Thunderstorms in Oregon forecast could spark new wildfires, trigger flash floods

Lightning sparked numerous wildfires on the Umpqua and Rogue River-Siskiyou (pictured) national forests in August.  Some of those fires continue to burn as September arrives. (USDA Forest Service photo)

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EUGENE, Ore. - A change in the weather could help ease the smoke choking Oregon - and usher in a new round of dangers.

Long story short: Thunderstorms in the forecast could spark new fires - or dump enough rain on burn scars to trigger flash floods.


The National Weather Service in Portland issued a Red Flag Warning for abundant lightning, in effect from 3 p.m. this afternoon to 11 p.m. Thursday.

The forecast calls for thunderstroms with Lightning Activity Level 3, on a scale of 1 to 6. That means the storms could bring light to moderate rain - and up to 60 lightning strikes per hour.

"Thunderstorms will generally be moving northwestward fast enough to prevent widespread wetting rains," forecasters explained.

The storms appear likely starting late Wednesday afternoon through Thursday.

"The focus late this afternoon/evening and tonight will likely be south of a line extending between Mount Jefferson and Tillamook," forecasters explained in the Red Flag Warning. "The focus should shift north of a line extending between the Three Sisters and Tillamook for Thursday."

The potential danger?

"Frequent lightning and critically dry fuels may result in numerous fire starts," forecasters said.

Firefighters are already in short supply, with the nation's firefighting resources and equipment committed to existing fires - and fire bosses asking for more to fight blazes across the West.

Oregon has mobilized over 650 National Guard troops to help fight fires, and 200 active duty soldiers from Washington are expected to deploy to Oregon next week.

The change in the weather is a mixed bag for wildfires already burning in Oregon.

"Higher humidity and cloud cover should moderate fire activity," managers of the fires burning on the Willamette National Forest said in a statement Wednesday afternoon, "but the potential for strong outflow winds associated with thunderstorms could increase fire activity."

Flash Flood Risk

"Heavy rain with thunderstorms could produce flash flooding on burn scars," the National Weather Service in Medford warns.

"Heavy rain can trigger landslides," said Bill Burns, engineering geologist at the Oregon Department of Geology and Mineral Industries. "With storms in the forecast, it's important to be aware of the landslide hazard and avoid burned areas."

The warning is in effect for most of Douglas, Curry, Josephine and Jackson counties in Oregon, as well as parts of northern California.

"An unusually moist air mass over the region will combine with thunderstorms to produce the threat of heavy rainfall. If these heavy rains fall on burn scar areas, dangerous runoff could result," forecasts said in issuing a Flash Flood Watch. "Flash flooding, debris flows, and/or mudslides may occur in and down drainage from recent wildfire burn scars."

The state geology department said people, buildings and roads located at the base of steep canyons and near the mouths of canyons are most at serious.

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