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

GPS logs:

(From Sidney to Rapid City)


(During the chase near Rapid City)


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:


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:


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.


After merger:


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.


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.


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:


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.


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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