June 24, 2008 — Supercell evolving to massive high-precip, outflow dominant "washing machine" [Mott, ND to McLaughlin, SD to Selby, SD to Agar, SD]
Vince and I targeted the North Dakota area along I-94 near Dickinson or so, but after a hearty lunch at a favorite mexican restaurant in Spearfish, SD, we got on the road about Noon MDT. By the time we reached Buffalo, SD, there was already a severe storm underway just north of I-94 north of Medora, ND. This storm was moving quickly to the east and evolved into a large hail producing storm just north of the interstate. It was quickly advancing east of our current longitude, so once we reached Bowman, we decided on a different strategy. We optioned east on Hwy 12 out of Bowman. While doing so, a small storm developed essentially right on top of us as we were driving east. It had a real small base without much substance, but we pushed on eastward nevertheless. Meantime, a few strong to marginally severe storms were developing along the Hwy 85 corridor from Buffalo to Belle Fourche, SD. These storms developed in the more capped atmosphere and we figured these storms didn’t stand much of a chance of doing much. We also monitored the continued southward development/propagation of the complex of severe storms along I-94. Some of the biggest updraft cores with this complex were beginning to turn more to the right…and as we continued east, all this activity to our north was becoming more "in play".
Eventually that small storm that was over us began to move closer to the "main complex", and as it does so it began to strengthen. This storm finally began to take on some supercell characteristics between Haynes and Mott, ND. We reached Thunder Hawk, SD (basically right on the SD-ND state line) and drove north about 6 miles to a nice stopping location to film and photograph. We sat there for probably an hour watching this nice flat updraft base evolve into supercell structure with scud forming and rising into the updraft to form a wall cloud in time. There wasn’t much rotation with this feature, and I noticed this arcus cloud behind our storm…which was the leading edge of the northern complex about to overtake our southermost supercell. Then the "race chase" was on. The supercell we observed became absorbed into the big severe complex and was rolling east-southeast at a 40-50mph clip. We followed this thing on Hwy 12 from Thunder Hawk all the way to Selby, crossing the Lake Oahe along the way. Highway 12 paralleled this storm almost perfectly for quite some time…and we stopped a number of times to watch the well-structured, multi-tiered shelf cloud and dust approach rapidly. This stuff was moving fast — a forward-propagating severe complex. At sunset, the colors and contrast were superb along Hwy 83 from Selby to Agar. It was a fun chase with great colors/contrast once again from nicely structured outflow-dominant severe storms over beautiful country. We stayed in Pierre, arriving about 11:15pm CDT or so.