551
FXUS21 KWNC 181801
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 18 2026
SYNOPSIS: BY NEXT WEEKEND, DEVELOPING MID-LEVEL LOW PRESSURE ALONG THE WEST
COAST SUPPORTS THE ONSET OF ENHANCED ONSHORE FLOW, LEADING TO AN INCREASED RISK
OF HEAVY PRECIPITATION AND HIGH ELEVATION SNOWFALL OVER PARTS OF CALIFORNIA AND
OREGON DURING THE WEEK-2 PERIOD. AN ENHANCEMENT OF ATMOSPHERIC MOISTURE IS
ALSO FAVORED OVER THE SOUTHWESTERN U.S., SUPPORTING AN INCREASED RISK OF HEAVY
PRECIPITATION MAINLY OVER THE LOWER FOUR CORNERS. MEANWHILE, RENEWED SURFACE
LOW DEVELOPMENT IS FAVORED OVER THE WESTERN ATLANTIC FOLLOWING A COASTAL LOW
POTENTIALLY IMPACTING THE EASTERN SEABOARD DURING WEEK-1. WHILE THE HEAVIEST
PRECIPITATION AMOUNTS ARE FAVORED OFFSHORE, THE SYNOPTIC PATTERN SUPPORTS
PERIODS OF ELEVATED WIND SPEEDS ACROSS THE MID-ATLANTIC AND SOUTHEAST.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF CENTRAL AND NORTHERN
CALIFORNIA, AND ADJACENT SOUTHERN OREGON, MON-SUN, OCT 26-NOV 1.
SLIGHT RISK OF HIGH ELEVATION HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS,
MON-SUN, OCT 26-NOV 1.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE DESERT SOUTHWEST, GREAT
BASIN, SOUTHERN ROCKIES, AND SOUTHERN HIGH PLAINS, MON-WED, OCT 26-28.
SLIGHT RISK OF HIGH WINDS FOR PORTIONS OF THE MID-ATLANTIC AND THE SOUTHEAST,
MON-THU, OCT 25-29.
DETAILED SUMMARY
FOR WEDNESDAY OCTOBER 21 - SUNDAY OCTOBER 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR MONDAY OCTOBER 26 - SUNDAY NOVEMBER 01: BASED ON THE LATEST ENSEMBLE
GUIDANCE, DYNAMICAL MODEL 500-HPA HEIGHT ANOMALY FORECASTS HAVE COME INTO
BETTER AGREEMENT TODAY IN REGARDS TO THE DEVELOPMENT OF AN AMPLIFIED MID-LEVEL
TROUGH OFF THE WEST COAST AFTER NEXT WEEKEND. A COMPARABLY MORE AMPLIFIED MEAN
SOLUTION IS STILL APPARENT IN THE ECENS ENSEMBLE, WHICH FEATURES A MORE
EXPANSIVE COVERAGE OF NEGATIVE HEIGHT DEPARTURES OVER THE PACIFIC NORTHWEST AND
CALIFORNIA, SUPPORTIVE OF ENHANCED PACIFIC ONSHORE FLOW BY THE START OF THE
PERIOD. IN ADDITION TO THE WEST, A SECONDARY SOURCE OF INCOMING ENHANCED
ATMOSPHERIC MOISTURE IS BEING ADVERTISED IN THE PRECIPITABLE WATER ANOMALY
GUIDANCE ACROSS THE LOWER FOUR CORNERS AND SOUTHERN PLAINS, WHICH APPEARS TO BE
ASSOCIATED WITH ADDITIONAL TROPICAL CYCLONE ACTIVITY IN THE EASTERN PACIFIC.
TAKEN TOGETHER, MUCH OF CONUS WEST OF THE MISSISSIPPI IS PRIMED FOR
ABOVE-NORMAL PRECIPITATION, WITH THE GREATEST RISK OF HAZARDOUS WEATHER IN
PROXIMITY TO THE AMPLIFIED MEAN TROUGH NEARING THE WEST COAST. MEANWHILE ACROSS
THE EASTERN U.S., ENSEMBLES CONTINUE TO ADVERTISE A SECONDARY SURFACE LOW
FORMATION TO THE NORTH OF THE BAHAMAS IN THE WAKE OF A COASTAL LOW INITIALLY
FAVORED DURING WEEK-1. WHILE THE HEAVIEST PRECIPITATION AMOUNTS LOOK TO REMAIN
OFFSHORE IN THE WESTERN ATLANTIC, CONTINUED TROUGHING AND CYCLONIC SURFACE FLOW
IS LIKELY TO BRING A PERIOD OF UNSETTLED WEATHER ACROSS THE LOWER EASTERN
SEABOARD AT LEAST THROUGH EARLY WEEK-2.
