I have a rash on both forearms and elbows that only appears in summer months. It's itchy and seems to worsen the hotter the temperature is outside.?

Needs Exam. There are several skin conditions that have the symptoms you describe. The two most common would be eczema and psoriasis, and the treatments for each are slightly different. For short term relief, try a small amount of topical steroid like hydrocortisone, but you definitely need a doctor (primary care or dermatology) to take a look.