The hottest temperatures of the year thus far are expected this week in Northern Arizona. The National Weather Service says high temperatures are expected to be ten-to-15 degrees above normal by Wednesday. A high pressure ridge continues to build, which is responsible for the rise in temperatures. Temperatures will decrease by the end of the week, with a chance of dry thunderstorms starting Friday. Highs are expected to reach the upper-80s in Flagstaff and the mid-90s in Prescott on Wednesday.