It is getting close to actual summer and our weather has suddenly turned warm. But here in the Northern Plains, we know it is unlikely to remain warm all summer. Cold snaps can happen even at summer’s peak, making a light jacket feel good on our arms. But if you like your weather warm and sunny and are planning a summer vacation, then the best time for your summer vacation is likely to be sometime between the end of the first week in July through the end of the second week in August. Roughly, this is the time between July 7 and August 15. Of course, in any given summer, the hottest weather could happen anytime. But on average, this is when it is most likely to be sunny and warm. Meteorologist John Wheeler.