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FXUS21 KWNC 201923
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 20 2025
SYNOPSIS: THE FIRST HALF OF THE WEEK-2 FORECAST PERIOD IS EXPECTED TO FEATURE A
SIGNIFICANT DECREASE IN STORM ACTIVITY ACROSS THE WEST COAST. MODELS ARE
FORECASTING THE DEVELOPMENT OF A STRONG STORM SYSTEM OVER THE GULF OF ALASKA,
WHICH MAY RETURN WEATHER-RELATED HAZARDS AND IMPACTS TO PARTS OF THE WEST COAST
DURING THE LATTER HALF OF WEEK-2, AS WELL AS SOUTHCENTRAL AND SOUTHEASTERN
ALASKA. EAST OF THE ROCKIES, LOW PRESSURE ALOFT AND AT THE SURFACE IS FORECAST
TO BRING HAZARDOUS PRECIPITATION AND WIND TO MANY AREAS.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF NORTHERN CALIFORNIA AND THE
PACIFIC NORTHWEST, TUE-MON, OCT 28-NOV 3.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE LOWER AND MIDDLE MISSISSIPPI VALLEY,
THE OHIO AND TENNESSEE VALLEYS, PARTS OF THE SOUTHEAST, THE APPALACHIANS,
MID-ATLANTIC, AND NORTHEAST, TUE-SAT, OCT 28-NOV 1.
SLIGHT RISK OF HEAVY SNOW FOR THE CASCADE MOUNTAINS, TUE-WED, OCT 28-29, AND
SUN-MON, NOV 2-3.
SLIGHT RISK OF HEAVY SNOW FOR PORTIONS OF THE NORTHERN INTERMOUNTAIN REGION,
AND NORTHERN AND CENTRAL ROCKIES, TUE, OCT 28.
MODERATE RISK OF HIGH WINDS FOR THE PACIFIC NORTHWEST, TUE-SUN, OCT 28-NOV 2.
MODERATE RISK OF HIGH WINDS FOR THE NORTHERN AND CENTRAL PLAINS, AND
NEIGHBORING PORTIONS OF THE MISSISSIPPI VALLEY, TUE-THU, OCT 28-30.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE NORTHERN, CENTRAL, AND EASTERN CONUS,
TUE-SUN, OCT 28-NOV 2.
FLOODING POSSIBLE ACROSS PARTS OF THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA.
DETAILED SUMMARY
FOR THURSDAY OCTOBER 23 - MONDAY OCTOBER 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY OCTOBER 28 - MONDAY NOVEMBER 03: WITH THE BULK OF THE
WEATHER-RELATED HAZARDS ASSOCIATED WITH AN ATMOSPHERIC RIVER (AR) NOW PREDICTED
INSIDE THE WEEK-1 TIME FRAME, THE WEST COAST IS EXPECTED TO SEE A SIGNIFICANT
DECREASE IN STORM ACTIVITY EARLY IN WEEK-2. DURING THE WEEK-2 HAZARDS PERIOD,
THERE IS A SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST AND
MUCH OF NORTHERN CALIFORNIA, WITH CONDITIONS EXPECTED TO EASE SUBSTANTIALLY
OVER CALIFORNIA AS EARLY AS DAY 9 (OCT 29). WITH THE PRIMARY IMPACTS OF THE AR
NOW PAST, THE PACIFIC JET IS PREDICTED TO MIGRATE NORTHWARD ACROSS THE PACIFIC
NORTHWEST AS 500-HPA HEIGHTS RISE ACROSS THE SOUTHWESTERN CONUS. SLIGHT RISKS
OF HIGH ELEVATION HEAVY SNOWFALL ARE POSTED ACROSS THE CASCADE MOUNTAINS (OCT
28-29, WITH A RENEWAL OF POTENTIALLY HEAVY SNOWFALL TOWARDS THE END OF WEEK-2,
NOV 2-3). PACIFIC MOISTURE STREAMING INLAND IS ALSO FORECAST TO WARRANT A
SLIGHT RISK OF HIGH ELEVATION HEAVY SNOWFALL ACROSS PARTS OF THE NORTHERN
INTERMOUNTAIN REGION, AND THE NORTHERN AND CENTRAL ROCKIES. THE CALIBRATED
PROBABILISTIC EXTREMES TOOLS (PETS) FROM THE ECENS AND GEFS, AS WELL AS DIRECT
DYNAMICAL MODEL OUTPUT FROM THESE MODELS, GENERALLY FAVOR PRECIPITATION AMOUNTS
EXCEEDING THE 85TH HISTORICAL PERCENTILE, AND 1.0-1.5 INCHES OF PRECIPITATION.
FOR MANY AREAS WEST OF THE ROCKIES, PET GUIDANCE FOR HIGH WINDS (ESPECIALLY THE
MORE BULLISH ECENS) AND UNCALIBRATED ECENS DYNAMICAL MODEL GUIDANCE SUPPORT
SLIGHT AND MODERATE RISKS FOR WIND SPEEDS EXCEEDING THE 85TH HISTORICAL
PERCENTILE AND GENERALLY RANGING BETWEEN 25-35 MPH, WITH HIGHER GUSTS. THE
MODERATE RISK AREA IS FOCUSED ON THE PACIFIC NORTHWEST AND IS VALID THROUGH NOV
2. A SLIGHT RISK OF HIGH WINDS (>40 MPH) IS ALSO SUPPORTED FOR SOUTH-CENTRAL
AND SOUTHEASTERN ALASKA FOR THE SECOND HALF OF WEEK-2, BASED ON THE SAME WIND
TOOLS (AND TO A LESSER DEGREE THE GEFS PET), AND THE PREDICTED DEVELOPMENT OF A
STRONG CYCLONIC SYSTEM OVER THE GULF OF ALASKA.
