Texas has two seasons: Hot and Scorching Hot!!  Actually, there is quite a difference in weather from the plains of the panhandle to the gulf coast or the piney woods of east Texas to the deserts of the West.  However, a general rule of thumb is that unless you plan on being indoors or in a body of water, avoid Texas from May through September as it is Scorching Hot!!  Especially during July and August!!  Those two months are dredded by all Texans, because you will be drenched with sweat if you just walk around the block.  The very best time to be in Texas is between November and March.  Texas doesn't have a winter for the most part.  Oh sure, the northern parts of the state such as Amarillo, Lubbock or even Dallas/Ft. Worth may see a few of days of ice or snow, but those days are usually few and far between.  For the most part, you can expect sunny days with very pleasant temperatures even in December or January especially in south Texas in cities like Austin, San Antonio, Houston and the gulf coast.