-60 PERCENT CHANCES OF
MAXIMUM TEMPERATURES EXCEEDING THE 85TH PERCENTILE FROM THE DESERT SOUTHWEST TO
THE SOUTHERN PLAINS LINGERING EARLY INTO WEEK-2 BEFORE DROPPING BELOW 50
PERCENT ON DAY-9 (JUL 29). GIVEN THE TREND OF HIGH HEAT SIGNALS PERSISTING IN
THE REGION, A HIGH RISK OF EXCESSIVE HEAT REMAINS HIGHLIGHTED ON DAY-8 (JUL
28). IN THE HIGHLIGHTED HIGH RISK AREA, THERE REMAINS ELEVATED CHANCES FOR
DAYTIME TEMPERATURES EXCEEDING 110 DEG F ACROSS THE SONORAN DESERT, 100 DEG F
EASTWARD ALONG THE U.S./MEXICO BORDER INTO WESTERN TEXAS, AND 95 DEG F IN THE
HIGHER ELEVATIONS FURTHER NORTH. WHILE HEAT SIGNALS IN THE WEST HAVE DIMINISHED
SOMEWHAT COMPARED TO YESTERDAY, THEY HAVE INCREASED ACROSS PORTIONS OF THE
CENTRAL AND EASTERN CONUS. THE GEFS PET INDICATES AT LEAST A 60 PERCENT CHANCE
MAXIMUM TEMPERATURES EXCEED THE 85TH PERCENTILE ACROSS PARTS OF THE MIDDLE
MISSISSIPPI VALLEY, WITH THE ECMWF PET ALSO INDICATING PROBABILITIES OF AROUND
40-50 PERCENT. DUE TO THESE INCREASED SIGNALS IN THE PETS, ALONG WITH ACTUAL
TEMPERATURES PREDICTED TO BE AT LEAST 10 DEG F ABOVE-NORMAL IN THE UNCALIBRATED
GEFS, ECMWF, AND CANADIAN ENSEMBLES, A HIGH RISK FOR EXCESSIVE HEAT IS POSTED
ACROSS THE MIDDLE MISSISSIPPI VALLEY FOR DAYS 8 AND 9 (JUL 28-29). A BROADER
MODERATE RISK FOR EXCESSIVE HEAT CONTINUES ACROSS PORTIONS OF THE SOUTHWEST,
GREAT PLAINS, AND MISSISSIPPI VALLEY THROUGH JUL 31. THE GEFS AND ECMWF PETS
ALSO DEPICT STRONGER SIGNALS FOR HEAT ACROSS THE EASTERN CONUS COMPARED TO
YESTERDAY, WITH AT LEAST 40 PERCENT PROBABILITIES FOR TEMPERATURES EXCEEDING
THE 85TH PERCENTILE OVER PARTS OF THE OHIO VALLEY AND MID-ATLANTIC. THEREFORE,
A SEPARATE MODERATE RISK IS DESIGNATED ACROSS THESE AREAS FOR JUL 28-29 AS THE
HEAT IS FAVORED TO BE TRANSIENT AS EXPANDING TROUGHING ACROSS EASTERN CANADA
FAVORS A MODERATION IN TEMPERATURES ACROSS THESE AREAS BY THE MIDDLE OF WEEK-2.
HOWEVER, IT IS LOOKING INCREASINGLY LIKELY THAT SOME OF THE HOTTEST
TEMPERATURES OF THE SUMMER MAY OCCUR DURING THIS TIME FRAME, WITH ACTUAL
TEMPERATURES POSSIBLY WELL INTO THE 90S DEG F AND HEAT INDICES GREATER THAN 105
DEG F. THE SLIGHT RISK OF EXCESSIVE HEAT REMAINS POSTED FOR MUCH OF THE CONUS
FOR ALL OF WEEK-2, EXCLUDING ONLY PARTS OF NEW ENGLAND AND THE PACIFIC
NORTHWEST.
FOR PRECIPITATION, SIGNALS FOR ABOVE-NORMAL RAINFALL CONTINUE TO BE QUITE
TENUOUS THROUGHOUT MUCH OF THE U.S. DURING THE PERIOD, ALTHOUGH OCCASIONAL
FRONTAL DISTURBANCES ARE LIKELY TO BRING OCCASIONAL HEAVY PRECIPITATION AND
THUNDERSTORMS INTO PARTS OF THE NORTH-CENTRAL AND NORTHEASTERN CONUS. FOR THE
NORTH AMERICAN MONSOON REGION, THE ECMWF CONTINUES TO FAVOR A SLIGHTLY
SUPPRESSED RIDGE AXIS, TRANSLATING INTO LOWER PRECIPITATION AMOUNTS IN THE
UNCALIBRATED GUIDANCE COMPARED TO THE GEFS. WHILE LOCALLY HEAVY AMOUNTS ARE
POSSIBLE DURING WEEK-2, THERE IS INSUFFICIENT SUPPORT IN THE TOOLS TO INCLUDE A
CORRESPONDING HEAVY PRECIPITATION OR FLOODING HAZARD AT THIS TIME.
DUE TO LITTLE TO NO RAINFALL FORECAST AND THE ONGOING EXCESSIVE HEAT CONDITIONS
FAVORED TO PERSIST ACROSS THE SOUTHERN TIER, THERE CONTINUES TO BE AN ELEVATED
RISK OF RAPID ONSET DROUGHT (ROD) DEVELOPMENT FOR PARTS OF THE SOUTHERN PLAINS
AND LOWER MISSISSIPPI VALLEY GIVEN THE INCREASED EVAPOTRANSPIRATION RATES.
ADDITIONAL ROD RISK AREAS ARE NOW INDICATED ACROSS INTERIOR PORTIONS OF THE
PACIFIC NORTHWEST AND NORTHWESTERN NORTH DAKOTA DUE TO SOIL MOISTURES IN BOTH
OF THESE REGIONS BEING BELOW THE 30TH CLIMATOLOGICAL PERCENTILE AND WITH LITTLE
ADDITIONAL RAINFALL FORECAST DURING WEEK-1.
NO HAZARDS ARE POSTED FOR ALASKA DURING WEEK-2. NEAR- TO ABOVE-NORMAL
TEMPERATURES ARE FAVORED ACROSS THE STATE, ALONG WITH NEAR- TO ABOVE-NORMAL
PRECIPITATION.
FORECASTER: THOMAS COLLOW
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