043
FXUS21 KWNC 181813
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 18 2023
SYNOPSIS: STRONG MID-LEVEL HIGH PRESSURE IS FORECAST THROUGHOUT MUCH OF THE
WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS), WHICH IS EXPECTED TO SUSTAIN THE
EXCESSIVE HEAT THREAT MAINLY THROUGHOUT THE SOUTHWEST, WITH INCREASED CHANCES
FOR EXCESSIVE HEAT OVER PARTS OF THE MIDWEST EARLY IN WEEK-2. THE COMBINATION
OF RECENT DRYNESS AND ABOVE-NORMAL TEMPERATURES FORECAST ACROSS THE GREAT
PLAINS SUPPORTS A CONTINUED RAPID ONSET DROUGHT (ROD) RISK OVER PARTS OF
WESTERN TEXAS.
HAZARDS
HIGH RISK OF EXCESSIVE HEAT FOR THE SOUTHWEST, SOUTHERN ROCKIES, AND SOUTHERN
HIGH PLAINS, WED, JUL 26.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF SOUTHWEST, CALIFORNIA, GREAT
BASIN, AND SOUTHERN PLAINS, WED-FRI, JUL 26-28.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE GREAT PLAINS AND MIDWEST,
WED-THU, JUL 26-27.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE CONUS EXCLUDING PORTIONS OF THE
NORTHEAST, MID-ATLANTIC, AND SOUTHEAST, WED-TUE, JUL 26-AUG 1.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE FLORIDA PENINSULA, WED-TUE, JUL 26-AUG 1.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF SOUTHERN TEXAS AND INTO LOUISIANA.
DETAILED SUMMARY
FOR FRIDAY JULY 21 - TUESDAY JULY 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JULY 26 - TUESDAY AUGUST 01: HEADING INTO WEEK-2, THERE IS GOOD
AGREEMENT IN THE DYNAMICAL MODEL 500-HPA HEIGHT FORECASTS FAVORING AMPLIFIED
RIDGING THROUGHOUT MUCH OF THE WESTERN AND NORTH-CENTRAL CONUS, WITH A
DEAMPLIFYING TROUGH OVER THE EASTERN CONUS. RELATIVE TO PREVIOUS GUIDANCE,
BOTH THE GEFS AND ECMWF ENSEMBLES HAVE COME INTO BETTER AGREEMENT IN REGARDS TO
THE TIMING OF A RELOADING TROUGH OVER THE EAST WHICH IS NOW FAVORED LATE IN
WEEK-2, BUT FEATURE A GRADUAL EXPANSION OF POSITIVE MID-LEVEL HEIGHT DEPARTURES
OVERSPREADING THE NORTH-CENTRAL CONUS BY LATE NEXT WEEK. AS A RESULT, THERE IS
HIGHER CONFIDENCE FOR WARMING WITH ABOVE-NORMAL SUMMER TEMPERATURES SHIFTING
EASTWARD RESULTING IN AN INCREASED RISK OF EXCESSIVE HEAT CONDITIONS OVER
PORTIONS OF THE MIDWEST.
WITH >597 DM MEAN HEIGHTS ESTABLISHED OVER THE SOUTHWESTERN CONUS ON DAY 8 (JUL
26), THERE IS CONTINUED AGREEMENT IN BOTH THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOLS (PETS) DEPICTING 50-60% CHANCES OF MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE FOCUSED OVER THE LOWER FOUR CORNERS. THEREFORE, A
HIGH RISK OF EXCESSIVE HEAT REMAINS POSTED FOR JUL 26, WHERE THERE ARE ELEVATED
CHANCES FOR DAYTIME TEMPERATURES EXCEEDING 110 DEG F ACROSS THE SONORAN DESERT,
100 DEG F TO THE EAST INTO SOUTHERN NEW MEXICO, AND 95 DEG F IN THE HIGHER
ELEVATIONS FURTHER NORTH. MUCH OF ANOMALOUS SOUTHWEST RIDGING ALOFT IS FAVORED
TO WEAKEN SOMEWHAT, THOUGH THE PETS CONTINUE TO MAINTAIN 40% CHANCES OF MAXIMUM
TEMPERATURES EXCEEDING THE 85TH PERCENTILE, SUPPORTIVE OF CONTINUING THE
MODERATE RISK OF EXCESSIVE HEAT THROUGH DAY 10 (JUL 28). COMPARED TO
YESTERDAY, THERE ARE DECREASED (INCREASED) HEAT SIGNALS IN THE PETS OVER PARTS
OF CALIFORNIA (TEXAS), AND THE MODERATE RISK AREA IS RESHAPED ACCORDINGLY.
TIED TO THE POSITIVE HEIGHT DEPARTURES TO THE NORTH, A SECOND MODERATE RISK
AREA OF EXCESSIVE HEAT REMAINS POSTED AND IS EXPANDED EASTWARD INTO PARTS OF
THE GREAT LAKES AND OHIO VALLEY WHERE THERE IS BETTER AGREEMENT BETWEEN THE
PETS INDICATING AT LEAST 30-40% CHANCES FOR MAXIMUM TEMPERATURES EXCEEDING THE
85TH PERCENTILE. ALTHOUGH THE GEFS PET HAS TENDED TO OVERFORECAST HEAT SIGNALS
IN THE MIDWEST, THE INCREASED POTENTIAL IS ALSO SUPPORTED BY UNCALIBRATED
TEMPERATURE TOOLS SHOWING DOUBLE-DIGIT POSITIVE TEMPERATURE DEPARTURES AS WELL
AS ADDED SIGNALS IN THE CALIBRATED HEAT RISK TOOLS IN THE HIGHLIGHTED REGION.
ACCOMPANYING THE EXPANDED HEAT POTENTIAL, A SLIGHT RISK OF EXCESSIVE HEAT
(7/26-8/1) IS ALSO EXPANDED EASTWARD, BUT EXCLUDES PARTS OF THE NORTHEAST AND
SOUTHEAST WHERE TEMPERATURES ARE NOT EXPECTED TO EXCEED HAZARD THRESHOLDS
DURING WEEK-2. OVER THE FLORIDA PENINSULA, PETS SHOW PERSISTENT 20-30% SIGNALS
FOR TEMPERATURES EXCEEDING THE 85TH PERCENTILE AND A SLIGHT RISK OF EXCESSIVE
HEAT IS CONTINUED FOR WEEK-2.
FOR PRECIPITATION, SIGNALS FOR ABOVE OR BELOW CONDITIONS CONTINUE TO BE QUITE
TENUOUS THROUGHOUT MUCH OF THE U.S. DURING THE PERIOD. FOR THE NORTH AMERICA
MONSOON REGION, THE ECMWF CONTINUES TO FAVOR A FAIRLY 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 TO INCREASE EVAPOTRANSPIRATION RATES THROUGH MUCH OF
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. OVER PARTS OF THE NORTHWESTERN CONUS, A SEPARATE ROD AREA
MAY BE ADDED IN UPCOMING HAZARD OUTLOOKS BASED ON ABOVE(BELOW)-NORMAL
TEMPERATURES (PRECIPITATION) BEING FAVORED WITH SOIL MOISTURE CONTENT
REGISTERING IN THE LOWEST PERCENTILES.
NO HAZARDS ARE POSTED FOR ALASKA DURING WEEK-2. ABOVE NORMAL TEMPERATURES ARE
FAVORED FOR MOST OF THE MAINLAND, WHILE NEAR NORMAL TEMPERATURES ARE INDICATED
FOR SOUTHEAST ALASKA.
FORECASTER: NICK NOVELLA
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