San Antonio starts Monday, October 26, cloudy and in the mid-60s, but the day should warm quickly. The high is forecast near 83 degrees, with only a slim rain chance. Clouds are expected to linger Monday night as temperatures ease to about 66.
Rain chances rise Tuesday
Tuesday, October 27, is forecast to reach about 81 degrees, with a 40% chance of rain. Showers could develop from late morning into the afternoon, and thunderstorms are possible later in the day. Skies should turn partly cloudy Tuesday night.
Wednesday stays warm, with a high near 84 and a 30% chance of afternoon showers and thunderstorms. The bigger change is expected Thursday, October 29: showers and thunderstorms are likely, with a 70% precipitation chance and a high near 78. The National Weather Service Austin/San Antonio forecast discussion says locally heavy rain could develop Thursday into Friday, but where the heaviest rain falls and how much accumulates remain uncertain.
Rain chances remain elevated Thursday night and Friday, October 30, with another round of showers possible and temperatures near 78. Saturday brings a 30% chance of morning showers and thunderstorms before partly sunny skies, with a high near 82. Sunday looks partly sunny and warmer, with a high around 85.
Late-October storms have precedents, not predictions
South-central Texas has experienced damaging rain in past late-October storms, but those events do not establish what this forecast will bring. The National Weather Service documented heavy rain and severe weather across much of the region on October 30–31, 2015, while a separate storm system produced disastrous flash flooding in the San Antonio metro area and along the Guadalupe River on October 17–18, 1998. The 2015 account and 1998 account describe different events and conditions; neither is evidence that this week’s uncertain rain will have similar impacts.
A U.S. Geological Survey model of the San Antonio River watershed for 1997–2001 attributed about 33% of streamflow to storm runoff from various land uses, according to the USGS study. That is a historical watershed estimate, not a measure of this week’s rainfall or a forecast of flooding.
Preparedness resources are not flood predictions
For route planning, the City of San Antonio says SAFE Routes at key low-water crossings help residents find alternate routes away from flooded roads; this general safety guidance does not mean a crossing is expected to flood this week. Texas Public Radio reports that drivers can also use BexarFlood.org to check specific low-water crossings and sign up for alerts when a gate lowers.
The City of San Antonio’s 2016 Climate Vulnerability Assessment described interactive maps hosted by SARA that let residents check whether their homes were within a floodplain. That resource concerns mapped floodplain status; it does not indicate that any location will flood during this forecast.
