A series of winter storms will bring multiple rounds of valley rain, mountain snow, and gusty winds each day Tuesday afternoon through the weekend, likely continuing into next week. Little break in precipitation is expected, which will likely cause significant holiday travel impacts, especially over the mountains later this week with periods of moderate to heavy snow.
Discussion
Short term concern is with potential for fog development. Some patches of dense fog this morning in the valley around Sacramento and areas northward through Oroville. Low clouds are once again slowing development but winds remain light. Will monitor if the fog can become more widespread this morning but for now patchy dense seems to be what will likely occur.
The focus will shift this afternoon to an incoming storm. The system will spread rain/snow along the coastal range this afternoon and then spread to the western slopes tonight. Dry air in place with low dewpoints will likely bring snow down to lower levels, possibly down to 3500 feet over parts of Shasta County and 4500 feet for the western slopes of the Sierra Nevada.
The initial rain/snow later today and tonight is expected to be light but increase in intensity Wednesday night into Thursday for the western slopes. Further north amounts look to remain lighter and snow levels high enough Wednesday night that I have kept the advisory through Wednesday night for the coastal range and over Shasta County.
Heavier rain and snow looks to focus over western slopes starting around I-80 then spreading northward overnight and into Thursday morning into Plumas County.
Some lowering of the snow levels is expected over the north on Thursday but the colder air is not expected until Thursday night and Friday morning over the entire area when snow levels should drop to 2500 to 3500 feet.
Snowfall does taper in intensity and becomes much lighter on Friday so amounts at the lower elevations are not expected to be great at this time.
Breezy to locally windy conditions are expected later Wednesday night into Thursday with the stronger wave moving over the area. Winds generally 15 to 25 mph with gusts to 35 mph for the valley but locally higher winds are possible. Mountains may see gusts 50 to 70 mph over the ridgetops during this time period.
Extended Discussion (Saturday through Tuesday)
A trough will remain over the west coast with shortwaves developing along the upper backside of the trough and rotating into the region. Snow levels look to remain low between 2500 to 3500 feet for most of this time period but may lower to 1500 to 2500 feet at times through Tuesday.
There will be two main systems with the first moving in late Friday night and Saturday and then taper on Sunday. The second will move over the region on Tuesday.
Showers will remain between the systems, especially over the mountains. Each of these main systems will have the potential to bring several feet of snow over the western slopes. Rainfall amounts for the valley look low enough that there are no flooding concerns at this time.