UPDATED: Strongest September Storm on Record Strikes Washington and Oregon

UPDATED: Strongest September Storm on Record Strikes Washington and Oregon

A windy and wet storm has pounded the western portions of Washington and Oregon since Friday depositing the heaviest September rainfalls ever observed in the region and bringing wind gusts of 85 mph to the coast. A tornado touched down in Frederickson near Tacoma, Washington. OCTOBER 1st UPDATE: I have updated the precipitation totals for the storm and the month of September.

A massive plume of moisture (fed by a decaying Typhoon Pabuk in the western Pacific) has flowed into the Pacific Northwest coast since last Friday (September 27) and become entrained into a powerful surface low-pressure system (with a central pressure of at least 979 mb/28.90”).



Water vapor image from last Saturday (September 28th) illustrates the long fetch of moisture slamming into the Pacific Coast. Image from Dept. of Atmospheric Sciences, Univ. of Washington, Seattle.

The center of the low pushed inland over Canada’s Vancouver Island on Sunday September 29th bringing the heaviest rain and strongest winds ever measured for the month of September to coastal Washington and Oregon. In Oregon a peak wind gust of 85 mph was recorded on Mary’s Peak (elev. 4137’) at 8:25 pm. PT on Sunday evening and a wind gust of 81 mph was reported in Washington at a site 4 miles north-northeast of Naselle at 6:50 p.m. the same night.



High winds toppled this tree onto a mobile home in Hillsboro, Oregon (a western suburb of Portland) on Saturday afternoon. Photo from Hillsboro Fire and Rescue.

More remarkable than the winds, however, has been the phenomenal early-season rainfall. Seattle experienced its wettest September day on record Saturday (September 28th) when 1.71” was measured at Sea-Tac Airport (previous record was 1.65” on September 22, 1978). The same occurred at Olympia, Washington with 2.93” (old record 1.67” on September 17, 2010) and Astoria, Oregon with 3.16” (former record 2.67” on September 16, 1997). But these were for just one day of the three-day storm. As of 8 a.m. Monday morning (September 30th) Swift Creek, Oregon (in the Mt. St. Helen’s area) has picked up 15.30” of precipitation since Friday morning. Seattle’s storm total (for Sept. 27-30) has been 2.90” bringing the September total to 6.17”, their all-time wettest such on record besting the 5.95” set in 1978. Olympia also surpassed its monthly record with 9.36” surpassing the former figure of 7.59” also set in 1978.

In Oregon, virtually every major site in the western third of the state has also already broken their monthly precipitation September record. Here is a list published by the NWS for totals as of 8 a.m. PT September 30:



UPDATE OCTOBER 1:

The final precipitation totals for September for the locations listed above are the following:

Astoria: 10.70"
Eugene: 7.08"
Portland Airport: 5.62"
Salem: 7.05"
Hillsboro: 6.27"
McMinnville: 6.19"
Vancouver, WA: 5.24"

On Monday morning post-frontal instability brought thunderstorms to the Seattle area and a confirmed tornado touchdown (at 7:20 am. PT) in Frederickson near Puyallup (about 45 miles south of Seattle). The tornado (rated EF-0) struck a Boeing manufacturing plant but caused only minor damage. This was the first confirmed tornado in the Seattle area since May 27, 2011 when a week EF-0 touched down near Napavine in Lewis County.