By MANUEL VALDES
SEATTLE (AP) — Severe weather sweeping parts of the U.S. has brought frigid temperatures to the Pacific Northwest and heavy snow to mountains in Northern California and Nevada. Across western Washington and Oregon officials and private groups opened emergency centers for people to find refuge as forecasters said the extreme cold from an arctic blast could last until the weekend. Many facilities would be open through the new year. Farther south, blowing snow in the mountains of Northern California and Nevada closed key highways, with forecasters warning travel in the Sierra Nevada could be difficult for several days.