Heavy snow and torrential rain are pounding the West this Christmas weekend, posing danger to drivers traveling for the holiday.

In the Portland, Oregon, area, a winter storm watch has been issued as heavy snow threatens roads Saturday and Sunday.

Oregon Gov. Kate Brown declared a statewide state of emergency through Jan 3.

“Winter storms mean increased risk for those traveling, as well as those staying home,” she tweeted. “Please make a plan with your family now and be prepared.”

In Seattle, residents are bracing for snow and dangerously cold temperatures over the next week.

Mayor Jenny Durkan tweeted, “We’ve declared an emergency to allow Seattle to marshal full resources required to protect residents, provide warm spaces & support our frontline workers.”

The mountains are also dangerous. Through Monday, several feet of heavy mountain snow is forecast for the Sierra Nevada mountain range in California and the Cascade Range in Oregon and Washington.

Rain is also threatening Southern California. Downpours could trigger areas of flash flooding, mudslides and debris flows, especially across wildfire burn scar areas.

ABC News’ Dan Peck contributed to this report.