WITH ENHANCED ONSHORE FLOW FAVORED ACROSS THE WEST COAST, A SLIGHT RISK OF
HEAVY PRECIPITATION REMAINS POSTED OVER PORTIONS OF CENTRAL AND NORTHERN
CALIFORNIA, AND ADJACENT SOUTHERN OREGON. BASED ON THE CALIBRATED ECENS
PROBABILISTIC EXTREMES TOOL (PET), A MODERATE RISK OF HEAVY PRECIPITATION HAS
BEEN CONSIDERED GIVEN ELEVATED CHANCES (>40%) FOR 3-DAY AMOUNTS EXCEEDING THE
85TH PERCENTILE AND 1 INCH (LOCALLY, AS MUCH AS 20% CHANCES FOR AMOUNTS
EXCEEDING 2 INCHES). HOWEVER, FORECAST CONFIDENCE FOR THIS HIGHER HAZARD
DESIGNATION IS TEMPERED BY THE DRIER SOLUTIONS FOUND IN THE UNCALIBRATED ECMWF,
AS WELL AS THE GEFS AND CANADIAN, WHICH ARE MORE SUPPORTIVE OF A SLIGHT RISK AT
THIS TIME. DUE TO THE DURATION OF ANOMALOUS TROUGHING FAVORED IN THE MODELS,
WITH SOME ENSEMBLE INDICATIONS OF THE MEAN TROUGH RELOADING ACROSS THE WEST
COAST LATER IN OCTOBER (IN CONJUNCTION WITH A RESTRENGTHENING RIDGE CENTER
UPSTREAM OVER THE ALEUTIANS), THE SLIGHT RISK REMAINS VALID FOR ENTIRELY OF
WEEK-2 WHICH IS ALSO SUPPORTED BY THE PETS. THE ENHANCED ONSHORE FLOW FAVORED
ALSO SUPPORTS PERIODS OF ACCUMULATING, AND POTENTIALLY HEAVY SNOWFALL ACROSS
THE HIGHER ELEVATIONS OF THE SIERRA NEVADA MOUNTAINS DURING THE PERIOD.
THEREFORE, A SLIGHT RISK OF HEAVY SNOWFALL REMAINS POSTED FOR ALL OF WEEK-2,
WHERE UNCALIBRATED ECENS TOOLS SHOW INCREASED CHANCES FOR 3-DAY SNOWFALL
AMOUNTS EXCEEDING 6 INCHES WITH BETTER SUPPORT FROM THE GEFS SNOW WATER
EQUIVALENT (SWE) PET DURING WEEK-2. PERIODS OF HIGH WINDS ARE ALSO POSSIBLE AT
THE BASE AND AHEAD OF THE MEAN TROUGH. HOWEVER, IN THE ABSENCE OF STRONG
SURFACE PRESSURE GRADIENTS FAVORED, WEAK SIGNALS IN THE INTEGRATED VAPOR
TRANSPORT (IVT) TOOLS REFLECTIVE OF ATMOSPHERIC RIVER ACTIVITY, AND CONTINUED
LARGE ENSEMBLE SPREAD IN THE GEFS HEIGHT PATTERN, A CORRESPONDING HIGH WIND
RISK IS NOT INCLUDED IN THE UPDATED OUTLOOK FOR THE TIME BEING. THIS POTENTIAL
WILL CONTINUE TO BE REASSESSED IN UPCOMING OUTLOOKS THIS WEEK.
TIED TO THE INFLUX OF ENHANCED MOISTURE ACROSS THE SOUTHWESTERN CONUS, A SLIGHT
RISK OF HEAVY PRECIPITATION IS ALSO ADDED OVER THIS PART OF THE COUNTRY IN THE
UPDATED OUTLOOK. WHILE THE GEFS CONTINUES TO POINT TO A HEAVY PRECIPITATION
THREAT FURTHER EAST LIKELY TIED TO LINGERING FRONTAL ACTIVITY, THIS HAZARD
ADDITION IS PRIMARILY BASED ON THE POTENTIAL FOR SHORTWAVE ENERGY EJECTING
ACROSS THE ROCKIES, WHERE THERE IS ALSO GROWING SUPPORT IN THE ECENS PET FOR
AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 1 INCH, AND AN INCREASE IN THE 6-10
DAY TOTAL PRECIPITATION ANOMALIES FAVORED OVER THE LOWER FOUR CORNERS IN THE
REFORECAST CONSOLIDATION TOOL RELATIVE TO YESTERDAY.
