947
FXUS21 KWNC 151821
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 15 2026
SYNOPSIS: MID-LEVEL HIGH PRESSURE BUILDING OVER SOUTH-CENTRAL CANADA IS
EXPECTED TO BRING CONTINUED WARMTH, BUT RELATIVELY QUIET WEATHER FOR MUCH OF
THE CONTIGUOUS U.S. (CONUS) DURING THE PERIOD. HOWEVER, MID-LEVEL LOW PRESSURE
SITUATED OFFSHORE OF THE WEST COAST, AS WELL AS LINGERING FRONTAL ACTIVITY
SUPPORTS AN INCREASED RISK OF HEAVY PRECIPITATION OVER THE PARTS OF THE FOUR
CORNERS, EASTERN GREAT PLAINS, AND THE EASTERN CONUS EARLY IN WEEK-2. A
CONTINUATION OF ENHANCED, AND POSSIBLY HEAVY PRECIPITATION FROM WEEK-1 INTO
WEEK-2 MAY LEAD TO FLOODING ACROSS PARTS OF THE FOUR CORNERS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, MID-ATLANTIC,
AND NORTHEAST, WED-SUN, SEP 23-27.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHWEST, SOUTHERN
ROCKIES, AND SOUTHERN HIGH PLAINS, WED-THU, SEP 23-24.
FLOODING POSSIBLE FOR PORTIONS OF THE FOUR CORNERS REGION.
DETAILED SUMMARY
FOR FRIDAY SEPTEMBER 18 - TUESDAY SEPTEMBER 22:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY SEPTEMBER 23 - TUESDAY SEPTEMBER 29: LATE IN WEEK-1, DYNAMICAL
MODELS CONTINUE TO FEATURE AN ANOMALOUS RIDGE CENTER SHIFTING EASTWARD TOWARDS
HUDSON BAY, WITH TROUGHING UPSTREAM OVER THE BERING SEA AND ALASKA. UNDERNEATH
THE RIDGE CENTER OVER CANADA, THERE ARE SOME INDICATIONS OF SHORTWARE ENERGY
PROPAGATING UNDERNEATH THE RIDGE CENTER ACROSS THE EASTERN CONUS, THOUGH BOTH
THE GEFS AND ECMWF AGREE IN FAVORING A SECONDARY TROUGH BECOMING MORE AMPLIFIED
OFF THE WEST COAST TOWARDS THE MIDDLE OF NEXT WEEK. HOWEVER, THE ECMWF AND GEFS
BEGIN TO DIVERGE WITH THE EVOLUTION OF THE PATTERN AT THIS LEAD, WITH THE
LATTER FAVORING RISING HEIGHTS OVER THE NORTHWESTERN CONUS, AND FORCING A
SHORTWAVE TROUGH OVER SOUTH-CENTRAL CANADA AND MORE OF MEAN CUTOFF LOW OFF THE
WEST COAST. THE ECMWF, ON THE OTHER HAND, MAINTAINS BROADER TROUGHING ACROSS
THE NORTHEASTERN PACIFIC, WITH A STRONGER AND MORE EXPANSIVE COVERAGE OF
POSITIVE HEIGHT DEPARTURES OVERSPREADING NEARLY TWO-THIRDS OF THE NORTH AMERICA
BY LATER NEXT WEEK. WHILE BOTH ENSEMBLES EVENTUALLY BECOME BETTER ALIGNED IN
FAVORING A MORE STABLE, OMEGA LIKE PATTERN LATER IN WEEK-2, DIFFERENCES IN
PHASING OF MEAN MID-LEVEL FEATURES AMONG THE MODELS EARLY IN THE PERIOD
PRECLUDES MUCH FORECAST CONFIDENCE IN THE UPDATED OUTLOOK.
IN RESPONSE TO THE STRONG RIDGING OVER SOUTHCENTRAL CANADA, ABOVE-NORMAL
TEMPERATURES ARE PREDOMINATELY FAVORED MAINLY EAST OF THE ROCKIES, WITH THE
STRONGEST TEMPERATURE ANOMALIES FEATURED OVER THE SOUTHEASTERN AND THROUGHOUT
THE NORTH-CENTRAL CONUS IN PROXIMITY TO THE RIDGE. EVEN WITH TEMPERATURES
CONTINUING TO GROW WARMER LATER NEXT WEEK, NO CORRESPONDING TEMPERATURE RELATED
HAZARDS ARE POSTED AS ACTUAL DAYTIME MAXIMUMS ARE EXPECTED TO REMAIN BELOW
HAZARD CRITERIA DUE TO DECREASING SUN ANGLES IN THE AUTUMN, WITH NOT MUCH
IMPACT ON DRYING SOILS EXPECTED.
