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FXUS21 KWNC 221814
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 22 2025
SYNOPSIS: THE MODEL ENSEMBLE MEANS (SHOWING DEAMPLIFICATION) ARE NOT CONSISTENT
WITH DETERMINISTIC MODEL RUNS (MAINTAINING AMPLITUDE). IT IS EXPECTED THAT THE
MID-LEVEL FLOW WILL REMAIN MODERATELY AMPLIFIED, BUT THE PLACEMENT AND TIMING
OF INDIVIDUAL FEATURES IS HIGHLY UNCERTAIN. NO HAZARDS ARE POSTED DUE TO THE
HIGH UNCERTAINTY AND THE LIKELIHOOD THAT ANY SYSTEMS AFFECTING THE CONTIGUOUS
UNITED STATES (CONUS) WILL NOT BRING CONDITIONS REACHING HAZARDS THRESHOLDS.
MOST OF THE CONUS WILL BE UNUSUALLY WARM THROUGH WEEK-2, BUT DUE TO THE TIME OF
YEAR, EXTREME HEAT IS NOT ANTICIPATED. PERIODS OF MODERATE TO HEAVY
PRECIPITATION IN THE NORTHWEST AND NORTHERN CALIFORNIA ARE NOT EXPECTED TO
REACH HAZARDS THRESHOLDS, NOR ARE THE WET AND WINDY CONDITIONS EXPECTED ACROSS
SOUTH-CENTRAL AND SOUTHEASTERN ALASKA. A TROPICAL CYCLONE MAY TRACK THROUGH THE
WESTERN NORTH ATLANTIC, BUT AT THIS TIME, IT LOOKS LIKE ANYTHING THAT DEVELOPS
WILL REMAIN WELL OFFSHORE. THIS SHOULD LIMIT IMPACTS TO ROUGH SURF, AND
POSSIBLY ISOLATED COASTAL HIGH WIND GUSTS.
HAZARDS
NO HAZARDS POSTED.
DETAILED SUMMARY
FOR THURSDAY SEPTEMBER 25 - MONDAY SEPTEMBER 29:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY SEPTEMBER 30 - MONDAY OCTOBER 06: TODAY’S MODEL ENSEMBLE MEANS FOR
500-HPA HEIGHTS INDICATE A STEADY DEAMPLIFICATION OF THE 500-HPA HEIGHT PATTERN
THAT INITIALLY STRETCHES FROM THE NORTH PACIFIC ACROSS NORTH AMERICA. HOWEVER,
THE DETERMINISTIC MODELS TELL A DIFFERENT STORY, WITH ALL MAINTAINING MORE
AMPLIFIED 500-HPA FEATURES THROUGH THE PERIOD. IT APPEARS AS THOUGH THE
APPARENT DEAMPLIFICATION IN THE ENSEMBLE MEANS IS THE RESULT OF A WIDE ARRAY OF
SOLUTIONS AMONG THE INDIVIDUAL MEMBERS, WITH HEIGHT ANOMALIES AVERAGING OUT
NEAR OR SLIGHTLY ABOVE NORMAL AT ANY GIVEN LOCATION. HOWEVER, WHILE SOME
AMPLITUDE IS EXPECTED TO BE MAINTAINED IN THE 500-HPA FLOW THROUGH WEEK-2, THE
MODEL-TO-MODEL AND RUN-TO-RUN INCONSISTENCY IN FORECAST SOLUTIONS RESULTS IN A
VERY LOW CONFIDENCE FORECAST. MOST OF THE RECENT DETERMINISTIC MODEL RUNS FORM
ONE OR MORE CLOSED 500-HPA LOWS OR SHORT-LIVED SHARP 500-HPA TROUGHS OVER NORTH
AMERICA AND/OR THE MID-LATITUDES OF THE OCEANS TO THE EAST AND WEST. THESE
MEANDER SOUTH OF ABOVE-NORMAL 500-HPA HEIGHTS ACROSS CANADA, BUT THE FORECAST
PLACEMENT AND TIMING OF THESE SYSTEMS DIFFER ALMOST RANDOMLY FROM RUN-TO-RUN
AND MODEL-TO-MODEL. IN ANY CASE, THESE SMALLER-SCALE FEATURES APPEAR TO HAVE
TRANSIENT EFFECTS AT ANY GIVEN LOCATION IN A FAIRLY PROGRESSIVE FLOW.
FROM A HAZARDS PERSPECTIVE, ANY CLOSED 500-HPA LOW AFFECTING PART OF THE CONUS
SHOULD BE WEAK, AND ANY SHORTWAVE ONLY BRIEFLY AMPLIFIED, SPINNING UP SOUTH OF
THE ANOMALOUSLY HIGH 500-HPA HEIGHTS OVER CANADA. AS A RESULT, THEY ARE
UNLIKELY TO BRING PRECIPITATION OR WIND REACHING HAZARDOUS THRESHOLDS, SO NO
PRECIPITATION OR WIND HAZARDS ARE POSTED. OVER THE COURSE OF WEEK-2, 500-HPA
HEIGHTS ARE FORECAST TO AVERAGE SLIGHTLY ABOVE NORMAL AT MOST LOCATIONS, AND
WITH ABOVE-NORMAL HEIGHTS OVER CANADA PRECLUDING ANY INTRUSIONS OF COLD AIR
FROM THE NORTH, TEMPERATURES ARE EXPECTED TO AVERAGE ABOVE NORMAL THROUGHOUT
THE CONUS; HOWEVER, PARTIALLY DUE TO THE TIME OF YEAR, RAW TEMPERATURES AND
HEAT INDEXES ARE EXPECTED TO REMAIN BELOW HAZARDS THRESHOLDS.
