Agitated Cu: Day 6 - South Dakota

MON 01 JUNE 2015

Definitely the best day of the whole chase thus far! After some lunch in Gillette (WY) we could see some convection forming close to the South Dakota border, so we nudged a little farther east to Spearfish (SD) with some reasonable road options. The scenery is stunning in this part of the world, lots tree-covered hills and dips - but not ideal chase terrain. En-route one of our mifi units said that it had run out of mobile internet data - rather strange seeing as we only purchased it just 4 days prior. So we stopped at the Verizon store in Spearfish (SD) and spent an hour in there sorting it out.

However, nothing much was happening weather-wise by the time we left the store, so in some respects it served as a time filler while we waited for storm initiation. By this time (4pm) there was a lone storm north of Rapid City (SD) pulsing as it formed over the Black Hills and ran off to the east, collapsing only for another cell to develop over the same area and out to the east etc. From our vantage point in Spearfish (SD) it had a nicely-formed updraft and was the only bit of convection with a reasonably low base - a few other showers had formed, but were 'raining themselves out'.

We decided to head south on I-90 towards this storm, which subsequently became severe warned for large hail. The core of this storm was right over and just to the east of the interstate, so we pulled over before reaching it to assess what to do next - technically we were on the wrong side of the storm (the northern side) and needed to get through into the inflow portion of the storm to have the best seat if any tornado were to be produced. At this moment the sun came out and an incredibly bright rainbow formed right in front of us, lasting for a prolonged period of time.

Double rainbow near Piedmont (SD) with rain/hail curtains behind

Anyway, we eventually core-punched the cell and luckily only experienced some small bits of hail and heavy rain, but by this point this storm was becoming much better organised with a mesocyclone forming - the birth of a supercell. We pulled over just on the northern fringes of Blackhawk and there we sat for ages watching the rotating mesocyclone, since the storm was hardly moving. This also meant that areas directly underneath the storm received a lot of rain with attendant flood risk, and reports of baseball to tennis ball sized hail.

Short timelapse of the rotating mesocyclone close to Blackhawk (SD)

The mesoscyclone tried numerous attempts to form wall clouds, but alas failed to produce a tornado (which was always a low risk today anyway). There was a lot of chaser convergence with this storm, but on the whole everyone played well as we shifted slightly further south once the storm started to make a little progress farther south. Eventually the storm started to split in the evening, and then line-out, losing it's supercell characteristics and then rather quickly died a death, with the main active thunderstorms running off well to the east of Rapid City (SD). Soon after we booked into a hotel in Rapid City (SD) which means a drive to the east Tuesday morning to get into position...