ACROSS THE EASTERN CONUS, THERE CONTINUES TO BE AN INCREASED RISK OF HEAVY
PRECIPITATION ASSOCIATED WITH A LINGERING FRONTAL BOUNDARY DRAPED FROM THE
NORTHERN GULF INTO THE WESTERN ATLANTIC. CONSISTENT WITH PREVIOUS GUIDANCE, THE
HIGHEST PRECIPITATION AMOUNTS ARE FAVORED OFFSHORE, HOWEVER BOTH RAW AND
CALIBRATED PRECIPITATION TOOLS CONTINUE TO FEATURE INCREASED CHANCES FOR 3-DAY
AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH EARLY IN THE PERIOD. ONE
DIFFERENCE SINCE YESTERDAY CONCERNS FLORIDA AND THE EASTERN GULF, WHERE TOOLS
DEPICT A MORE COHERENT CONNECTION OF MOISTURE FROM THE TROPICS. AS A RESULT, A
SLIGHT RISK OF HEAVY PRECIPITATION REMAINS POSTED MUCH OF THE EASTERN SEABOARD
WITH COVERAGE ADDED ALONG THE EASTERN GULF, AND IS ALSO EXTENDED THROUGH SEP 27
BASED ON A PERSISTENCE OF SIGNALS IN THE TOOLS. THIS INCREASED RISK IS ALSO
SUPPORTED BY OBSERVED SEA SURFACE TEMPERATURES (SSTS) AND PRECIPITABLE WATER
ANALYSES WHICH ARE CURRENTLY REGISTERING IN THE HIGHEST CLIMATOLOGICAL
PERCENTILES (100TH AND 84TH, RESPECTIVELY) WITHIN THE GULF. WITH PROBABILISTIC
TROPICAL CYCLONE (TC) TOOLS AND ENSEMBLES ALSO SHOWING SOME SIGNAL FOR LOW
DEVELOPMENT OVER WESTERN ATLANTIC LATER NEXT WEEK, ANY LOW THAT DEVELOPS COULD
ACQUIRE TROPICAL CHARACTERISTICS DURING WEEK-2. THIS IS REFLECTED IN THE LATEST
GLOBAL TROPICS HAZARDS (GTH) OUTLOOK RELEASED TODAY, WITH 20% CHANCES OF TC
FORMATION ISSUED TO THE NORTH OF THE BAHAMAS IN THE WESTERN ATLANTIC.
TIED TO THE TROUGHING FAVORED OFF THE WEST COAST, A SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS POSTED OVER THE SOUTHWESTERN CONUS AND VALID THROUGH SEP
24 BEFORE MID-LEVEL HEIGHTS ARE FAVORED TO RISE LATER NEXT WEEK. FOLLOWING THE
TREND IN THE GUIDANCE SINCE YESTERDAY, THE SLIGHT RISK AREA IS AGAIN EXPANDED
EASTWARD TO INCLUDE MORE OF SOUTHERN AND CENTRAL PLAINS BASED ON INCREASED
SUPPORT IN THE TOOLS EARLY IN WEEK-2. A MODERATE RISK WAS CONSIDERED FOR
INCLUSION BASED ON STRONGER SIGNALS IN THE LATEST UNCALIBRATED ECMWF, WHICH NOW
DEPICTS POCKETS OF 30% CHANCES FOR 3-DAY AMOUNTS EXCEEDING AN INCH MAINLY OVER
THE SOUTHERN HIGH PLAINS. HOWEVER, THE GEFS MAINTAINS A CONSIDERABLY DRIER MEAN
SOLUTION OVER THIS PART OF THE COUNTRY, LIMITING FORECAST CONFIDENCE FOR A
HIGHER RISK DESIGNATION. GIVEN THE CONTINUED INDICATIONS OF POTENTIALLY HEAVY
PRECIPITATION DURING THE NEXT WEEK OR SO, A FLOODING POSSIBLE HAZARD REMAINS
POSTED FOR PORTIONS OF THE FOUR CORNERS. LIKEWISE, THE FLOODING POSSIBLE HAZARD
IS ALSO EXPANDED EASTWARD TO CAPTURE MORE OF THE HEAVY PRECIPITATION RISK AREA,
AND WHERE WEEK-1 PRECIPITATION AMOUNTS ARE FORECAST TO BE IN EXCESS OF 1-2
INCHES OVER PARTS OF NEW MEXICO. THIS REGION IS PRONE TO FLASH FLOODING AND
CAUTION SHOULD BE EXERCISED NEAR CANYONS AND CREEK BEDS.
ACROSS ALASKA, THE PREVIOUSLY FORECAST SLIGHT RISK OF HEAVY PRECIPITATION HAS
TIMED OFF INTO WEEK-1, AND NO HAZARDS ARE POSTED. WHILE ENSEMBLES SHOW MUCH OF
THE MID-LEVEL TROUGHING BECOMING LESS AMPLIFIED OVER THE NORTHERN PACIFIC
DURING THE PERIOD, A REAMPLIFICATION OF THE PATTERN IS POSSIBLE ASSOCIATED WITH
RECURVING TCS FROM THE WESTERN PACIFIC BECOMING ABSORBED INTO THE WESTERLIES
DURING THE PERIOD. ANY MEAN SURFACE LOW DEVELOPMENT AND ACCOMPANYING
PRECIPITATION AND HIGH WIND RISKS WILL CONTINUE TO BE MONITORED IN UPCOMING
OUTLOOKS.
ACROSS THE CENTRAL AND EASTERN PACIFIC, THE NATIONAL HURRICANE CENTER (NHC) IS
CURRENTLY MONITORING NORBERT AND FIFTEEN-E, AND WITH WATCH AREAS CENTERED NEAR
130W AND 105W WITH 20% AND 40% CHANCES FOR DEVELOPMENT, RESPECTIVELY, DURING
THE NEXT WEEK (AS OF 11AM PDT). NORBERT HAS BECOME POST-TROPICAL TODAY, AND
FIFTEEN-E IS FORECAST TO FOLLOW SUIT LATER THIS WEEK, THOUGH THEIR REMNANTS MAY
BRING INCREASED PRECIPITATION AMOUNTS ACROSS HAWAII DURING THE NEXT WEEK.
SHOULD THE TWO WATCH AREAS FORM AND MOVE TOWARDS HAWAII, THIS COULD ALSO POSE
AN ADDITIONAL HEAVY PRECIPITATION RISK TO THE STATE INTO WEEK-2. ANY ADDITIONAL
PRECIPITATION MAY WORSEN ALREADY SATURATED GROUNDS ACROSS PARTS OF HAWAII,
FOLLOWING THE IMPACTS ASSOCIATED WITH TCS LOWELL, MOKE, AND LALA THIS SEASON.
FORECASTER: NICK NOVELLA
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