We had snow on Christmas eve in 2004. It was gone and I was back in my shorts and flip flops by noon Christmas day. I'm close to Galveston and we haven't had a freeze in two or three years.
Come on down to say howdy. The air is warm and the margaritas are cold.
It can get windy in the valley and there may be a cold snap for a week or so in the hill country. If you can plan it to have a secondary location in the valley tour the hill country until threatened with a cold spell. Go on down to check out what the valley has to offer and then move back up once that pesky cold air has moved on.
There is a saying here in Texas; if you don't like the weather stick around, it will change.