Flood watch issued for 3 counties hit by NorCal wildfires

The National Weather Service has issued a warning of possible flash flooding in three counties in Northern California in advance of a rainstorm that’s expected to arrive late Wednesday in areas where devastating wildfires have recently burned.

Forecasters predict the second in a series of three storm systems this week could drop more than an inch of rain on the Camp fire burn area in Butte County; the Carr, Delta and Hirz fires burn areas in Shasta County; and the Mendocino Complex fire scar in Lake County.

Because the rain will be spread out over more than 12 hours from Wednesday through Thursday morning, forecasters are not especially concerned about deadly mudslides in the burn areas. However, flash flooding is possible if a heavy rain cell forms directly above one of the burn areas, said Mike Smith, a meteorologist with the National Weather Service in Sacramento.

The soil in areas recently burned cannot absorb significant amounts of rainwater, so excessive precipitation can lead to fast-moving flows containing mud, debris, and even trees and boulders. When rain comes over time, it can be gradually absorbed or dispersed, but when areas see rapid runoff, that’s when entire hillsides can come down, resulting in destructive mudslides. The devastation can be deadly and often comes without warning.

Smith said the chances of ash and debris flows are more likely in Butte County because it’s freshly burned, but the other two counties should also be on alert.

“Our concern is if we get a heavy shower or if a thundershower goes right over the burn area,” Smith said. “People should be prepared, but a large-scale mudslide isn’t something we’re especially concerned about right now.”

Smith said there is a greater chance the areas could see fast-moving floods because vegetation that typically would slow water was charred during the fires.

The Butte County Emergency Operations Center has prepared for the rain by clearing drainage culverts of debris, said Matt Gates, public information officer for the Paradise Police Department.

The California Conservation Corps also has been working on erosion-control measures for mountain slopes filled with fire-damaged pine and chaparral.

“Ash doesn’t absorb water, which complicates things,” Gates said.

The National Weather Service said people in burn

areas should prepare to leave quickly if heavy rain begins, noting in its alert that “this could quickly become a dangerous situation.”

Butte County officials said residents should not wait for a flash flood warning because hazards could develop before an alert is issued.

“If you are in the impacted area or are located near a waterway

downstream from the impacted area, you should be prepared to immediately evacuate to high ground in the event of heavy rainfall, an evacuation notice, or any evidence of soil instability in your area,” county officials wrote in a news release.