Severe Weather and Flash Flooding from Supercell Thunderstorm - June 16, 2006

Severe Weather and Flash Flooding – 16 June 2006

Street flooding in S. Sioux City, NE. Photo provided by KMEG viewers.

Event Summary:

On 16 June 2006, severe thunderstorms moved across southeast South Dakota and northwest Iowa, leaving two swaths of damage in its wake (Fig 1). Shortly before 3:00 PM CDT, a small line of severe thunderstorms began moving into southeastern South Dakota from north central Nebraska (Fig. 2).

A well-defined supercell (Fig. 3) entered extreme southeastern Charles Mix and southern Bon Homme counties at 2:51 PM CDT, and as it tracked east-northeast through Bon Homme, Yankton, Turner, and Lincoln counties, hail up to baseball size and winds as strong as 75 mph were reported in association with the storm. At the same time, a smaller severe thunderstorm (Fig. 4) which formed in western Plymouth county, IA, was tracking north-northeast through northwest Iowa, dropping penny-sized hail and damaging buildings with up to 70 mph wind. The two storms weakened and merged near the triple point of the three state borders around 4:45 PM CDT, and then joined a strengthening multicell line of thunderstorms moving northeast out of northeast Nebraska (figure 5).

As the line progressed through northwest Iowa and southwest Minnesota, heavy rain fell with totals over 3.5 inches in some areas (Fig. 6), and created flash flooding in Sioux City and Le Mars, Iowa . Although the thunderstorms were no longer severe, rain and isolated thunder continued throughout the tri-state area until finally exiting the area after 4:00 AM CDT on the 17th.

Figure 1. Severe thunderstorm tracks across southeast South Dakota and northwest Iowa.

Figure 2. Radar reflectivity at 2:43 PM CDT showing severe storms leaving north central Nebraska.


Figure 3. Radar reflectivity (L) and storm	relative velocity at 2:51 PM CDT.

Figure 4. Radar reflectivity of the second severe cell in Sioux County, IA at 3:55 PM CDT.

Figure 5. Radar reflectivity from 4:46 PM CDT showing the merger of two severe cells and the multicell line.

Figure 6. Radar estimated storm total overlayed with observed precipitation totals for June 16.


Street flooding in S. Sioux City, NE.	Photos provided by KMEG viewers.