Why does Laredo and McAllen Texas get so hot during certain days in the winter and spring ?

As someone who used to work in south Texas these events were usually the result of dry air moving south or southeast into the area from central/west Texas. At this time of year the Sun is already fairly high in the sky due to the low latitude of south Texas and with the surface fairly barren in that area the air tends to warm pretty well. I noticed the dew points in that area today had fallen from the 40s and 50s into the 20s and 30s as dry air advected in from the north and northwest. This dry air usually doesn't make it to VCT or Houston and thus they do not warm as much. I sometimes chuckled when a "cold front" passed BRO and the temperatures warmed dramatically since the winds switch from moist onshore to dry offshore.