Wildfire — North Oregon Cascades, Oregon

2020-09-07 to 2020-09-30 · North Oregon Cascades, Oregon

Event narrative

The Lionshead fire crossed into the NWS Portland CWA around 2330PDT on September 7, 2020. The fire spread into eastern Marion county, OR and small parts of Linn & Clackamas counties and grew to approximately 110,000 acres before merging with the Beachie Creek fire. Destroyed were 264 residences, 14 non-residential commercial properties, and 2 other structures. An additional 70 structures were damaged. Towns affected were Detroit, Idanha, and Breitenbush Springs resort. There were 147 people evacuated, 10 first responders injured and no fatalities. The fire was started by lightning and was declared contained on Nov 16, 2020.

Wider weather episode

After a period of upper level ridging brought a return to above normal temperatures in early September, very strong easterly downslope and offshore winds off the Cascades and Coastal Ranges occurred. Winds increased rapidly during the afternoon and evening of September 7 with the passage of an unseasonably strong backdoor cold front, and persisted through much of the following day. This resulted in extremely critical fire weather conditions when the strong winds combined with extremely low relative humidity and exceptionally dry existing fuel conditions. The result was explosive growth of ongoing wildfires, and the new start and explosive spread of numerous new wildfires. Widespread wind gusts from 50-70 mph were common on ridge tops and numerous other in exposed areas, including portions of the greater Portland metro area, the Willamette Valley, and areas of the Oregon coast. Strong winds caused widespread damage to trees, and downed numerous power lines across the region, which started at least 13 additional wildfires. Large portions of the cities of Detroit, Mehama, and Gates were destroyed, and significant portions of Idanha, Mill City, and Lyons also burned. Resultant large wildfires included these named incidents - In Oregon: Beachie Creek, Chehalem Mountain/Bald Peak, Riverside, and Lionshead, and in Washington: Big Hollow. Rapidly spreading wildfires resulted in multiple fatalities, hundreds of displaced persons for many weeks, and billions of dollars in damage.

Source: NOAA Storm Events Database, event_id 931968. Narrative written by the NWS forecast office that issued the report.