2015 Chase Diaries, Day 5, 6/1: Amazing Rapid City, SD Supercell

GPS logs:

(From Sidney to Rapid City)

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(During the chase near Rapid City)

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Started the day in Sidney, NE and honestly did not know what to do. Checked the HRRR and it showed a supercell develop near Rapid City along the Black Hills. I took the bait. I had no hopes of seeing anything on this day.

During the 4 hours it took to drive to Rapid City, the HRRR had completely changed its mind and developed a supercell further north in SD instead. Also, I could see towers go up west in WY. But a few storms had already developed and redeveloped along the Black Hills near Rapid City. A mess of a setup.

By the time I got to Rapid City the initial development was dead. Ate lunch and waited, reasoning that with easterly upslope winds and 82/63 at Spearfish (just to the NW), something had to give. Furthermore, minimal cumulus development could be seen northwest of the Black Hills area, despite HRRR’s instance on a massive supercell in the northwestern corner of the state. So I sat. (The HRRR ended up being complete crap and nothing developed anywhere else in SD until after dark.)

Thundershowers continued to percolate up and down for another hour and I could tell they were rooted above the surface. Their updrafts were soft for awhile, until finally:

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Nice! Something broke through the cap. Positioned myself to the north and was greeted with a solid base, not from the above tower but from a new, more surface-based cell to the SW:

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With deep convective initiation it’s often not one updraft but many that merge into each other and grow. I have a hunch it’s some angular momentum transport that gets the final product spinning and beasting, whereas it might be more difficult for a single updraft in a streamwise vorticity poor environment. This evolution seemed to be the case here, as a new cell to the left merges into the old one on the right.

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After merger:

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30 minutes later, a single, rotating updraft emerges, and clouds are wrapping around it. A severe thunderstorm warning is issued. Shortly after this photo, rain/hail begins to fall as the forward flank of the cell encroaches upon my location.

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I reposition myself to avoid the precipitation, only to find myself in hills and forest. I find the first clearing I see to photograph the now potent cell. The structure is really becoming awesome now.

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By this time the cell was not moving east with the mean wind but rather backbuilding and right-turning to the south and SSW. So once again I start getting hailed on and I move further south. Now I find an awesome clearing, an overlook to the valley below. Meanwhile the supercell stalls and I am in heaven.

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Here I meet some other storm chasers from Belgium. We are the only chasers at this location.

The forward flank of the storm hits me again, and again I reposition, to the valley floor east of Blackhawk. The storm structure (and mosquitoes) is really going crazy now, with a thick beaver tail and a tail cloud. CG activity picks up substantially.

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Note that this entire time the storm is trying to spawn a tornado, but really failing. It has a notable hook on radar as well. But the environment was just not there for a tornado. Bases too high, environmental flow too weak.

The severe thunderstorm warning now contained text with tennis ball sized hail, so I’m super scared of the hail core. Again I reposition south, to find the meso has become more round:

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I am on the outskirts of Rapid City now. Next I try to go west and SW of Rapid City, but after taking a couple of non-worthy shots I chicken out and instead find a gas station awning to cover my rental car from hail. At the gas station I watch as the supercell weakens to my west.

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All I can say is, what an amazing storm! Beautiful structure all around, and a yet-unmatched adrenaline rush to avoid getting hit by CG’s and the hail core. I’m still trying to absorb this experience. Staying in Rapid City overnight.

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