Pacific Northwest braces for mudslides as record-setting rainfall continues
Flood waters of the Snoqualmie River surround a structure off State Route 203 during a storm in Carnation, Washington on Dec. 9, 2015. (Photo by Jason Redmond for Reuters.)

A storm system moving across the western United States will bring heavy rain once again to the drenched Pacific Northwest and northern California on Friday, forecasts said, as officials warned of renewed mudslides and flooding following the record rainfall.

In addition to more rain, strong winds and mountain snow were expected across the Cascades, Sierra and northern Rockies, the National Weather Service said.

In Oregon, where two women died in storm-related accidents, Governor Kate Brown declared a state of emergency for 13 counties. On Friday, Brown told a news conference that more than 40 landslides had hit state highways.

"Heavy rains and wind have required the evacuation of residences, and mudslides and high water have severely damaged or blocked major roadways in these areas of the state," she said in a statement.

This week's unusually powerful storms broke at least five weather records for the Seattle area, including the wettest first nine days in December, forced the closure of an interstate highway and swamped dozens of streets and bridges.

The storm felled trees, knocked out power to thousands of customers, and sent streams and rivers overflowing their banks.

Two northbound lanes of Interstate 5, which connects Seattle to Portland, had been reopened to traffic by Friday after closing due to a mudslide.

Emergency management officials in both Washington and Oregon have warned of more mudslides after days of ground saturation.

In Oregon, a 60-year-old Portland woman died in bed this week when a tree fell on her house and another woman drowned when her car became submerged in the state's north, officials said.

In a rare event for the Pacific Northwest, the National Weather Service on Thursday said it had received reports of a moderate-strength tornado in Battle Ground, Washington. Television footage showed residents clearing debris from roads and blue tarps covering damaged roofs.

NWS forecasters have also warned Alaskans about a powerful encroaching storm that could bring hurricane-force winds to the Aleutian Islands over the weekend. AccuWeather said that system could become "the strongest on record" for the region.

Meteorologists say the El Nino weather phenomenon, which can trigger above-average precipitation on the West Coast, is expected to remain strong through this winter.

(Reporting by Eric M. Johnson; Additional reporting by Victoria Cavaliere in Los Angeles and Curtis Skinner in San Francisco; Editing by James Dalgleish and Lisa Shumaker)