(Reuters) – Powerful storms packing heavy rain and snow will lash the U.S. West on Tuesday, a day after thousands of people fled their homes to escape floods, forecasters said.

A band of heavy downpours will drench northern California and heavy snow will fall in the Sierra Nevada mountains into Wednesday, exacerbating the threat of flooding, the National Weather Service said.

The storms are part of weather system called the “Pineapple Express” that has soaked a vast area from Hawaii to the typically drought-prone states of California and Nevada.

Just north of San Francisco, the Russian River in Sonoma County flooded early on Monday, forcing the evacuation of more than 3,000 residents, officials said.

In Nevada, residents of about 400 homes in Reno were ordered to leave as rains swelled the Truckee River, which flows through the city, a county official said.

A woman died after she was struck by a falling tree in the San Francisco area, local officials and media reported.

Over the weekend, an ancient giant sequoia tree with a hollowed-out tunnel was toppled by floods in Calaveras Big Trees State Park just southeast of Sacramento.

California’s Napa Valley vinyards largely escaped undamaged and the rain was expected to replenish water supplies after five years of drought, said Patsy McGaughy, Napa Valley Vintners spokeswoman.

California officially remains in a state of drought as water is still scarce in the south.

But northern California’s Lake Oroville, the principal reservoir for the State Water Project, has 2.25 million acre feet of water, more than double the amount it had a year ago, Michael Anderson, state climatologist for the California Department of Water Resources, said.

(Reporting by Brendan O’Brien in Milwaukee)