Good luck Bert. They had a huge storm roll through Austin yesterday. THe weather channel showed the pictures of their hail from Leander
TX. There is a storm brewing here is SA right now. I thought I could sleep in with the overcast skies and open windows but the thunder woke me up.
For you sake, I hope this just blows through, rinsing all the cedar pollen off the trees and puts some water in the falls at McKinney for you. There are other things to do in town if the weather is yucky. Just ask the rangers. There is also an HEB grocery store on William Cannon and I-35 for whatever you forget, it's about 10 minutes from the park.
Have a great time.