Supercell and Late Tornado -
Sioux City Iowa

All images and text © copyright Gene Moore
unless otherwise indicated

A late day supercell developed on May 28th south of Yankton SD and moved first southeast then almost south toward Sioux City. We were north of the storm when it went up and proceeded east and south to catch the cell on the Iowa side of the Missouri River. Also there were new storms going up to our east in Iowa, but we could not catch these cells . The storm moved further "right" of the mean flow (southeast) than I expected producing a damaging tornado in Dixon CO, Nebraska. We observed the cell north of Sioux City and watched the updraft region while paralleling it south into town. I was with the BBC on this day. Our first mission was to complete the hail filming then try for a tornado. It seemed we could do both, but as usual we didn't tell the storm our plans; it had plans of its own.

  Supercell moving into Sioux City

Wide view of updraft region as supercell moves across western sections of Sioux City. A tornado warning continued on the storm since it produced damage earlier in the afternoon. Dark cloud tags would form near the ground and rotate into the base. This kept a string of tornado sightings going on the radio.

inflow into mesocyclone Strong rotation under mesocyclone
The inflow region of the mesocyclone included a combination of cool air from the northeast at low levels and southeast winds at cloud base level. The cloud base winds arced overhead into the storm with impressive banding. A strong rain and hail core is developing to the north of the mesocyclone and will track south over our position. Looking south at the updraft region of the storm. The inflow into the mesocyclone is now out of the east and northeast over our heads. Enlarging the image will show the light area where strong rotation was in progress under the mesocyclone. We are in an optical vault surrounded by rain and hail from the northeast through south.

Tornado southeast near airport We stopped briefly to photograph the hail and got over run by the core. High wind and blinding rain slowed out progress south through the city. Meanwhile a new tornado warning came out for the south side of town with a statement that a tornado was visible from the airport tower. We broke free of the main core and could see a lowering and funnel with debris to the south. Getting into position on the flooded roads took considerable time. This grab shot out the windshield shows the funnel to our south.

Tornado southeast of airport

After quickly pulling the zoom from 60 mm to 120 I got a steadier shot. We never recovered good position after this image. We were on an elevated roadway and there was no place to pull over. As we got off the highway we dropped down to where the trees obscured the debris cloud. Also low light was hurting chances for more photography.

A quick glance at the image and the funnel on the right appears to be the culprit, but there is another larger funnel to the left hiding behind some cloud tags.