Nothing in SW Houston.  Whoever is seeing "sleet", are you sure it's sleet and not graupel?   Sounding has all precip forming in sub-freezing air above 700mb, which should be snow.  There isn't any above-freezing followed by another sub-freezing layer (which would produce sleet) indicated. See the sounding below.  
Could super-cooled water above 12,000 ft be going directly to ice vs. snow crystals to produce sleet?  Or are we seeing graupel, which is partly melted and re-frozen snowflakes?  Graupel is round like sleet but much whiter and softer (generally).
This is what graupel looks like:

Latest Houston Sounding:
