This loop of GOES-8 6.7 micrometer IR ("water vapor") imagery shows the approach of a shortwave trough from the southern Rockies. Strong divergent flow associated with this shortwave helped to enhance synoptic-scale upward vertical motion across northwest Texas into southern Oklahoma. Note the small pocket of "thinning" cloudiness along the eastern edge of the main cirrus band -- additional heating within this small region may have played a role in the rapid destabilization of the air mass over southwestern Oklahoma after about 20:00 UTC.