How do you say "Thursday will be cloudy" in Chinese Is it just "星期四会阴天"? 

Also if you say "Thursday will be cloudy" it translates to "星期四有风”, so do you also say "星期四会有热”？
"thursday will be cloudy" means "星期四（是）阴天" or "星期四（是）多云". 

有风 means 'windy', not 'cloudy'. 

We usually say "星期四（天气）（会）很热”, "星期四有风”, "星期四(是)晴天”， "星期四有雨”， "星期四（可能）（会）下雨” and etc.