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FXUS21 KWNC 061847
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 06 2025
SYNOPSIS: THE FAVORED DEVELOPMENT OF MID-LEVEL HIGH PRESSURE ACROSS CENTRAL
NORTH AMERICA NEXT WEEK IS ANTICIPATED TO RESULT IN A PATTERN CHANGE, WITH
ABOVE-NORMAL TEMPERATURES RETURNING ACROSS PORTIONS OF THE CENTRAL CONTIGUOUS
U.S. (CONUS), AND POSSIBLE EXTREME HEAT CONDITIONS EMERGING ACROSS PARTS OF THE
GREAT PLAINS, MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS DURING WEEK-2.
LINGERING MID-LEVEL LOW PRESSURE FORECAST OVER THE WESTERN THIRD OF THE CONUS
EARLY IN THE PERIOD FAVORS INCREASED CHANCES FOR EPISODES OF HIGH WINDS OVER
THE WEST COAST AND PARTS OF THE INTERIOR WEST. A STALLED FRONTAL BOUNDARY
REMAINS FORECAST ACROSS THE SOUTHEASTERN U.S. BRINGING AN INCREASED LIKELIHOOD
FOR ENHANCED PRECIPITATION AND HIGH WINDS. SURFACE LOW PRESSURE IS FORECAST TO
BRING INCREASED CHANCES OF ELEVATED WIND SPEEDS TO SOUTHERN AND SOUTHEASTERN
COASTAL ALASKA.
HAZARDS
SLIGHT RISK OF EXTREME HEAT ACROSS PORTIONS OF THE EASTERN GREAT PLAINS, MIDDLE
AND LOWER MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, AND SOUTHERN GREAT LAKES,
SUN-THU, SEP 14-18.
SLIGHT RISK OF HIGH WINDS OVER PARTS OF THE WEST COAST AND PORTIONS OF THE
INTERIOR WEST, SUN-MON, SEP 14-15.
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE FLORIDA PENINSULA AND COASTAL
SOUTHEAST, SUN-THU, SEP 14-18.
SLIGHT RISK OF HIGH WINDS ACROSS THE CENTRAL AND EASTERN GULF COAST, AND THE
LOWER EASTERN SEABOARD, SUN-THU, SEP 14-18.
SLIGHT RISK OF HIGH WINDS ACROSS COASTAL PORTIONS OF SOUTHERN AND SOUTHEASTERN
ALASKA, SUN-THU, SEP 14-18.
RAPID ONSET DROUGHT RISK ACROSS PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE
VALLEYS.
DETAILED SUMMARY
FOR TUESDAY SEPTEMBER 09 - SATURDAY SEPTEMBER 13:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SUNDAY SEPTEMBER 14 - SATURDAY SEPTEMBER 20: THE WEEK-2 HAZARDS PERSPECTIVE
REMAINS MOSTLY ON TRACK SINCE YESTERDAY. DYNAMICAL MODELS CONTINUE TO ADVERTISE
A STRONGLY AMPLIFIED RIDGE OVER CENTRAL CANADA, BOOKENDED BY A PAIR OF MEAN
TROUGHS OVER THE GULF OF ALASKA AND OVER EASTERN NORTH AMERICA NEXT WEEKEND.
AT THIS LEAD, THE PREDICTED HEIGHT PATTERN NEARLY RESEMBLES A CLASSIC
OMEGA-BLOCK PRESENTATION, WHICH IMPLIES THE POTENTIAL FOR ABOVE-NORMAL
TEMPERATURES TO PERSIST WELL BEYOND MID-SEPTEMBER FOR NEARLY THE ENTIRE CONUS
WEST OF THE APPALACHIANS. WHILE TROUGHING OVER THE GULF OF ALASKA LOOKS TO
REMAIN FAIRLY POTENT AT LEAST THROUGH THE MIDDLE OF WEEK-2, THE MOST NOTABLE
MID-LEVEL FEATURE IS THE 500-HPA CANADIAN RIDGE, WHERE THE 0Z ECMWF ENSEMBLE IN
PARTICULAR, NOW FAVORS A MEAN HEIGHT ANOMALY IN EXCESS OF 240 DAM ALONG AND TO
THE WEST OF HUDSON BAY, WITH THE RIDGE AXIS EXTENDING DEEPER INTO THE CONUS
FROM THIS ANOMALY CENTER COMPARED TO YESTERDAY. THESE CHANGES ALOFT TRANSLATE
