When to replace a roof in San Antonio: hail, heat and the mild months

Spring is hail season in the Bexar County record

Spring is when the hail stories are made. Of the 363 Bexar County hail reports of an inch or larger in NOAA's Storm Events Database since 1996, 158 came in April, 91 in May and 61 in March. April alone holds more reports than every other month outside the March to May window combined. The Weather Service calls the April 12, 2016 storm the costliest hailstorm in San Antonio history, and the 1996 to mid-2026 extract carries other spring days too.

What spring means for a re-roof is not that you cannot replace a roof in March, April or May. It is that an open roof mid-storm has nothing between the house and the weather. A re-roof in spring plans around the forecast; shingles going on a roof depend on the weather window the day gives them. The hail damage article walks what the stones do to a shingle, a panel and a tile roof.

A long hot summer

Heat is the long piece of the San Antonio year. San Antonio International averages 122.4 days a year with a high of 90 degrees or more, and 81.4 of them fall in June, July and August, and 17.7 days a year at 100 degrees or more. August is the warmest month, with a normal high of 96.0 degrees and a normal low of 74.9. The hot stretch is longer than summer itself: the station averages 15.4 days of 90 degrees or more in March to May and 25.3 in September to November. The National Weather Service also ranks 2024 as San Antonio's warmest year on record (73.3 degrees on average), with 2025 and 2023 tied next at 72.6.

ARMA, the shingle makers' association, writes directly to that heat. Asphalt shingles are used in desert and tropical regions, and in hot weather they become more flexible, so rough handling can tear them or break the laminating adhesive on multi-layer shingles. On the install itself, most asphalt shingles are manufactured with a thermally activated sealant that bonds them together once they are applied to the roof and exposed to a sufficient period of heat from sunlight; the adhesive underside of self-adhered water protection membranes is more aggressive in hot weather, so extra care may be needed when installing them; and pneumatic nailer pressure settings are adjusted as roof temperatures change, to avoid overdriving or underdriving fasteners.

On storage, shingles are best kept in a cool, dry place, not in direct sunlight for any extended time before installation, though they are designed to withstand direct exposure to the hot summer sun after installation. The bundles waiting on a driveway in August belong in shade.

Fall rain and the second wet hump

San Antonio has two rain humps, not one. At San Antonio International the normal spring (March to May) rain is 9.13 inches and the normal fall (September to November) rain is 9.71 inches, against 5.70 inches in winter. May is the station's wettest month on average, at 4.40 inches, with September (3.88) and October (3.75) close behind. A re-roof worked around spring and fall rain is normal; an open roof watches the sky.

Freezes are rare but real

A freeze on a San Antonio roof is a short stretch of the year. At San Antonio International the station averages 14.0 freeze days a year and 0.4 days at 20 degrees or below, and the median freeze window runs from November 28 to February 26, a growing season of 277 days. January is the coolest month, with a normal high of 63.3 and a normal low of 41.0 degrees.

Cold matters for a shingle install. The shingle maker GAF writes that its self-sealing shingles bond with sun and warm temperatures, may never seal if damaged by wind first, if surface temperatures stay too low or if the sealant gets dirty, and must be hand sealed in prolonged cold or where airborne dust or sand is expected before sealing. After installation in the colder months, ARMA names cold curl, a normal lift at the shingle edges caused by contraction of the asphalt coating, which should correct itself when the roof warms up.

Reading the roof and the forecast together

The maker's instructions carry the install side: temperatures, sealant, hand-sealing when the weather calls for it, and nailer pressure for the roof surface that day. Our roof replacement service walks the whole scope. If a storm set the question up, storm damage roof repair and roof repair are the pages for the before-the-replacement conversation, and roof leak repair is where to go when water is already coming in. The metal roofing service page carries the choice between a shingle re-roof and a metal one, and the roof inspection page is where the look at the roof starts when the question is open.