Convection » Severe Thunderstorms What Happened?

On 3 May 1999, a major tornado outbreak occurred in parts of Oklahoma and Kansas, with 10 tornadic supercells and a total of 74 tornadoes reported. At least 4 of the tornadoes were F4 or F5 intensity.
When we compare the afternoon sounding (0000 UTC 4 May) with the morning sounding (1200 UTC 3 May), we see that significant warming of up to 4°C from the surface to 600 hPa took place during the day. The vertical wind shear also increased. Also note some moistening of the boundary layer occurred. The 0000 UTC sounding was taken when a supercell thunderstorm producing an F5 tornado was located about 40 km west-southwest of the launch location.
Reference: May 3, 1999 Oklahoma/Kansas Tornado Outbreak