An estimated 120,000 customers were without power as ice-laden branches and trees crashed through power lines, the Seattle Times reported.
One man was killed in the Issaquah area when a tree landed on him and runways were closed early in the day at Seattle-Tacoma International Airport.
The National Weather Service said it was the first ice storm to hit the Seattle area since 1996.
Gregoire's emergency proclamation waives hours of service for drivers of trucks hauling intrastate bulk milk shipments and allows the activation of the Washington National Guard, if necessary.
"This is purely a precautionary measure," Gregoire said in a statement. "So far, we haven't received any requests for state assistance -- but we know weather conditions are rapidly changing. I want to make sure we have every resource available to ensure our communities are safe."
"This proclamation would allow us to activate the National Guard if we need to. It also allows state agencies to respond quickly to any storm-related requests from cities and counties for state assistance. A brief waiver of the restrictions on dairy truck drivers' work hours is needed now to avoid shipment delays that could mean the loss of nearly $1 million a day for the state's dairy industry."
The winter storm was expected to move east Thursday bringing snow into the Dakotas and the Upper Midwest after midnight, AccuWeather.com reported.
Chicago was told to expect more than six inches of snow beginning Friday morning, the Chicago Tribune reported.