WELL AT THE SURFACE, AS BOTH RAW AND CALIBRATED TEMPERATURE TOOLS DEPICT A
LARGER COVERAGE OF POSITIVE TEMPERATURE ANOMALIES FROM THE ROCKIES TO THE
APPALACHIANS EARLY IN WEEK-2. DUE TO LOWERING SUN ANGLES WITH THE AUTUMN
EQUINOX SOON APPROACHING, DAYTIME TEMPERATURES ARE NOT EXPECTED TO REACH
HAZARDOUS THRESHOLDS ACROSS THE HIGHER LATITUDES OF THE CONUS IN PROXIMITY TO
THE CANADIAN RIDGE, HOWEVER A SLIGHT RISK OF EXTREME HEAT REMAINS ISSUED FOR
MANY PARTS OF THE EASTERN PLAINS, MISSISSIPPI, TENNESSEE AND OHIO VALLEYS WHERE
THE PROBABILISTIC EXTREMES TOOLS (PETS) INDICATE AT LEAST 20% CHANCES FOR
MAXIMUM TEMPERATURES EXCEEDING THE 90TH PERCENTILE AND 90 DEGREES F. DUE TO
MORE PERSISTENT AND STRONGER RIDGING FAVORED, THIS SLIGHT RISK AREA IS EXTENDED
THROUGH SEP 18, AND EXPANDED FURTHER SOUTH TO INCLUDE PORTIONS OF THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY WHERE THERE ARE HIGHER CHANCES FOR DAYTIME
TEMPERATURES EXCEEDING 95 DEGREES F IN THE PETS WHICH COULD TRIGGER HEAT
ADVISORIES FOR MID-SEPTEMBER FOR THIS PART OF THE COUNTRY. IN ADDITION TO THE
ABOVE-NORMAL TEMPERATURES, THE COMBINATION OF BELOW-NORMAL PRECIPITATION
FORECAST SUPPORTS A RAPID ONSET DROUGHT (ROD) RISK, AND REMAINS POSTED MAINLY
OVER PARTS OF MISSISSIPPI AND ALABAMA. WITHIN THIS AREA, MANY LOCAL AREAS ARE
REGISTERING LESS THAN HALF THEIR NORMAL RAINFALL ACCUMULATION OVER THE PAST 60
DAYS.
UPSTREAM, BOTH THE GEFS AND ECMWF ENSEMBLES ARE BEGINNING TO INDICATE
ADDITIONAL SHORTWAVE ENERGY EJECTING EASTWARD FROM THE EASTERN PACIFIC TO
INDUCE MORE ONSHORE FLOW AND UNSETTLED WEATHER INTO PARTS OF THE WESTERN CONUS
BY THE OUTSET OF WEEK-2. BASED ON THE LINGERING SIGNALS FOR WIND SPEEDS
EXCEEDING THE 85TH PERCENTILE IN THE PETS, A SLIGHT RISK OF HIGH WINDS REMAINS
POSTED AND VALID THROUGH SEP 15, WITH ITS COVERAGE NOW FOCUSED ON THE WEST
COAST AND PARTS OF THE INTERIOR WEST IN THE UPDATED OUTLOOK. ANY ADDITIONAL
EPISODES OF HIGH WINDS COULD PROLONG THE RISK FOR WILDFIRE DEVELOPMENT DUE TO
VERY LOW SOIL MOISTURE VALUES BEING REGISTERED FOR MANY PARTS OF THE WEST.
RENEWED ONSHORE FLOW IS LIKELY TO BRING ENHANCED PRECIPITATION AMOUNTS FOR MUCH
OF THE NORTHWESTERN CONUS, WHERE THE ECMWF PET MAINTAINS CONSIDERABLY HIGH
(40-60%) SIGNALS FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE EARLY IN
WEEK-2. BY COMPARISON, THE GEFS PET IS MUCH MORE MUTED WITH THIS POTENTIAL, AND
GIVEN THAT THESE ELEVATED SIGNALS IN PERCENTILE SPACE ARE MORE THE RESULT OF
LOW PRECIPITATION CLIMATOLOGIES IN THE NORTHWESTERN CONUS, AND ACTUAL AMOUNTS
FAVORED TO REMAIN BELOW HAZARDOUS THRESHOLDS IN BOTH PETS, NO CORRESPONDING
PRECIPITATION HAZARDS ARE ISSUED. IF ANYTHING, ANY RAINFALL ABOVE CLIMATOLOGY
WOULD PROVIDE NEEDED RELIEF TO MANY AREAS IN THE NORTHWESTERN CONUS THAT ARE
EXPERIENCING MODERATE TO EXTREME DROUGHT CONDITIONS BASED ON THE LATEST U.S.
DROUGHT MONITOR.
