The Brief Desert temperatures soared to 113 degrees in Phoenix on Thursday while rain provided brief cooling in high country regions. Extreme heat warnings cover Arizona deserts through the weekend and expand to high country areas from Friday and Saturday through Sunday. Most of the High Country reached the 90s, but rain helped cool temperatures at times during the afternoon. This Weekend:Extreme heat warnings are in effect across the deserts of Arizona through the weekend, and the high country will be under the warnings starting Friday and Saturday, through Sunday. Flagstaff could tie the record for the warmest August temperature on Sunday, with a forecast high of 93 degrees.