Heavy rain could cause debris slides in Nevada County’s burn areas | TheUnion.com

Heavy rain could cause debris slides in Nevada County’s burn areas

The first big rainstorm of the season has hit Nevada County, sparking fears of debris flows in wildfire burn areas.

This major early-season winter storm will impact Northern California through today and into Friday morning, National Weather Service forecasters said.

A band of heavier precipitation was forecast to develop Wednesday night into this morning, resulting in ponding of water on roads and possibly minor rock and debris flows over recent burn scars.

"Forecasts will never be precise, but that being said, the latest forecast is in the neighborhood of 3-5 inches through early Friday morning," forecaster Tom Dang said late Wednesday afternoon. "The heaviest rain will come late (Wednesday) evening."

There was only light rain through most of Wednesday, with 0.18 inches recorded at Nevada County Airport as of just before 5 p.m., 0.33 inches in Cedar Ridge over 24 hours.

The heavy rain bands predicted do cause some concern for debris flow, Dang said.

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Normally, vegetation absorbs rainfall, but wildfire leaves the ground charred, barren and unable to absorb water. Rain over recently burned areas can cause debris to slide down slopes; debris can then clog culverts and drains, causing flooding.

"The tricky issue is that the fires occurred fairly recently, and we haven't had time to analyze how susceptible they are to debris flow," Dang said.

The weather service is monitoring burn scar areas, he said, adding that only minor debris flows are being predicted.

A winter storm warning is in effect through today above 6,000 feet with periods of moderate to heavy snow along with strong gusty winds. The heaviest snow is expected through Thursday evening. Motorists planning travel into the mountains during this time frame should be prepared for hazardous winter driving conditions.

A flood advisory also has been issued through 2:45 p.m., with the band of rain forecast to move slowly south of Interstate 80 early this morning. Rainfall rates may exceed a half inch to nearly one per hour in the foothills and higher elevations of the Sierra.

Rain is predicted before 10 a.m., turning to showers, heavy at times. Tonight showers are forecast, mainly before 10 p.m. Friday is expected to be mostly sunny, with rain returning Sunday.

Contact reporter Liz Kellar at 530-477-4236 or by email at lkellar@theunion.com.