You're more likely to be cold in New Mexico and Arizona than west Texas.
Likely WORST case weather in Texas is cold rain from Louisiana to San Antonio, then windy cold, with perhaps rain or sleet to El Paso, but both conditions never last more than a couple of days. You're just as likely to have something like today, where it's clear, going to be 71 in central Texas.
Naturally, having said the above, I picked my new bike up in Albuquerque last February, had perfect weather down to Fort Stockton, and from that point east to Austin had sleet, million mile per hour tail wind, temps dropped steadily into the 30s, the next morning for the last leg it never got above freezing...exactly the opposite of normal pattern. I was NOT prepared for such cold.
The Albuquergue dealership, Sandia BMW, is great, by the way.