 The area sees anywhere from 1,240 to 1,440 degree days Celsius with most of these microclimates falling into classifications of Regions I and II on the Winkler scale of heat summation.On average the Columbia Valley sees over 300 cloudless days per year and experiences no more than of rainfall.The Horse Heaven Hills AVA was established in 2005 and is home of some of the state's largest and oldest vineyards.