May 8, 2004 Western Iowa Supercells

Storm-starved after a week of fine dining and recreation forced on us by an uncooperative atmosphere, we pounced on the first opportunity for severe weather. Silver Lining Tours' Tour #1 intercepted two separate supercells during the afternoon and evening of May 8 over western Iowa. These storms developed along an outflow boundary left by previous overnight and early morning thunderstorms. We targeted this boundary early and aggressively, getting on the first storms from the first development.

Figures and Pictures:

Rapidly rotating wall cloud and attendant tail cloud is observed beneath the forward flank updraft of the first severe storm about 3 miles northwest of Jefferson, IA.	The wall cloud shrivels but is still spinning. Vigorous dirt whirls can be seen beneath the wall cloud. This wall cloud soon becomes completely undercut by outflow as the storm becomes linear and gusts out.	A new supercell blossoms at the tail end of the aforementioned convective line. This is our view of it's rear flank core to our southwest as we drive west on CRE57 towards Cooper, Iowa.	We penetrate the forward flank core near Cooper and get pelted by 1 to 1.5" diameter stones. We drive south in search of larger stones near the updraft but soon get deflected east by a reported "sherrifnado".
We emerge from the rear flank core and drive east to get a better look at the "action area". The storm is strongly undercut with outflow racing away from the storm to its south and east. However, as is so typical of these "high precipitation" storms, a narrow channel of potentially buoyant inflow air is "feeding" the updraft from the north and northeast. This airs stream becomes saturated as it encounters the cold outflow and a wall cloud forms. This wall cloud was observed to rotate quite rapidly.	The same wall cloud with a stubby tail cloud feeding it from the north-northeast along the forward flank gust front. Note both in this picture and the previous the dry air that has wrapped into the circulation, causing the wall cloud to be partially front-lit. This is the rear flank downdraft.