Less than an hour north of Bay, we have heavy red clay under 8-10" of sandy loam. Its not easy to dig it. I know 'cause we've been digging 3' fence post holes!
I would love to have a storm shelter in the ground, but not sure it's gonna happen. In the mean time, our house was built with the walls & roof attached with "hurricane straps" and the exterior walls, roof joists & floor all have spray foam insulation, which makes the house stronger in a storm. The house is built on an 18" wide footer - rather than pier & beam like many houses in Texas. Not perfect, but we have an interior bathroom that we plan to use for shelter if we get a bad storm headed our way.
I sure miss the basements we had in MN & PA! In PA we had the perfect alcove, in our basement, in the event of a tornado. But, thankfully we never had to use it!
When I lived in Lake Worth (NW Ft. Worth), we had a MASSIVE thunderstorm build over us. The clouds built at least 5 miles high! By 9:00 that night the winds were howling & blowing the 10" main branches, of our 40 year old Mulberry tree, 6 feet in each direction. Eventually that big branch broke off.
As my Ex- and I watched the big branches, of the Mulberry tree swing back & forth, we realized that the lightening was flashing green, which means conditions are right for a tornado!
I ran & got the kids out of bed and we went into the crawlspace under the house. As we did, the wind sounded like a freight train was going right through our garage. We also heard hail hitting the garage door. We sat with our backs against the 8 foot brick fire place chimney, that went into the ground under the house. It was really scary!!!
It seemed to last an eternity. But, was really only about 5 minutes. When the hail & wind stopped, we went outside. It was amazing! Our solid brick house was undamaged and there wasn't a cloud in the sky! I was barefoot & walking on the grass was like walking on a sopping wet sponge!
Later we learned that a tornado had touched down in a trailer park 1/2 mile from our house! At least 20 trailers were destroyed.
My neighbor, who grew up in the Texas panhandle - aka "Tornado Alley" was really scared, by the storm. In her 55 years, she had never sheltered from a storm. But, this time, she & her husband pulled mattresses over themselves, in the hall, to ride out the storm.