Complex sentence: Summer mornings are usually cool but do warm quickly before 9 or 10am but this is an unproven fact because nobody is up befor 11:30 on a nice summers day Rain showers are common, along with thunderstorms, and a few severe thunderstorms per year.
Split into simpler sentences: Summer mornings are usually cool but do warm quickly before 9 or 10am. On a nice summers day Rain showers are common, along with thunderstorms, and a few severe thunderstorms per year.