Here’s some information of debris flows from the National Weather Service. National Weather Service

Flash flood, debris flow watch in effect through Friday morning

According to a statement from the Lassen County Sheriff’s Office, The National Weather Service in Reno has issued a flash flood watch for a portion of northeastern California, including, Lassen, eastern Plumas and  eastern Sierra counties from Thursday evening through Friday morning.

A short period of heavy rainfall is possible Thursday night and Friday morning in and downstream of the Dixie, Sheep, Walker, and Beckwourth burn scars.

Debris flows, ash flows, rock falls and tree falls are possible with short bursts of heavy rainfall.

For information on how to prepare for possible flooding, go to weather.gov/safety/flood-before.

These are the areas that may be affected by flash floods in the next few hours. National Weather Service

Flood watch

Be Prepared. A flood watch is issued when conditions are favorable for a specific hazardous weather event to occur. A flood watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible.

 

Flash flood warning

Take action. A flash flood warning is issued when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. A flash flood is a sudden violent flood that can take from minutes to hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.

 

What is a debris flow?

According to the National Weather Service, debris flows are fast-moving, deadly landslides. They are powerful mixtures of mud, rocks, boulders, entire trees – and sometimes, homes or vehicles. You’ll often hear “debris flows” called “mudslides” or “mudflows.”

Many people use the terms interchangeably, but to scientists, each is a different kind of landslide and debris flows are the most powerful and dangerous of the three.

 

What causes a debris flow?

Debris flows occur most commonly during intense rain after wildfires. A debris flow doesn’t need a long rain or a saturated slope. It can start on a dry slope after only a few minutes of intense rain.

“Intense” rain means a burst of rain at a fast rate, about half an inch in an hour. With debris flows, the rainfall rate matters more than total rainfall.

 

Why are debris flows so dangerous?

Debris flows are fast and unpredictable. They can travel faster than you can run — and they can catch up to your car. Also, no one can say precisely where a debris flow will start or where it will go. It may begin in a stream channel, then jump out and spread through a neighborhood. A debris flow may happen where others have occurred, or in a place that has never seen one before.