The above map from the SPC in Norman, OK shows a "slight" risk of severe weather for much of southcentral and southeast Texas overnight tonight.
In meteorology this is what we call a "conditional" risk of severe weather. By that I mean that it is uncertain that thunderstorms will develop, but if they do then they are likely to become strong to severe.
A strong upper-level weather disturbance, currently lifting Northeast across Mexico, will move across the region overnight. Southerly winds have brought an increasingly moist airmass Northward across Texas today, and this moisture will interact with the disturbance to produce widespread showers across the region overnight and early Sunday morning.
A few thunderstorms could also develop overnight, and if so, are likely to produce hail to severe limits. Gusty winds are also possible.
At this time, it appears that the best chance of thunderstorm development will take place after 3 a.m. central time, into the early morning hours on Sunday.