Parts of Los Angeles saw hail falling as a large breath of cold air headed south to California. The National Meteorological Service also confirmed the observation of some snowflakes.

Rivers swollen by days of heavy rain flooded parts of northern California on Wednesday, forcing hundreds to flee their homes.

However, about half of the 4,000 people sentenced to leave refused. "We want you to leave now," said Sonoma County Sheriff Mark Essick. "The roads may become impassable and you may not be able to get out."

Those who decided to stay supplied with food and drinking water.

Two cities – Guerneville and Monte Rio – were islands surrounded by water, local officials said. The only way to reach both communities now is by boat.

The inflated Russian River peaked at 32 feet on Tuesday night and could reach a height of more than 46 feet on Wednesday night, which would be its highest level in about 25 years, according to the National Weather Service.

More: More rain and snow expected in California after landslides and floods

The meteorological service issued flood warnings in the Sacramento Valley on Tuesday as tamed roadside ravines seethed with anger, and creeks rushed to the roads in some areas.

"It's mostly the small streams that have been heavily loaded," said meteorologist Craig Shoemaker at the Sacramento Weather Services Office.

Parts of northern California marked by devastating fires last year are particularly vulnerable to flooding, he said.

A rain gauge in Shasta County, near Lassen National Park, has collected more than 20 inches of rain in recent days, the meteorological service said.

Heavy snowfall in the Sierra Nevada will continue, said the weather service, and "1 to 3 extra feet of snow are possible there until Friday morning".

Mount Shasta Ski Park, located approximately 185 km north of Sacramento, was closed on Tuesday as park officials cleared the site of the dump under the snow dump the day before.

"We have not known this amount of snow for so little time," said the park on Facebook Tuesday morning. "We received 40 inches of snow on the last day and we are expecting 20 inches more today."

The snow has already buried other parts of the northwest: Western Montana campaigners are ready to rescue nearly 50 snow-capped Cascade County residents in need of help.

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Contributing: The Associated Press; The recording projector (Redding, Calif.)

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