Central Texas has hot, humid summers — Killeen regularly hits the mid-30s°C from June through August, and the heat can make outdoor activities at the lakes less pleasant during the middle of the day. Spring (March to May) and autumn (October to November) are the most comfortable seasons: warm enough for swimming and hiking, cool enough to enjoy being outside. Spring brings wildflowers across the surrounding Hill Country, and the lakes are at their most inviting before summer crowds arrive.
Winter is mild by northern standards — frosts occur but snow is rare — and the Belton Lake Christmas light display draws visitors in December. If you are visiting someone stationed at Fort Cavazos, timing often matters less than convenience; the base and its museums are accessible year-round.