ACROSS THE WESTERN ATLANTIC, ENSEMBLE GUIDANCE HAS SHOWN IMPROVED RESOLUTION IN
REGARDS TO THE DEVELOPMENT OF TWO DISTINGUISHED AREAS OF SURFACE LOW PRESSURE
DURING THE NEXT TWO WEEKS. A COASTAL LOW SITUATED OFF THE MID-ATLANTIC REMAINS
FAVORED TO FORM OFF A FRONTAL BOUNDARY IN THE NEXT DAY OR SO, WHERE THE
NATIONAL HURRICANE CENTER (NHC) DESIGNATES 30% CHANCES (AS OF 2PM EDT) OF THIS
LOW ACQUIRING SUBTROPICAL CHARACTERISTICS DURING THE NEXT WEEK. AS THIS LOW IS
FAVORED TO EVENTUALLY WEAKEN AND BE PUSHED OUT BY REBUILDING HIGH PRESSURE OVER
THE NORTHEAST, ENSEMBLES CONTINUE TO POINT TO A NEW CLUSTER OF DEEPENING LOW
MEMBERS FURTHER SOUTH TO THE NORTH OF BAHAMAS EARLY IN WEEK-2. AS A RESULT, A
RENEWAL OF CYCLONIC SURFACE LOW IS FAVORED AND PRECIPITATION LOOKS TO BECOME
QUITE ENHANCED WITH THE AVAILABILITY OF TROPICAL MOISTURE OFF THE EASTERN
SEABOARD. CONSISTENT WITH PREVIOUS GUIDANCE, THE HIGHEST PRECIPITATION AMOUNTS
IN THE RAW TOOLS ARE FAVORED JUST OFFSHORE AHEAD OF THE TROUGH AXIS, AND PETS
REMAIN UNSUPPORTIVE OF HEAVY PRECIPITATION PROTRUDING ONSHORE. THIS PRECLUDES A
HEAVY PRECIPITATION HAZARD AT THIS TIME, THOUGH THIS POTENTIAL WILL CONTINUE TO
BE CLOSELY MONITORED IN THE UPCOMING HAZARD OUTLOOKS. HOWEVER, GIVEN THE
SYNOPTIC SETUP, A SLIGHT RISK OF HIGH WINDS REMAINS POSTED WHERE THERE
CONTINUES TO BE THE POTENTIAL FOR STRENGTHENING SURFACE PRESSURE GRADIENTS TIED
TO THE TROUGHING ALOFT. THE SLIGHT RISK REMAINS VALID THROUGH OCT 29 BEFORE
MUCH OF THE TROUGHING ALOFT DEAMPLIFIES.
OVER ALASKA, 500-HPA TROUGHING AND AN ACCOMPANYING SURFACE LOW IS FAVORED TO
LIFT OUT OVER THE BERING STRAIT, WITH RISING MID-LEVEL HEIGHTS FAVORED OVER THE
ALEUTIANS AND SOUTHERN MAINLAND NEXT WEEKEND. THIS PATTERN CHANGE LOOKS TO
BRING DRIER CONDITIONS TO PARTS OF THE SOUTHERN MAINLAND AND THE SOUTHEAST,
WHILE SHIFTING THE ENHANCED PRECIPITATION AND POTENTIAL FOR ELEVATED WIND
SPEEDS FURTHER NORTH INTO MORE OF THE MAINLAND. WHILE BOTH THE PRECIPITATION
AND WIND BASED PETS REFLECT THIS NORTHWARD SHIFT, AS WELL AS AN UPTICK IN
SIGNALS IN PERCENTILE SPACE COMPARED TO YESTERDAY, THERE REMAINS LOW CHANCES
THAT PRECIPITATION AMOUNTS AND WIND SPEEDS EXCEED SEASONAL HAZARD THRESHOLDS
FOR ALASKA, RESULTING IN NO HAZARDS BEING POSTED FOR THE STATE.
FORECASTER: NICK NOVELLA
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