While the above radar image (taken from the Corpus Christi, TX site a few moments ago) does not show widespread "precipitation", if you look closely you'll see the little blue balloons with 3 dots inside. That signifies reports of freezing drizzle and/or freezing rain, which are increasing across deep South Texas.
This trend is taking place as moist air just above the surface is being lifted up and over the cold air in place at ground level. The moisture freezes on contact since surface temperatures are at or near freezing.
Periods of freezing drizzle, light freezing rain and/or sleet will continue to develop and spread Northeast along the coast this evening. The precipitation is likely to trend more toward a sleet and/or snow mixture overnight and Friday morning. Light ice accumulations and 1-2 inches of sleet/snow (with localized amounts near 3 inches) are likely in this area. This would include the Houston and Corpus Christi areas.
Further west, along the I-35 corridor, flurries and very light snow should begin anytime after 6 o'clock this evening. The atmosphere just above the surface continues to slowly moisten, and that, combined with the approaching upper-level weather disturbance from the southwest, will start squeezing very light precipitation out of the clouds later this evening. Light snow and flurries have just begun to be reported in the Laredo area during the past hour.
The oblong, light to medium grey shaded region just Northwest of the Big Bend (over the Midland/Odessa area) on the water vapor image above signifies the leading edge of the upper level weather disturbance that is expected to bring wintry precipitation to the region overnight and early Friday.
This system will continue to lift East/Northeast across the region overnight into Friday morning, increasing precipitation intensity at the same time.
Along the I-35 corridor (including Austin and San Antonio), widespread snowfall of 1 inch, with localized amounts near 2 inches, can be expected overnight into early Friday. The Northern and Eastern portions of the region stand the best chance of seeing 2 inches, and areas East/Northeast of I-35 toward the upper coastal bend and east-central Texas are more likely to receive 2-3 inches.
Below are the probability maps for 1, 2 and 4 inches of snow or more across the region tonight through Friday morning, as prepared by the HPC:
A Winter Weather Advisory (light purple shading on the map below) is in effect along the I-35 corridor and parts of northeast Texas tonight into early Friday. A Winter Storm Warning (pink shading on the map below) is in effect further East across the remainder of eastern and southern Texas: