262
FXUS21 KWNC 171834
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 17 2025
SYNOPSIS: MID-LEVEL HIGH PRESSURE ACROSS MUCH OF THE WESTERN CONTIGUOUS U.S.
(CONUS) MAY BRING A BRIEF SHOT OF EXTREME HEAT TO THE DESERT SOUTHWEST AT THE
BEGINNING OF WEEK-2. MID-LEVEL LOW PRESSURE IS ANTICIPATED TO QUICKLY FOLLOW
BEHIND, SHIFTING EASTWARD, POTENTIALLY BRINGING THE FIRST HEAVY SNOW OF THE
SEASON TO NORTHERN PORTIONS OF THE CASCADES AND ROCKIES. MEANWHILE, SURFACE
HIGH PRESSURE OVER THE NORTH PACIFIC ADJACENT TO SURFACE LOW PRESSURE OVER THE
WESTERN CONUS COULD BRING PERIODS OF HIGH WINDS TO MUCH OF COASTAL CALIFORNIA
FOR ALL OF WEEK-2. RAPID ONSET DROUGHT REMAINS A RISK FOR PARTS OF THE
SOUTHEAST WHERE ABOVE-NORMAL TEMPERATURES AND LIMITED WEEK-1 PRECIPITATION ARE
FORECAST.
HAZARDS
SLIGHT RISK OF EXTREME HEAT FOR THE DESERT SOUTHWEST, THU, SEP 25.
SLIGHT RISK OF HEAVY SNOW ACROSS PARTS OF THE NORTHERN CASCADES AND NORTHERN
ROCKIES, FRI-MON, SEP 26-29.
SLIGHT RISK OF EPISODIC HIGH WINDS FOR COASTAL PORTIONS OF CALIFORNIA SOUTH OF
POINT MENDOCINO, THU-WED, SEP 25-OCT 1.
RAPID ONSET DROUGHT (ROD) RISK FOR PORTIONS OF MISSISSIPPI, ALABAMA, AND
GEORGIA.
DETAILED SUMMARY
FOR SATURDAY SEPTEMBER 20 - WEDNESDAY SEPTEMBER 24:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY SEPTEMBER 25 - WEDNESDAY OCTOBER 01: AT THE BEGINNING OF WEEK-2,
AMPLIFIED MID-LEVEL RIDGING IS ANTICIPATED TO BUILD ACROSS MUCH OF THE WESTERN
TWO-THIRDS OF THE CONUS, WITH UPSTREAM MID-LEVEL TROUGHING OVER THE NORTHEAST
PACIFIC. THIS RIDGE IS FAIRLY SHORT-LIVED WITH THE PATTERN SHIFTING EASTWARD
RESULTING IN A TRANSITION TO MID-LEVEL TROUGHING ACROSS THE NORTHWEST AND
RIDGING OVER THE EASTERN CONUS BY THE LATTER PART OF THE PERIOD.
POSITIVE 500-HPA HEIGHT ANOMALIES ARE ANTICIPATED OVER THE DESERT SOUTHWEST AT
THE BEGINNING OF THE PERIOD ASSOCIATED WITH AN AMPLIFIED MID-LEVEL RIDGE
SITUATED OVER THE NORTH-CENTRAL CONUS, RESULTING IN THE POTENTIAL FOR A
LATE-SEASON HEAT WAVE FOR THE REGION. MULTIPLE PROBABILISTIC EXTREMES TOOLS
(PETS) INDICATE AT LEAST A 20% CHANCE OF MAXIMUM TEMPERATURES EXCEEDING THE
90TH PERCENTILE CLIMATOLOGICALLY AND 105 DEG F, FURTHER SUPPORTED BY OTHER
GUIDANCE TOOLS SHOWING INCREASING SIGNALS FOR EXTREME HEAT. ADDITIONALLY,
ENHANCED DEWPOINT TEMPERATURES COULD RESULT IN HIGHER HEAT INDEX VALUES.
THEREFORE A SLIGHT RISK (20-40% CHANCE) OF EXTREME HEAT IS POSTED FOR PARTS OF
THE DESERT SOUTHWEST, SEP 25. THIS HEAT FEATURE IS LIKELY TO BE FAIRLY
SHORT-LIVED DUE TO AN ANTICIPATED PROGRESSIVE PATTERN.
