We're dealing with some patchy fog across northern California this morning, and then we'll see increasing clouds and showers on the way through the day. Showers will start out along the northwest corner of our region early today, and will spread across the valley and into the Sierra through this afternoon. Heavier rain and snow are expected to track through northern California tonight. Winter Weather Advisories have been issued for areas of the Sierra, Modoc County, and Siskiyou County down to 5000'. The first advisory will go into effect from 4pm this afternoon and last through 7am Thursday in Modoc and Siskiyou Counties. The eastern slopes of the Sierra will be under the advisory from 7pm tonight through 10am Thursday, and the western slopes will be under the advisory from 9pm tonight through 10am Thursday. Snow levels will dip to as low as 3500' as this wet system moves through, and we could be dealing with up to a foot of snow down to 5000'. Our higher peaks could see 18 inches of snow on the way. Snow levels will mostly start out between 5000' to 6000', but will drop tonight. Temperatures are starting out in the 30's in the valley and foothills, and in the 20's to 30's in the mountains this morning. We'll have winds out of the southeast to around 15mph this afternoon, with gusts up to around 30mph in the Sierra. High temperatures will end up in the low to mid 50's in the valley, in the mid 40's to low 50's in the foothills, and in the low 40's to low 50's in the mountains this afternoon.
Travel impacts will be very likely for mountain areas as we start out on Thursday morning, and roads will be slick from the rain in the valley and foothills. Current projections keep snowfall rates under a half an inch an hour, but there will still be potential for mudslides and debris flows in your forecast. Some flooding will be possible late Wednesday night through early in the day on Thursday. We'll mostly dry out by mid day on Thursday, but some showers will be lingering in the Sierra through the afternoon. Fog will be possible over the next several mornings in the valley and foothills. Temperatures will be warmer for the start of your Thursday, and a little warmer for the afternoon. Valley areas can expect lows in the low to mid 40's and highs in the mid to high 50's. Foothill areas will mostly start out in the 40's and will end up in the upper 40's to lower 50's, and mountain areas will start out in the 20's to 30's, and end up in the 40's.
We'll be dry with some clearing in the skies on Friday. Temperatures will dip back into the 30's in the valley and most foothill areas on Friday morning, while mountain aresa dip into the teens to 20's. High temperatures will end up in the mid to high 50's in the valley, and in the 40's to mid 50's in the foothills and the mountains. The temperature trend looks to stay similar through your weekend and we'll see fluctuating clouds. Some valley areas may briefly top out in the lower 60's over the weekend. A weak wet system will bring the potential for mostly mountain showers back into our forecast from late Sunday through Monday. Models are hinting at a slight chance for showers in mostly mountain areas early next week, but confidence is low on more wet weather moving through. We'll get a much better idea of what kind of shower activity to expect on Christmas week as we head through this weekend. Make sure you stay safe on the roads, as major travel impacts will be possible from tonight through at least early tomorrow. Mountain roads will likely be impacted through Thursday evening.