The first in a series of storms is expected to move into Northern California tonight and continue through the weekend, bringing rain to the Sacramento area and the potential for some of the lowest snow levels so far this season.
But the storm is moving more slowly than expected, meaning clear, calm conditions could result in frost and black ice on roadways early this morning, said Jim Mathews, a meteorologist with the National Weather Service in Sacramento.
Icy conditions on Interstate 5 north of Yreka may have contributed to collisions involving about 60 vehicles Tuesday night. I-5 was closed in both directions for nearly 12 hours.
The Associated Press reported eight people were taken to hospitals. According to the California Highway Patrol, six were treated and released and two were admitted with serious injuries.
Rain is expected to start falling around Redding and Red Bluff this afternoon, moving into the Sacramento area by evening and continuing into Friday. Another storm is due to move through Saturday and Sunday.
Mathews said the storms likely will drop about an inch of rain in Sacramento, and perhaps up to 2 inches around Folsom and the eastern part of the county.
Highs in the low 50s and overnight lows in the low 40s are forecast for the Sacramento area, about average for this time of year.
The storms may complicate holiday travel plans, with the potential for several inches of slushy snow around Redding and several feet over the mountains, including I-5 north of Shasta Lake and I-80 over Donner Pass, according to the National Weather Service. Shasta County could see snow as low as the 500-foot elevation.
In the Mother Lode, snow levels could drop as low as 2,000 feet, Mathews said. Blue Canyon on Interstate 80 is expected to receive 8 to 9 inches Friday and more than a foot of snow Friday night.
The rain and snow will taper off Monday, Mathews said, and the forecast for Christmas Day in the Sacramento region is partly cloudy with highs in the low 50s.