I observed 3 tornadoes in far north central South Dakota, most notably an EF-4 tornado near Bowdle, SD. I was fortunate to share this experience with Derek Deroche, Lauren Hill, Amos Magliocco, and Chris Hill. This long-lived tornado was on the ground for 35 minutes (6:10-6:45 pm CDT) and produced some of the most violent motion I've observed to date.
We departed around midday from North Platte, NE with an initial target near Pierre. By mid-afternoon near the triple point, we noted a small, congested area of towers in the vicinity of Akaska, SD and quickly moved northward to intercept the developing CB. The storm steadily increased in organization and intensity, both from a radar and visual standpoint. It eventually formed a nice overshooting dome and crisp, continuous updrafts on the western flank. The photo above was taken at 5:41 pm CDT, approximately 30 minutes before we first observed a tornado.
We quickly positioned ourselves in a favorable viewing area, turning east on Hwy 20 and then north on Hwy 47 and stopped south of Hwy 12. Shortly after 6 pm CDT, it was obvious a tornado was imminent and at 6:10 pm CDT a cone tornado condensed from a rapidly rotating lowering. I pulled off on 139th St and snapped the image above. Contrary to the preliminary NWS survey, this was the beginning of the Bowdle long-lived circulation (only 1 tornado). This intense surface rotation would persist for 35 additional minutes, eventually ending near Hwy 47 several miles north of Bowdle.
I bumped up Hwy 47 and stopped shy of Hwy 12 by 2 miles with a spectacular view to the west over Spring Lake. The tornado was quickly approaching and crossed this exact photo location within a couple minutes of departing, resulting in several power poles blown down.
The tornado continued to move northeast and we repositioned along Hwy 12 for a quick view. The overall circulation began to expand at this juncture after crossing Hwy 47 with a widening debris whirl. With the tornado again approaching our location and the uncertainty of the expanding width, we wisely shifted eastward.
East of the tornado at a safe distance, we watched the tornado condensation begin to expand to meet the earlier noted ground circulation. The vortex crossed Hwy 12 and grew into a wide cone to borderline wedge. It was also at this location that the audible waterfall-sound of the tornado was most prevalent.
The tornado began to move more east-northeast and with it in close proximity, we decided to stay along Hwy 12 for quite some time to parallel it. I glanced to the west and noticed the sun was close to breaking out, and while it failed to become entirely exposed, sufficient lighting illuminated the tornado a nice white. A large debris whirl was now persistent and the rotational speeds were increasing. While photographing the tornado outside along Hwy 12, bouts of intense RFD wind and precipitation would slam into us, with peak wind gusts estimated near 80 mph.
The tornado was quickly maturing and formed into a wide cone. The updraft structure above was incredible with a seemingly wide RFD slowly peeling back the layers of the updraft.
I made one final stop along Hwy 12 at the intersection of 325th Ave, on the southwest corner of Bowdle. The tornado had now evolved into a legitimate wedge with continuing amazing storm structure atop. We were relieved the circulation was going to miss town to the north.
We repositioned north on Hwy 47 and stopped 1.5 miles north of Bowdle, across from the Redeemer Cemetery. The wedge tornado was characterized by violent motion at this stage as it approached Hwy 47. Periods of intense RFD wind and precipitation would occasionally slam/drench us. The mobile mesonet vehicle in the foreground was with TWISTEX. VORTEX2 had declared an "off day" this particular event.
The Bowdle wedge reached its maximum width around the time this photograph was taken. The tornado is approximately 1 mile west of Hwy 47, or ~2 miles northwest of our location. The large high-tension power poles in the far foreground were individually toppled one-by-one as the edge of the circulation approached.
The eastern periphery of the tornado finally crossed Hwy 47, with the southern portion roughly 0.5 mile north of our location. The large tower to the right of the road would eventually fall as the circulation passed nearby. The tornado was quickly becoming shrouded in precipitation and high-contrast opportunities quickly dwindled. Still, visual rotational speeds were very impressive and certainly in the borderline violent category.
The hook-echo precipitation effectively began masking clear views of the tornado by 6:40 pm CDT. The photo above is the final image the tornado was visible from our location and it's notable the tornado appears to be in a slow shrinking process, albeit still likely very strong. It also appeared the tornado motion became much slower over the course of its final 10 minutes, perhaps even moving northward towards the end.
Following the Bowdle wedge, a second tornado was observed from 3 miles east of Bowdle looking north at a new cyclic region of rotation. This tornado persisted for roughly 5 minutes and certainly was not as intense as the former.
We flanked the storm and took Hwy 253, pulling over 2.5 miles north of Hwy 12. We found another cool foreground location with two
lakes on both sides of the road. Inflow winds had increased, likely augmented by the approaching supercell along with the increasing LLJ. Small waves crashed along the eastern shoulder of the highway. Storm structure was quite impressive with a well-formed vault and pretty striations. We observed a third, multi-vortex tornado that intermittently was visible when the precipitation curtains thinned. One big change from one hour prior was the emergence of a very wet and expansive hook. This would only get worse with time, with the supercell evolving into a HP structure prior to sunset. We followed the supercell to Ipswich and called off the day as both gas and daylight were becoming limited. Several of us met up for a quick dinner in Aberdeen and then made a drive to Murdo for the night.