October and April are the prime months for a comfortable visit to San Antonio, though the spring (when it's not raining) is ideal for seeing the scenery if you're planning to visit the missions or take an excursion into the Hill Country. Also in the spring, a celebratory mood overtakes the town during the annual Fiesta event.
From June through September, intense heat bakes the city, with high humidity to boot. If you come then, you can escape the heat with well air-conditioned inside attractions and at the popular water parks of Sea World and Six Flags Fiesta Texas.
Though not out of the question, winter snows are very rare, as are light ice storms. More expected are the heavy spring rains, which can result in flash flooding in the Hill Country.