January 22, 2018 – Pacific storm moves through bringing mainly light precipitation. A stronger system impacts the area mid-week into Friday bringing moderate to heavy rain, mountain snow and gusty wind.
Discussion
The front has continued to work its way slowly southward across interior NorCal overnight. Precip picked up as a weak wave moved onshore, and some light to moderate snow will continue across the northern Sierra into the morning with additional snowfall accumulations up to 4 inches leading to chain requirements along I-80, so a winter weather advisory has been posted.
Further north, profiler data indicates snow levels have risen above 3K feet across Shasta County and traffic cameras show wet road surfaces along Interstate 5 north of Redding, so the winter weather advisory for that area has been cancelled.
Precip along the front is forecast to taper dramatically by afternoon as upstream ridging moves in. However, moisture will remain trapped below the subsidence inversion so clouds will be stubborn, persistent and slow to clear for much of the region.
After a break, a stronger Pacific frontal system spreads inland over far NW CA Tuesday night then across all of Interior NorCal Wednesday. Breezy to windy conditions develop ahead of the front Wednesday. Models currently show more significant QPF with this storm. Snow levels attm initially look to be around 5000 to 6000 feet Wednesday morning, but lower to 2500 to 3500 feet Wednesday night into Thursday in post-frontal colder AMS. Showery weather persists Thursday.
Extended discussion (Friday through Monday)
Area of high pressure will bring mostly dry conditions Friday for northern California, although a few lingering showers across the Cascades and extreme northern Sacramento Valley are possible. The next low pressure system to make landfall will affect the Pacific northwest and the Cascade/Coastal mountains of the interior, which will bring another round of precipitation chances for Saturday. High pressure returns for Sunday before the next weather making system approaches for early next week, mainly affecting the northern valley and mountains.