SEATTLE—With temperatures in normally mild Seattle dropping well below freezing, Kaety West walked a short distance in the snow from the tent where she usually stays to find refuge at a small warming center at an American Legion hall. “I’m not even willing to stay in it right now. It’s just so difficult,” she said of her tent on Monday. Severe weather sweeping parts of the U.S. 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 spaces for people to find refuge as forecasters said the extreme cold from an arctic blast could last until the weekend. Snow showers blew into the Pacific Northwest on Sunday from the Gulf of Alaska, dumping up to 6 inches (15 centimeters) across the Seattle area and snarling traffic throughout the greater Seattle and Portland …