(Portland, OR) -- The hottest weather of the year will arrive in Oregon starting on the Fourth of July. The National Weather Service says there is a "Moderate Heat Risk" Thursday through Sunday. The Willamette Valley could see temperatures reach 100 degrees starting Friday. People attending the Waterfront Blues Festival are advised to be prepared for the heat. In Southern Oregon, an Excessive Heat Watch takes effect Thursday for possible temperatures between 100 and 110 degrees.