Weather in San Antonio has about a 50% chance of the sunshine during the winter months and more than a 70% chance during the summer months. San Antonio Skies are clear to partly cloudy more than 60% of the time and cloudy less than 40% of the time. Average temperatures range from 50o in January to the mid 90s in July and August. While the summer is hot, with daily temperatures above 90o over 80% of the time, extremely high temperatures (100o and over) and rare.