584
FXUS21 KWNC 171919
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 17 2023
SYNOPSIS: ANOMALOUS MID-LEVEL HIGH PRESSURE IS FORECAST THROUGHOUT MUCH OF THE
WESTERN 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 NORTH-CENTRAL CONUS EARLY IN WEEK-2. THE
COMBINATION OF RECENT DRYNESS AND ABOVE-NORMAL TEMPERATURES FORECAST ACROSS THE
GREAT PLAINS SUPPORTS EXPANSION OF THE 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, TUE-WED, JUL 25-26.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF SOUTHWEST, CALIFORNIA, GREAT
BASIN, NORTHERN INTERMOUNTAIN, AND SOUTHERN PLAINS, TUE-FRI, JUL 25-28.
MODERATE RISK OF EXCESSIVE HEAT FOR PARTS OF THE NORTHERN ROCKIES AND NORTHERN
HIGH PLAINS, TUE-WED, JUL 25-26.
SLIGHT RISK OF EXCESSIVE HEAT FOR MUCH OF THE WESTERN HALF OF THE CONUS,
TUE-MON, JUL 25-31.
SLIGHT RISK OF EXCESSIVE HEAT FOR THE FLORIDA PENINSULA, TUE-MON, JUL 25-31.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF SOUTHERN TEXAS AND INTO LOUISIANA.
DETAILED SUMMARY
FOR THURSDAY JULY 20 - MONDAY JULY 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY JULY 25 - MONDAY JULY 31: CONSISTENT WITH PREVIOUS ENSEMBLE
GUIDANCE, 500-HPA HEIGHT FORECASTS FROM THE GEFS AND ECMWF FAVOR AMPLIFIED
RIDGING THROUGHOUT THE WESTERN CONUS WITH DOWNSTREAM TROUGHING ACROSS THE
EASTERN CONUS BY EARLY NEXT WEEK. THIS LATTER MID-LEVEL FEATURE, AND AN
ASSOCIATED FRONTAL SYSTEM, IS EXPECTED TO BRING A SHOT OF COOLER AIR TO PROVIDE
RELIEF TO PARTS OF THE SOUTHEASTERN CONUS THAT HAVE EXPERIENCED BOUTS OF
EXCESSIVE HEAT THIS SUMMER. HOWEVER, MUCH OF THE HEAT THREAT REMAINS FAVORED TO
PERSIST ACROSS THE SOUTHWESTERN CONUS WITH AN INCREASED POTENTIAL FOR EXCESSIVE
EXTENDING NORTHWARD INTO THE GREAT BASIN AND GREAT PLAINS BEFORE ENSEMBLES
BEGIN TO DIVERGE ON THE EVOLUTION AND STRENGTH OF THE MID-LEVEL HEIGHT PATTERN
TOWARDS THE MIDDLE OF WEEK-2.
DURING THE FIRST FEW DAYS OF THE PERIOD, BOTH THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOLS (PETS) SHOW ELEVATED (50-60%) CHANCES OF MAXIMUM TEMPERATURES
EXCEEDING THE 85TH PERCENTILE TO SUPPORT A HIGH RISK OF EXCESSIVE HEAT OVER THE
LOWER FOUR CORNERS AND DESERT SOUTHWEST FOR JUL 25-26. IN THE HIGHLIGHTED AREA,
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. A BROADER MODERATE RISK AREA OF
EXCESSIVE HEAT IS ISSUED FOR JUL 25-28 FOR MUCH OF THE INTERIOR WEST, COVERING
THE CENTRAL VALLEY OF CALIFORNIA, AND PARTS OF THE NORTHERN INTERMOUNTAIN WHERE
PETS SHOW 30-40% OF TEMPERATURES EXCEEDING THE 85TH PERCENTILE. ALTHOUGH BOTH
THE GEFS AND ECMWF PETS ARE WEAKER WITH THE HEAT SIGNALS OVER NORTH-CENTRAL
CONUS, AN ADDITIONAL MODERATE RISK AREA IS POSTED FOR JUL 25-26 DUE TO GOOD
SUPPORT IN THE MODELS MAINTAINING STRONG MID-LEVEL RIDGING OVER THE NORTHERN
HIGH PLAINS, STRENGTHENING SIGNALS EMERGING OVER THE REGION IN HEAT RISK
PROTOTYPE TOOL (COURTESY OF NWS WESTERN REGION) LATE IN WEEK-1, AS WELL AS
UNCALIBRATED TEMPERATURE GUIDANCE FAVORING THE LARGEST TEMPERATURE ANOMALIES
(>10 DEGS F ABOVE-NORMAL) WITH ENSEMBLE MEAN TEMPERATURES EXCEEDING 95 DEG F
EARLY IN WEEK-2.
