By Renée Santos

SACRAMENTO (CBS13/AP) – A cold, late-winter Pacific storm brought rain and snow to California on Tuesday.

Winter storm warnings were posted or scheduled to take effect during the day in mountains from the Oregon border south to the U.S-Mexico border.

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Scattered thundershowers were expected to arrive in the Sacramento region by 11 a.m. and would build as the day progressed.

Pop-up showers dumped rain over the Yolo Causeway Tuesday and some people were unprepared for the change in weather. CBS13 spotted a man running to his car after getting caught in the rain.

And a delivery driver near the end of his shift said the weather was terrible. He was trying to keep products dry before the rain picked up again.

“It gets wet, it should dry off in the cooler but still these aren’t the conditions you want to be in,” the man said.

A significant amount of snow is expected in the Sierra.

See the latest conditions on the CBS13 weather page

Mountain travel was discouraged due to the potential for major delays, chain controls, and near-whiteout conditions, the National Weather Service said.

The snow caused crashes and traffic backups. A semi-truck spun out coming to rest in the wrong direction on Interstate 80 near Nyack, and the slippery roads are only expected to get worse.

Elaina James was unaware of the Sierra travel warnings.

“I thought about that we were just like if it gets bad, we are going to stop,” she said.

A combination of strong thunderstorms and heavy snow is making travel difficult and dangerous. James is offering words of advice as conditions worsen.

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“Know what you could possibly get into, be prepared,” James said.

The San Francisco Bay Area weather office warned of possible hail, thunderstorms, and downpours that could make driving risky.

Early morning lighting was observed offshore west of Pebble Beach.

The storm was expected to begin affecting the southern half of the state Tuesday night and last into Thursday.

SACRAMENTO VALLEY FORECAST

TUESDAY: Cloudy and rainy with a high of 57 and a low of 42

WEDNESDAY: Cloudy and rainy with a high of 55 and a low of 43

THURSDAY: Cloudy and rainy with a high of 59 and a low of 38

FRIDAY: Cloudy with a high of 66 and a low of 37

SATURDAY: Cloudy with a high of 66 and a low of 38

SUNDAY: Mostly sunny with a high of 67 and a low of 42

MONDAY: Cloudy with a high of 63 and a low of 41

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California needs all the precipitation it can get after a largely dry winter. The Sierra snowpack was well below average in the most recent survey by the state Department of Water Resources and rain gauges elsewhere haven’t had much to measure.