Tomorrow's rain forecast has the potential to be too much of a good thing, particularly for firefighters.

The National Weather Service has placed much of Southern Oregon and Northern California under a flash flood watch for Thursday afternoon and evening, according to meteorologist Misty Firmin. Though it's difficult to predict where the precipitation will land, Firmin said conditions have the potential to be treacherous as heavy rainfall douses areas ravaged by wildfire.

"With newly burned areas, it doesn't absorb water as efficiently as it should," Firmin said.

Short periods of heavy rainfall and scattered thunderstorms are forecast over the wildfires for a 12-hour period beginning early Thursday afternoon, according to Firmin. Areas could see half an inch in a six-hour period. The Medford area has a chance of rainfall.

"On the higher end of things, we could see over an inch in some places," Firmin said.

Particularly for crews fighting wildfires, mudslides and landslides are a possibility that the weather service is watching closely. Firmin said that the alert is "just a watch," meaning that conditions are currently favorable but have the potential to change. If danger is more certain, the weather service will escalate it to a warning.

"There's a lot of crews working out on these fires," Firmin said. "It's just to raise awareness for them."

Post-fire ash can lead to mass erosion when hit with precipitation, according to Oregon Department of Geology and Mineral Industries spokeswoman Ali Ryan Hansen.

"It's really because the vegetation's reduced," Hansen said. "Also, you loose the root strength in the soils."

 The Oregon Department of Geology and Mineral Industries is advising that travelers avoid burned areas, particularly below steep slopes, canyons and near the mouths of canyons, according to a release issued this afternoon.

"Those recently burned areas are much more susceptible to landslides," Hansen said. "It's definitely something that people need to be aware of."

The map of potentially affected areas spreads as far north as Sutherlin, and well into Humboldt County and west in the Southern Oregon coast from Brookings to Port Orford.

The flash flood watch area covers Jackson County, Josephine County, Curry County, central Douglas County, the eastern Douglas County foothills, the Siskiyou Mountains, the Southern Oregon Cascades and the South Central Oregon Cascades.

— Reach reporter Nick Morgan at 541-776-4471 or nmorgan@mailtribune.com. Follow him on Twitter at @MTCrimeBeat.