The US Army, back when there were many uniform variations specified in regulations dates for wearing warm weather and other weather uniforms. It varied by geographic location. Generally in most of the Original 48 states, as best as I can remember, the warm weather uniform could be worn from April 15 to October 15. Also, those are the dates when the furnaces were lit, or shut down. Sometimes we got awful cold wearing warm weather uniforms on very chilly days. Air conditioning, that is air cooling, was not government issued in those days. I'd wear a white mess jacket during that six-month period and not feel freaky.