Grayson experiences a Humid Subtropical climate (Köppen climate classification *Cfa*). The city enjoys four distinct seasons, though summers are notoriously long, hot, and humid, with average high temperatures in July and August frequently reaching into the upper 80s and low 90s Fahrenheit (30–34 °C).
Winters are generally short and mild, with daytime highs in the 50s (10–15 °C) and nighttime lows occasionally dipping below freezing. Snowfall is rare and usually melts quickly, though the area is occasionally affected by winter ice storms. Grayson receives an average of 50 to 54 inches of rainfall annually, distributed relatively evenly throughout the year. The primary natural hazards are severe summer thunderstorms and the occasional threat of tornadoes typical of the Southeastern United States. The best times to visit are during the mild, pleasant months of spring (April-May) and autumn (September-October).