925
FXUS21 KWNC 071838
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JULY 07 2026
SYNOPSIS: HIGHLY AMPLIFIED MID-LEVEL HIGH PRESSURE IS FORECAST TO DEVELOP
ACROSS THE WESTERN AND CENTRAL CONTIGUOUS U.S. (CONUS) DURING WEEK-1 AND
PERSIST INTO WEEK-2. WHILE THERE IS SOME UNCERTAINTY IN THE DYNAMICAL MODELS
REGARDING THE WESTWARD PROGRESSION OF THIS FEATURE AND THE EXTENT OF MID-LEVEL
LOW PRESSURE DOWNSTREAM IN THE EAST, A BROAD AREA OF EXTREME HEAT IS LIKELY
ACROSS THE WESTERN, CENTRAL, AND SOUTHEASTERN CONUS THROUGHOUT THE PERIOD GIVEN
THE CLIMATOLOGICAL PEAK OF SUMMER TIME HEATING. THIS PATTERN IS ALSO EXPECTED
TO ENHANCE THE MONSOONAL CIRCULATION, POTENTIALLY BRINGING TROPICAL MOISTURE
AND A RISK OF HEAVY PRECIPITATION INTO PARTS OF THE SOUTHWESTERN CONUS.
HAZARDS
HIGH RISK OF EXTREME HEAT ACROSS PORTIONS OF THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY, WED-THU, JUL 15-16.
MODERATE RISK OF EXTREME HEAT ACROSS PORTIONS OF THE CALIFORNIA CENTRAL VALLEY,
SOUTHWEST, GREAT BASIN, AND THE ROCKIES, WED-FRI, JUL 15-17.
MODERATE RISK OF EXTREME HEAT ACROSS THE GREAT PLAINS, MISSISSIPPI VALLEY,
SOUTHEAST, AND CAROLINAS, WED-FRI, JUL 15-17.
SLIGHT RISK OF EXTREME HEAT ACROSS MUCH OF THE WESTERN AND CENTRAL CONUS AS
WELL AS THE SOUTHEAST, OHIO AND TENNESSEE VALLEYS, GREAT LAKES, AND THE
SOUTHERN MID-ATLANTIC, WED-SUN, JUL 15-19.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
ROCKIES AND DESERT SOUTHWEST, TUE-FRI, JUL 15-19.
DETAILED SUMMARY
FOR FRIDAY JULY 10 - TUESDAY JULY 14:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY JULY 15 - TUESDAY JULY 21: MULTIPLE MODEL ENSEMBLES DEPICT
ANOMALOUS RIDGING DEVELOPING ACROSS THE WESTERN AND CENTRAL CONUS AROUND THE
MIDDLE OF WEEK-1 AND PERSISTING INTO WEEK-2. WHILE THE RIDGE IS PREDICTED TO
PEAK IN STRENGTH PRIOR TO THE START OF WEEK-2, THE 0Z ECMWF AND GEFS ENSEMBLES
STILL DEPICT A 595-596 DM RIDGE CENTER AT THE OUTSET OF WEEK-2. THE CHALLENGE
IN TODAY'S FORECAST IS THE POSITIONING OF THE RIDGE AXIS. THE ECMWF ENSEMBLE
CONTINUES TO DEPICT A MORE EASTWARD ORIENTATION OF THE RIDGE, WITH ENHANCED
POSITIVE 500-HPA HEIGHT ANOMALIES (GREATER THAN 60 METERS) OVER PORTIONS OF THE
MIDWEST. CONVERSELY, THE GEFS DEPICTS MORE AMPLIFIED TROUGHING DEVELOPING OVER
EASTERN CANADA WHICH RESULTS IN A QUICKER RETROGRESSION OF THE RIDGING OVER THE
WESTERN CONUS, AND INCREASING NORTHWESTERLY MID-LEVEL FLOW INTO THE UPPER
MIDWEST AND OHIO VALLEY FAVORING RELATIVELY COOLER TEMPERATURES. THE FORECAST
LEANS MORE ON THE ECMWF DUE TO RECENT MODEL SKILL IN PERSISTING THE PREVIOUS
HEAT WAVE ACROSS THE EASTERN U.S.