WITH MUCH OF THE ANOMALOUS RIDGING FAVORED TO REMAIN ESTABLISHED ACROSS THE
WEST THROUGH LATE JULY AND SUPPORT IN THE PETS, A BROAD SLIGHT RISK AREA OF
EXCESSIVE HEAT IS POSTED FOR THE ENTIRETY OF WEEK-2 FOR MUCH OF THE CONUS WEST
OF THE MISSISSIPPI. CONSIDERATION WAS GIVEN TO EXPAND THE CORRESPONDING SLIGHT
RISK AREA TO INCLUDE PORTIONS OF THE MIDWEST AND GREAT LAKES BASED ON RISING
MID-LEVEL HEIGHTS FAVORED IN THE GEFS LATER IN THE PERIOD. HOWEVER, THE ECMWF
FAVORS THE RETURN OF MORE TROUGHING, AND THE GEFS HAS TENDED TO OVER-FORECAST
ANOMALOUS WARMTH OVER THIS PART OF THE COUNTRY THIS SUMMER. GIVEN THESE
DISPARITIES IN THE GUIDANCE, NO EXCESSIVE HEAT HAZARDS ARE POSTED EAST OF THE
MISSISSIPPI, EXCEPT FOR OVER THE FLORIDA PENINSULA WHERE THERE IS CONTINUED
SUPPORT IN THE PETS TO MAINTAIN A SLIGHT RISK AREA FOR ALL OF WEEK-2.
FOR PRECIPITATION, NO HAZARDS ARE POSTED FOR THE U.S. DURING WEEK-2. THE ECMWF
SHOWS A SLIGHT TILT TOWARDS ABOVE-NORMAL PRECIPITATION OVER THE GREAT LAKES AND
OHIO VALLEY LIKELY TIED TO THE AFOREMENTIONED TROUGHING THAT IS FAVORED TO
DEVELOP LATE NEXT WEEK, THOUGH PRECIPITATION AMOUNTS ARE FAVORED TO REMAIN
BELOW HAZARDS CRITERIA AND THE GEFS FAVORS A DRIER SOLUTION. DIFFERENCES ALSO
EXIST IN REGARDS TO ANOMALOUS PRECIPITATION OVER THE NORTH AMERICA MONSOON
REGION WHERE THE ECMWF FAVORS A MORE SUPPRESSED MONSOONAL RIDGE AXIS COMPARED
TO THE GEFS. THOUGH INCREASED PRECIPITATION AMOUNTS ARE FAVORED, THERE IS
INSUFFICIENT SUPPORT IN THE TOOLS TO INCLUDE A CORRESPONDING HEAVY
PRECIPITATION OR FLOODING HAZARD AT THIS TIME.
THE ELEVATED RISK OF RAPID ONSET DROUGHT DEVELOPMENT IS CONTINUED FOR PARTS OF
THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY, DUE TO RECENT (IN SOME CASES
RECORD) HEAT IN RECENT WEEKS AND EXPECTED EXCESSIVE HEAT FORECAST TO PERSIST
INTO THE WEEK-2 PERIOD. A RISK OF RAPID ONSET DROUGHT (ROD) IS EXPANDED TO
INCLUDE PARTS OF WESTERN TEXAS SOUTH OF MIDLAND, WHERE LITTLE TO NO
PRECIPITATION AND WELL ABOVE-NORMAL TEMPERATURES ARE EXPECTED DURING THE NEXT
TWO WEEKS. 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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