OVER THE BERING SEA, A RELOADING MID-LEVEL TROUGH AND ACCOMPANYING STRONG
SURFACE CYCLONE ARE FORECAST TO MOVE ACROSS THE GULF OF ALASKA, WITH THE
POTENTIAL FOR A SECOND AR EVENT ACROSS THE U.S. PACIFIC NORTHWEST, NORTHERN AND
CENTRAL CALIFORNIA, AND THE SOUTH-CENTRAL AND SOUTHEASTERN COASTS OF ALASKA
DURING THE SECOND HALF OF WEEK-2. IF THE ECENS, GEFS, AND CMCE DYNAMICAL MODELS
PREDICT THIS SAME SCENARIO TOMORROW, MODERATE (OR EVEN HIGH) RISKS OF HEAVY
PRECIPITATION AND HEAVY SNOW MAY BE REINSTATED ACROSS THE WEST COAST STATES
EITHER TOMORROW OR WEDNESDAY. PREDICTED SNOWFALL AMOUNTS MAY REACH OR EXCEED 6
INCHES WITHIN A 24-HOUR PERIOD IN THE HIGHER ELEVATIONS OF THE WEST.
EAST OF THE ROCKIES, AN AMPLIFIED MID-LEVEL TROUGH AND AN ACCOMPANYING SURFACE
LOW PRESSURE SYSTEM ARE FORECAST TO TRACK FROM THE CENTRAL CONUS TO THE EASTERN
SEABOARD DURING WEEK-2. THE MAIN HAZARDS PREDICTED TO ACCOMPANY THESE FEATURES
ARE HEAVY PRECIPITATION AND HIGH WINDS. FOR PRECIPITATION, THE PETS (ESPECIALLY
THE MORE BULLISH ECENS) FAVOR A SLIGHT RISK OF HEAVY PRECIPITATION (AT LEAST
1-INCH OVER A 3-DAY PERIOD) ACROSS THE LOWER AND MIDDLE MISSISSIPPI VALLEY, THE
OHIO AND TENNESSEE VALLEYS, PARTS OF THE SOUTHEAST, MID-ATLANTIC, AND
NORTHEAST, OCT 28-NOV 1. PRECIPITATION IS ALSO FORECAST ACROSS THE UPPER
MIDWEST AND UPPER GREAT LAKES REGION, BUT SUBHAZARDOUS AMOUNTS (0.50 TO
0.75-INCH) ARE PREDICTED. ONE AREA THAT MAY NEED A MODERATE RISK OF HEAVY
PRECIPITATION TOMORROW IS THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS (ON THE
SOUTHERN PERIPHERY OF A DEEP MID-LEVEL TROUGH), BUT THIS POTENTIAL WILL BE
REASSESSED THEN. REGARDING WIND HAZARDS, THERE IS A SLIGHT RISK OF HIGH WINDS
POSTED FOR MOST AREAS EAST OF THE CONTINENTAL DIVIDE FOR MOST OF WEEK-2 (AREAS
WEST OF THE DIVIDE WERE DISCUSSED EARLIER). A MODERATE RISK OF HIGH WINDS IS
POSTED FOR THE NORTHERN AND CENTRAL PLAINS, AND ADJACENT PORTIONS OF THE
MISSISSIPPI VALLEY, OCT 28-30. THESE HAZARDS ARE RELATED TO THE PREDICTED
PASSAGE OF AN AMPLIFIED MID-LEVEL TROUGH AND ACCOMPANYING SURFACE CYCLONE.
THE NATIONAL HURRICANE CENTER (NHC) INDICATES A 90 PERCENT CHANCE OF A TROPICAL
CYCLONE FORMING IN THE CARIBBEAN DURING WEEK-1. SOME OF THIS TROPICAL MOISTURE
MAY GET PULLED UP IN ADVANCE OF THE APPROACHING MID-LEVEL TROUGH OVER THE
CENTRAL AND EASTERN CONUS, BRINGING RAIN TO SOUTHERN FLORIDA. HOWEVER, THERE IS
TOO MUCH UNCERTAINTY CONCERNING THE DETAILS OF THIS SCENARIO AND ALSO THE
RESULTING PRECIPITATION AMOUNTS.
FOR THE TIME BEING, A FLOOD RISK REMAINS POSTED FOR THE PACIFIC NORTHWEST AND
NORTHWESTERN CALIFORNIA. THIS RISK WILL BE REASSESSED TOMORROW, AND WILL DEPEND
LARGELY ON THE LIKELIHOOD OF A STRONG CYCLONIC SYSTEM DEVELOPING OVER THE GULF
OF ALASKA DURING THE FIRST HALF OF WEEK-2.
FORECASTER: ANTHONY ARTUSA
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