Central Texas weather has a way of editing a weekend for you. The answer is not to plan a separate attraction for every possible forecast. It is to make one good plan that can turn gracefully.
Choose an outdoor first choice
Start with the family activity you would choose if the weather holds. Parks, public programs, and outdoor events can be excellent anchors, but check the organizer page on the day of the event. Austin Parks Foundation specifically posts weather updates for its park programming through its event channels.
Pick one indoor category, not one exact destination
Decide whether your fall-back is creative, active, bookish, or food-forward. This is more useful than obsessing over a single venue, because it leaves room for capacity, traffic, nap timing, and the opinion of the smallest person in the car.
Give the day a reset point
Rain plans work when everyone knows when the decision will be made. Try a simple rule: evaluate the weather after breakfast, then again before leaving the first stop. If the forecast changes, use the back-up category and stop adding new commitments.
Keep the useful things in the car
A small bag with dry socks, water, a layer, a book, and a snack keeps a detour from becoming a defeat. The goal is not to outsmart the weather. It is to keep the day feeling like it still belongs to your family.
A flexible plan is not a lesser plan. It is the version that survives the real day.
For outdoor event changes, check the individual organizer or the Austin Parks Foundation event calendar before heading out.