THERE IS FAIR MODEL AGREEMENT PLACING ONE OR MORE MID-LEVEL TROUGHS OVER OR
NEAR THE PACIFIC NORTHWEST DURING THE WEEK, FAVORING PERIODS OF ENHANCED
PRECIPITATION FOR MUCH OF THE CENTRAL AND NORTHERN WEST COAST REGION UNTIL AT
LEAST THE MIDDLE OF WEEK-2. A FEW INCHES OF PRECIPITATION MAY ACCUMULATE OVER
BOTH COASTAL AND HIGHER ELEVATION LOCATIONS IN WESTERN WASHINGTON AND
NORTHWESTERN OREGON. HOWEVER, THIS IS A FAVORED REGION FOR ENHANCED
PRECIPITATION WHEN THERE IS DECENT MID-LEVEL TROUGHING OFF THE NORTHWEST COAST,
SO THESE AMOUNTS ARE NOT MARKEDLY ATYPICAL, AND NO HAZARD IS POSTED.
A MODERATE AMOUNT OF TROPICAL MOISTURE MAY STREAM INTO THE MONSOONAL REGIONS OF
THE SOUTHWEST PERIODICALLY DURING WEEK-2, RESULTING IN ABOVE-NORMAL RAINFALL
THAT IS EXPECTED TO REMAIN BELOW HAZARDS THRESHOLDS.
THERE IS FAIR AGREEMENT AMONG THE MODELS THAT MID-LEVEL TROUGHING WILL BE
ESTABLISHED NEAR OR SOUTH OF ALASKA FOR AT LEAST PART OF WEEK-2, WHICH SHOULD
PRODUCE ONE OR MORE SURFACE STORMS TRACKING NEAR THE ALEUTIANS, THROUGH THE
GULF OF ALASKA, AND POSSIBLY INTO SOUTHEAST ALASKA. WITH HIGH SURFACE PRESSURE
EXPECTED TO PREVAIL WEST OF THE CONTIGUOUS UNITED STATES (CONUS), THIS SET-UP
WOULD FAVOR INCREASED SURFACE WINDS AND ABUNDANT MOISTURE TRANSPORT FROM THE
NORTH PACIFIC INTO SOUTH-CENTRAL AND SOUTHEASTERN ALASKA, WHICH IN TURN WOULD
ENHANCE CHANCES FOR HEAVY PRECIPITATION ACROSS THIS REGION. THE REMNANTS OF
TYPHOON NEOGURI, CURRENTLY IN THE CENTRAL PACIFIC, MAY ENHANCE THE MOISTURE
INFLUX, ALTHOUGH THIS IS FAR FROM CERTAIN. THE ENSEMBLE MEANS ALL SHOW OVER 4
INCHES OF RAIN FALLING ON A LARGE PART OF THIS AREA DURING WEEK-2, ALONG WITH
PERIODS OF GUSTY WINDS. HOWEVER, THIS IS THE WETTEST TIME OF THE YEAR IN THE
REGION, AND THE FORECAST PATTERN IS NOT TOO UNUSUAL. WEEKLY NORMALS EXCEED 2
INCHES ALMOST REGION-WIDE NOW, REACHING AS HIGH AS 6 INCHES IN CENTRAL
SOUTHEASTERN ALASKA ALONG THE IMMEDIATE COAST. THE PATTERN ALSO FAVORS STRONGER
WINDS THAN ARE TYPICAL FOR MOST OTHER PARTS OF THE CONTINENT. GIVEN THE
CLIMATOLOGY, NEITHER THE FORECAST PRECIPITATION TOTALS NOR WIND GUSTS ARE
EXPECTED TO REACH HAZARDS THRESHOLDS.
MANY OF THE DETERMINISTIC MODELS BRING A TROPICAL CYCLONE NORTHWARD IN THE
WESTERN NORTH ATLANTIC PARALLEL TO THE EAST COAST DURING THE EARLY TO MIDDLE
PART OF THE PERIOD. ALL MODELS KEEP ANY DEVELOPMENT SEVERAL HUNDRED MILES
OFFSHORE, SO IT’S LIKELY THAT ANY IMPACTS ON THE CONUS WILL BE LIMITED TO ROUGH
SURF AND POSSIBLY ISOLATED OCCURRENCES OF STRONG WIND GUSTS ALONG THE IMMEDIATE
COASTLINE. THERE ARE A FEW INDIVIDUAL MEMBERS OF ALL THE ENSEMBLES THAT SHOW
TROPICAL CYCLONES IN THE WESTERN ATLANTIC CLOSER TO THE EAST COAST, OR IN THE
GULF, BUT THE OVERWHELMING MAJORITY OF THE ENSEMBLE MEMBERS KEEP AREAS NEAR THE
CONUS AWAY FROM ANY TROPICAL CYCLONE IMPACTS, AND IN ANY CASE, THE MEMBERS
FORECASTING DEVELOPMENT SHOW NO RUN-TO-RUN CONSISTENCY ON PLACEMENT OR
STRENGTH. THIS POTENTIAL WILL BE MONITORED, BUT IT IS NOT THE FAVORED SOLUTION
AT THIS TIME GIVEN THE OVERWHELMING MAJORITY OF ENSEMBLE MEMBERS DO NOT
FORECAST A TROPICAL CYCLONE NEAR THE CONUS DURING WEEK-2.
FORECASTER: RICH TINKER
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