OVER THE SOUTHEASTERN CONUS, STALLED FRONTAL ACTIVITY PREDOMINATELY FAVORED
DURING WEEK-1 LOOKS TO PERSIST INTO WEEK-2, SERVING AS A FOCUS FOR CONTINUED
ENHANCED PRECIPITATION ACROSS PARTS OF THE GULF COAST AND LOWER EASTERN
SEABOARD. OVER THE PAST FEW DAYS, THE UNCALIBRATED ECMWF AND THE ECMWF PET
CONTINUES TO TREND SOUTHWARD WITH THE HEAVY PRECIPITATION POTENTIAL DUE TO A
MORE PROGRESSIVE FRONT ADVANCING DEEPER INTO THE GULF OF AMERICA, WHEREAS THE
GEFS MAINTAINS MORE OF A NORTHERLY SOLUTION OF THE HEAVY PRECIPITATION OVER THE
SOUTHEAST. BASED ON THE FAVORED PERSISTENCE OF THIS SURFACE FEATURE, WITH
BETTER ENSEMBLE SUPPORT FOR WEAKNESSES IN THE HEIGHT PATTERN UNDERNEATH THE
RIDGE, A SLIGHT RISK OF HEAVY PRECIPITATION REMAINS ISSUED MAINLY OVER THE
FLORIDA PENINSULA AND INTO THE COASTAL GEORGIA, WITH A BROADER SLIGHT RISK AREA
OF HIGH WINDS FROM THE CENTRAL GULF TO THE LOWER MID-ATLANTIC. FOLLOWING A WET
WEEK-1 OVER FLORIDA (WITH MUCH OF THE PANHANDLE FORECAST TO RECEIVE OVER 3
INCHES BASED ON WPC QPF), ANY HEAVY RAINFALL MAY TRIGGER ISOLATED FLASH
FLOODING DURING THE WEEK-2 PERIOD. CONSISTENT WITH PREVIOUS THINKING, SURFACE
LOW FORMATION ALONG THE FRONTAL BOUNDARY CANNOT BE RULED OUT, WHICH IF
REALIZED, COULD BRING A RENEWED THREAT OF RAINFALL AND HIGH WINDS LATER IN
WEEK-2.
ACROSS THE MAIN DEVELOPMENT REGION (MDR), THE NATIONAL HURRICANE CENTER (NHC)
CONTINUES TO MONITOR A TROPICAL DISTURBANCE (INVEST 91L) WITH A 20% CHANCE FOR
DEVELOPMENT DURING THE SEVEN DAYS. ALTHOUGH ODDS OF FORMATION HAVE DRASTICALLY
DROPPED SINCE YESTERDAY TIED TO NEARBY DRY AIR MASS IN THE TROPICAL ATLANTIC,
THIS POTENTIAL SYSTEM WILL CONTINUE TO BE MONITORED, AS WELL AS ANY OTHER
POTENTIAL TROPICAL WAVES THAT MAY FORM, AS THE NEXT TWO WEEKS COINCIDE WITH THE
CLIMATOLOGICAL PEAK OF THE ATLANTIC HURRICANE SEASON. IN THE EASTERN PACIFIC,
THE ECMWF PROBABILISTIC TROPICAL CYCLOGENESIS TOOL CONTINUES TO SUPPORT
ADDITIONAL TROPICAL CYCLONE DEVELOPMENT TO THE SOUTH AND WEST OF MEXICO, WHICH
COULD POSSIBLY TRIGGER A GULF OF CALIFORNIA SURGE EVENT INTO THE DESERT
SOUTHWEST IN WEEK-2. THE ECWMF ENSEMBLE FAVORS AN ENHANCEMENT OF
MID-TROPOSPHERIC MOISTURE INTO THE LOWER FOUR CORNERS, ALONG WITH INCREASED
CHANCES (20-30%) FOR 3-DAY PRECIPITATION AMOUNTS EXCEEDING THE 85TH PERCENTILE
THROUGH THE MIDDLE OF WEEK-2. HOWEVER, THE GEFS IS LARGELY UNSUPPORTIVE OF A
HEAVY PRECIPITATION RISK, RESULTING IN NO PRECIPITATION RELATED HAZARDS, THOUGH
THIS POTENTIAL WILL CONTINUE TO BE MONITORED IN UPCOMING OUTLOOKS.
MEAN TROUGHING FAVORED OVER THE GULF OF ALASKA, AND ASSOCIATED MEAN SURFACE LOW
PRESSURE LOOKS TO BRING ENHANCED PRECIPITATION WITH POTENTIALLY HAZARDOUS HIGH
WINDS TO PARTS OF SOUTH-CENTRAL AND SOUTHEASTERN COASTAL ALASKA DURING WEEK-2.
RELATIVE TO YESTERDAY, THE ECMWF PET DEPICTS HIGHER CHANCES (40%-60%) OF WIND
SPEEDS EXCEEDING THE 85TH CLIMATOLOGICAL PERCENTILE AND 40-MPH ACROSS SOUTHERN
AND SOUTHEASTERN COASTAL ALASKA. BY CONTRAST, THE GEFS PET DEPICTS A MORE
LIMITED AREA WITH ONLY 20% CHANCES FOR MEETING THIS CRITERIA. TO RECONCILE
THESE DIFFERENCES, A SLIGHT RISK OF HIGH WINDS REMAINS DESIGNED FOR THIS PART
OF ALASKA FOR SEP 14-18 BEFORE MUCH OF THE TROUGHING DEAMPLIFIES LATER IN
WEEK-2. NO ASSOCIATED PRECIPITATION RELATED HAZARDS ARE POSTED DUE TO THE PETS
SHOWING LITTLE TO NO SIGNAL FOR ACCUMULATED AMOUNTS REACHING HAZARDOUS
THRESHOLDS IN PERCENTILE SPACE.
FORECASTER: NICK NOVELLA
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