SAN FRANCISCO (CBS SF) — A large decaying cyclone off the West Coast triggered showers in the San Francisco Bay Area and snow flurries in the Sierra early Wednesday, the first of several storm fronts predicted for the region stretching through the Christmas holiday weekend.

The National Weather Service said Northern California was in the midst of an active weather pattern, a welcomed relief for a region that has been in the grip of severe drought conditions for much of the year.

READ MORE: UPDATE: Crews Make Progress in Big Sur Firefight; Containment at 35 Percent

“The western U.S. is entering a period of increasingly unsettled weather as moisture from a large decaying cyclone off the West Coast is forecast to push onshore,” the NWS said in its national outlook. “The precipitation currently moving into Northern California is only a preview of what is to come as another low pressure system near the west coast of Canada is forecast to track toward the Pacific Northwest during the next couple of days.”

The storm door has definitely swung open as the year winds down.

“A conveyor belt of low pressures is moving into the area — this would make for quite a wet ending to 2021, but it`s a little to far out to put too much emphasis on that,” weather service forecasters said. “It will be something to check in on as the week goes on.”

Forecasters were predicting 2.3 inches rain through Dec. 25 for San Francisco.

“If verified, it will bring SF back to top the ten wettest water years to date by the end of the week,” they said.

READ MORE: Big Sur Residents Told to Boil Water Due to Possible Wildfire Damage to Utility

The coastal mountains in the North Bay could see 3-5 inches with up to 6 inches of rain over the higher peaks. In the Santa Cruz Mountains another 3-6 inches could fall in areas already saturated by rain last week.

“Good news is that rain totals are spread out over many days which should mitigate major impacts,” the weather service tweeted. “But be prepared for minor flooding, slick roads, and potential for debris flows/mudslides.”

In the Sierra, a winter weather advisory went into effect at 7 p.m. Tuesday and will transition into a winter storm warning by Thursday morning running through Sunday.

“Heavy snow expected (beginning Thursday),” the weather service in Reno warned. “Total snow accumulations of 2-to-4 feet up to 4-to-8 feet above 7,000 feet. Wind gusts to 40 mph, with ridge wind gusts exceeding 100 mph likely.”

For the thousands who will be traveling from the Bay Area to Tahoe for the holiday weekend it means it will be a slow go.

MORE NEWS: Hazardous Sneaker Waves Threaten San Francisco Beachcombers

“Once the snow starts (Tuesday) evening, travel across the Sierra will become progressively more difficult to near impossible at times through this weekend,” the NWS Reno forecasters warned. “Be prepared for long delays and quickly changing conditions over area passes.”