The wettest of all two storm systems of the week in the Sacramento Valley and Sierra arrived Friday, with the main event expected to take place Friday evening.

This storm taps into an atmospheric river, a narrow cloud of subtropical moisture that produces intermittent heavy rain and snow.

There will be occasional showers Friday afternoon, but the heaviest precipitation is expected Friday night into Saturday afternoon. Heavy rain is possible in the valley and foothills. Gusty winds will accompany the main front advancing with gusts up to 50-55 mph in some parts of the Valley and up to 55 mph in the Sierra.

The gusty winds and heavy rains then penetrate the Sierra and turn into snow. This results in difficult to impossible travel conditions above 5,000 feet.

A winter storm warning is in effect until 4 p.m. Saturday, with heavy snow and wind gusts up to 55 mph.

A strong wind warning is in effect Bay Area to 7 a.m. Saturday. Some North Bay counties are under a flood advisory until 4 p.m. Sunday, and the Sacramento Valley is under a wind advisory until midday Saturday.

If you had outdoor plans on Saturday, it’s best to find an indoor solution as it lasts from Saturday until Sunday morning.

Power outages are possible. More than 15,500 Sacramento Municipal Utility District customers briefly lost power near Sacramento Executive Airport on Friday evening.

Be prepared for winter travel if your weekend plans take you over Sierra passes. Chain controls, delays and closures are possible.

Caltrans shut down I-80 westbound in Truckee Friday night due to multiple spinouts. However, it reopened with chain checks from Truckee to Baxter. Eastbound was still open, but with chain controls from Cisco to Truckee.

Showers will begin to taper off Sunday morning, leaving Sunday afternoon dry across the valley and most foothill towns. A few lingering snow showers are possible across the Sierra after sunrise.

The rest of the weekend will stay mostly dry before we look at another fast-moving storm system on Monday.

Storm totals

The two squalls this week will help us meet our snowpack and water goals by next year.

Some spots in the northern Sacramento Valley saw 1 to 2 inches of rain, while closer to downtown Sacramento up to 1.5 inches of rain is expected. The UC Berkeley Central Sierra Snow Lab reported 12.2 inches of snow since Wednesday and nearly 9.5 inches of snow since Thursday morning.

12/13/24 8:45 AM Update:
24 Hours ❄️ – 9.4″ (24 cm)
48 hours ❄️ – 12.2″ (31 cm)

There are thunderstorms, but heavier snowfall is expected during the afternoon/evening. Heavy snowfall is expected to continue into tomorrow, with additional accumulations of 60 to 90 cm.#Snow #CAwx #CAwater pic.twitter.com/vCwlqZBzu2

— UC Berkeley Central Sierra Snow Lab (@UCB_CSSL) December 13, 2024

Through Sunday, 1 to 3 feet of additional snow is expected at elevations above 5,000 feet, with more than 40 inches around higher peaks.

Storm probabilities next week

Another storm system threatens to emerge early next week. Early models show this starting as early as Monday morning and leading to scattered showers and more snow across the Sierra by Monday night.

This storm will be weaker than the weekend one and fast-moving like Thursday’s storm. Tuesday and Wednesday are expected to be dry, with partly cloudy skies and high temperatures in the upper 50s through the afternoon.

After Monday, our pattern dries out again by midweek, but another storm or two could be possible toward the following weekend.

The timing and strength of Monday’s storm is expected to change over the next few days. So be sure to stick with the CBS Sacramento First Alert Weather team as we work out the details.