AT THE START OF THE PERIOD, EXTREME HEAT IS FORECAST ACROSS MUCH OF THE GREAT
PLAINS AND MISSISSIPPI VALLEY UNDERNEATH THE AFOREMENTIONED RIDGE AXIS. IN
ADDITION, ENHANCED SUBTROPICAL RIDGING COMBINED WITH ABOVE-NORMAL SEA SURFACE
TEMPERATURES OVER THE EASTERN GULF OF AMERICA FAVOR EXTREME HEAT ACROSS
PORTIONS OF THE SOUTHEAST AND FLORIDA. THE ECMWF ENSEMBLE INDICATES
TEMPERATURES NEAR OR ABOVE 90 DEG F ACROSS THE GREAT LAKES AND OHIO VALLEY
EARLY IN WEEK-2, WITH THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) DEPICTING AT
LEAST A 40 PERCENT CHANCE MAXIMUM TEMPERATURES EXCEED THE 85TH CLIMATOLOGICAL
PERCENTILE ACROSS THE UPPER MIDWEST. HOWEVER, THE GEFS IS SUBSTANTIALLY COOLER
OVER THESE AREAS, AS A FRONTAL SYSTEM MOVES THROUGH THE REGION TIED TO
TROUGHING AMPLIFYING ACROSS EASTERN CANADA. THE GEFS SOLUTION WOULD FAVOR THE
LARGEST EXTREME HEAT RISK SHIFTING FARTHER TO THE WEST OVER THE GREAT PLAINS
AND WESTERN CONUS. A HIGH RISK OF EXTREME HEAT IS POSTED ACROSS PORTIONS OF THE
NORTHERN PLAINS AND THE ADJACENT AREAS OF THE UPPER MISSISSIPPI VALLEY, JUL
15-16, WHERE SKILL WEIGHTED HEAT RISK GUIDANCE INDICATES PROBABILITIES GREATER
THAN 50 PERCENT FOR HEAT INDEX VALUES TO EXCEED 100 DEG F TIED TO HIGHER THAN
NORMAL HUMIDITY FORECAST OVER THE REGION. THESE NORTHERN AREAS HAVE LOWER
THRESHOLDS FOR EXTREME HEAT COMPARED TO FARTHER SOUTH, JUSTIFYING THE HIGH
RISK. A MODERATE RISK FOR EXTREME HEAT IS POSTED ACROSS MUCH OF THE GREAT
PLAINS, MISSISSIPPI VALLEY, AND SOUTHEAST, JUL 15-17, WITH HEAT INDEX VALUES
POTENTIALLY ABOVE 105 DEG F ACROSS THE CENTRAL AND SOUTHERN PLAINS, AND ALONG
THE GULF COAST AND SOUTHEAST. THE NATIONAL BLEND OF MODELS (NBM) DEPICTS RECORD
HIGH MINIMUM TEMPERATURES ACROSS PARTS OF THE SOUTHEAST INTO FLORIDA,
INDICATING LITTLE OVERNIGHT RELIEF FROM THE HEAT. THE SLIGHT RISK OF EXTREME
HEAT IS EXTENDED FARTHER TO THE EAST ACROSS THE GREAT LAKES AND OHIO VALLEY,
JUL 15-19, CONSISTENT WITH THE ECMWF, BUT WITH CONFIDENCE DECREASED SOMEWHAT
DUE TO THE GEFS DEPICTION.
ELEVATED CHANCES OF EXTREME HEAT ARE ALSO FORECAST ACROSS MUCH OF THE WESTERN
CONUS, ALTHOUGH THERE IS ALSO UNCERTAINTY AS THE GEFS IS MUCH FASTER AND MORE
AGGRESSIVE, PARTICULARLY INTO THE NORTHWEST, AND BOTH THE GEFS AND ECMWF BEGIN
TO WEAKEN THE RIDGE AMPLITUDE BY THE SECOND HALF OF THE PERIOD. THERE IS A
DECENT SIGNAL IN THE UNCALIBRATED 0Z GEFS AND ECMWF ENSEMBLES FOR TEMPERATURES
ABOVE 100 DEG F ACROSS LOW ELEVATION AREAS OF THE GREAT BASIN AND ROCKIES, AND
POSSIBLY ABOVE 105 DEG F ACROSS THE CALIFORNIA CENTRAL VALLEY SUPPORTING A
MODERATE RISK FOR EXTREME HEAT, JUL 15-17. THE GEFS IS MORE PROGRESSIVE AT
POTENTIALLY PUSHING EXTREME HEAT FARTHER INTO THE PACIFIC NORTHWEST, ALTHOUGH
THE ECMWF IS GENERALLY COOLER, ALTHOUGH THE SLIGHT RISK WAS EXTENDED INTO THE
WILLAMETTE VALLEY OF OREGON WHERE THERE ARE SOME WEAK SIGNALS FOR TEMPERATURES
EXCEEDING 90 DEG F. THE DESERT SOUTHWEST IS ALSO DOWNGRADED TO A SLIGHT RISK
DUE TO THE POTENTIAL FOR MONSOON MOISTURE TO LOWER TEMPERATURES.
HIGH TEMPERATURES OVER THE SOUTHWEST IS LIKELY TO INDUCE THERMAL SURFACE LOW
PRESSURE WHICH COMBINED WITH THE RIDGE AXIS BECOMING POSITIONED NEAR THE FOUR
CORNERS, SHOULD PULL TROPICAL MOISTURE NORTHWARD INTO THE REGION, KICKING OFF
THE SOUTHWEST MONSOON SEASON. DYNAMICAL MODELS DEPICT THE POTENTIAL INITIATION
OF MONSOON CONVECTION AS WEEK-2 GETS UNDERWAY. THE ECMWF AND GEFS PETS DEPICT
20 TO 40 PERCENT CHANCES FOR RAINFALL EXCEEDING THE 85TH CLIMATOLOGICAL
PERCENTILE AND ONE-HALF INCH. A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED
FOR MUCH OF THE ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN ROCKIES AND DESERT
SOUTHWEST, JUL 15-19, CONSISTENT WITH THE PETS, AND THE UNCALIBRATED ECMWF AND
GEFS WHICH DEPICT ENHANCED PRECIPITATION EXTENDING NORTHWARD INTO UTAH AND
COLORADO. THE SIGNAL IS SOMEWHAT WEAKER OVER TOWARD THE END OF WEEK-2, TIED TO
SLOW WEAKENING OF THE MID-LEVEL RIDGE. IN ADDITION TO THE HEAVY RAIN THREAT,
MONSOONAL THUNDERSTORMS CAN ALSO PRODUCE DRY LIGHTNING, RESULTING IN INCREASED
WILDFIRE RISK.
FORECASTER: THOMAS COLLOW
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