This loop of GOES-8 Sounder-derived Lifted Index (LI) shows the instability of the air mass that was being advected northeastward into Arkansas and the southern Mississippi valley region on 21 January 1999. LI values less than -8 C (red enhancement) were seen after about 14:00 UTC. ETA model 850 hPa wind streamlines are plotted at 6-hour intervals on the imagery.