UPSTREAM, AMPLIFIED MID-LEVEL TROUGHING IS ANTICIPATED TO FORM OVER THE
NORTHEASTERN PACIFIC AND SHIFT EASTWARD INTO THE WESTERN CONUS THROUGHOUT THE
BEGINNING OF WEEK-2. THIS PATTERN IN ADDITION TO PREDICTED SURFACE HIGH
PRESSURE NEAR THE WEST COAST AND ADJACENT SURFACE LOW PRESSURE OVER WEST COAST
STATES MAY RESULT IN A TIGHT PRESSURE GRADIENT AT THE SURFACE AND INCREASED
LIKELIHOOD FOR HIGH WINDS ACROSS THE WEST COAST. A SLIGHT RISK OF EPISODIC HIGH
WINDS IS HIGHLIGHTED FOR COASTAL PORTIONS OF CALIFORNIA SOUTH OF POINT
MENDOCINO FOR SEP 25-OCT 1, WHERE PETS INDICATE AT LEAST A 20% CHANCE OF WIND
SPEEDS EXCEEDING THE 85TH PERCENTILE AND 25 MPH.
IN ADDITION TO ENHANCED WINDS, MODELS DEPICT SIGNIFICANT MOISTURE TRANSPORT
INTO THE PACIFIC NORTHWEST AS THIS TROUGH MOVES INTO THE INTERIOR WEST. THIS IS
LIKELY TO RESULT IN PERIODS OF ENHANCED PRECIPITATION FOR MUCH OF THE
NORTHWESTERN CONUS THROUGH THE MIDDLE OF WEEK-2. WHILE LOW ELEVATION
ACCUMULATIONS (I.E. RAIN) ARE NOT LIKELY TO REACH HAZARDOUS THRESHOLDS, THERE
IS AN INCREASED LIKELIHOOD OF HEAVY SNOW ACROSS HIGH ELEVATION AREAS OF THE
NORTHERN CASCADES AND ROCKIES AS A COLDER AIRMASS MOVES IN WITH THE TROUGH,
POTENTIALLY DROPPING TEMPERATURES SUFFICIENTLY TO ALLOW FOR SNOW IN THE
MOUNTAINS. A SLIGHT RISK OF HEAVY SNOW IS HIGHLIGHTED FOR THE NORTHERN
CASCADES, AND PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES, SEP 26-29. THE GEFS
PET SHOWS AT LEAST A 20% CHANCE OF 3-DAY ACCUMULATIONS EXCEEDING THE 85TH
PERCENTILE FOR PORTIONS OF THE CENTRAL ROCKIES, AND UNCALIBRATED ENSEMBLE
SOLUTIONS FROM BOTH THE GEFS AND ECMWF INDICATE AT LEAST A 20% CHANCE OF SOME
LOCALIZED AREAS EXCEEDING 4 INCHES. WHILE INDICATED SNOW ACCUMULATIONS ARE NOT
PARTICULARLY LARGE, THIS WOULD BE UNUSUALLY EARLY TO RECEIVE THE FIRST
SIGNIFICANT SNOWS OF THE SEASON FOR THE REGION.
THERE CONTINUES TO BE AN INCREASED LIKELIHOOD OF ABOVE NORMAL TEMPERATURES
ACROSS MUCH OF THE CONUS. THE COMBINATION OF ABOVE-NORMAL TEMPERATURES, 30 TO
60-DAY PRECIPITATION DEFICITS, AND LIMITED PRECIPITATION FORECAST DURING THE
NEXT WEEK SUPPORTS A RAPID ONSET DROUGHT (ROD) RISK ACROSS MISSISSIPPI,
ALABAMA, AND GEORGIA. DRY VEGETATIVE FUELS IN THIS AREA TYPICALLY MEANS
INCREASED RISK OF WILDFIRES. THERE ARE SOME INDICATIONS THAT A WEAKNESS IN THE
SUBTROPICAL RIDGE MAY BEGIN TO BRING MORE PRECIPITATION TO THE REGION BY
WEEK-2. HOWEVER, THE CHANCES FOR ABOVE-NORMAL PRECIPITATION ARE QUITE LOW AT
THIS TIME BUT WILL BE MONITORED GOING FORWARD.
FORECASTER: DANNY BARANDIARAN
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