The National Weather Service says its San Antonio records, which reach back nearly 140 years, put the average first 100-degree day at June 30 and the average last one around August 20. That is a typical window of 52 days.
The average number of 100-degree days per year has risen from about 10 across the full record to about 19 over the last 30 years, according to the same records. Recent years have varied widely. San Antonio's first 100-degree day came on May 25, 2024. In 2025, forecasters were calling for one by May 13.
The article says people planning a summer move can use these records to pick a date and plan a moving day. It also covers how to protect crews and belongings during hot weather.