BLUE CANYON (CBS13/AP) – The latest on the “bomb cyclone” hitting Northern California on Tuesday:

Share your weather photos from the bomb cyclone here.

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9:38 p.m.

State Route 20 is closed from 0.4 miles east of Nevada City to the junction of Interstate 80 due to multiple jackknifed big rigs, according to Caltrans.

Chains are required on all vehicles except 4-wheel-drive vehicles with snow tires on all four wheels from six miles west of Grass Valley to the junction of I-80.

5:30 p.m. 

Caltrans filly reopened both directions of I-80 from Alta to the Nevada State Line after multiple collisions.

Officials are asking drivers to please slow down and use extra caution as they make their way through the snow.

2:30 p.m.

Traffic is now being held on westbound Interstate 80 in Truckee due to multiple collisions, California Highway Patrol says.

Eastbound I-80 traffic is being held at Alta for the same reason.

The traffic hold comes as snow started to move into the region.

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Snow is also starting to fall at lower elevations, like Grass Valley.

1:43 p.m.

Northern California is starting to see the first effects from a “bomb cyclone” weather phenomenon that’s expected at one of the busiest travel times of the year.

The National Weather Service says the storm expected Tuesday into Wednesday could be like nothing experienced in the area for 20 years.

As of 1:30 p.m. Tuesday, chain controls are in effect on both directions of Interstate 80 from Donner Lake Road to Cisco Grove.

A little after 2 p.m., chain controls also went up on Highway 50. Drivers will need chains from Twin Bridges to Meyers.

Wind gusts of 75 mph (120 kph) are expected in some areas and waves of 35 feet (10.6 meters) or more could slam the coast.
Mountain passes in northern California and southern Oregon could get up to two feet (0.6 meters) of snow.

The center of the low-pressure system is expected to make landfall late Tuesday afternoon between Crescent City, California, and Brookings, Oregon.

A “bomb cyclone” forms when air pressure drops by 24 millibars in a 24-hour period.

Forecasters say this storm’s air pressure has dropped even more quickly than that.

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Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.