Friday 8 June 2018

Day 13 - South Dakota / Nebraska

FRI 08 JUN 2018

We headed north after lunch in Chadron (NE) across the border towards Buffalo Gap (SD) towards a supercell that had developed over the Black Hills northwest of Rapid City (SD). Some of the CAMs (convection allowing models) were suggesting that this storm would weaken as it drifted away from the mountains, while new storms were expected to fire up well to the east.
Hand drawn surface analysis at 15z (09:00 MDT). Isobars black, isodrosotherms green
SPC Forecast
SPC Tornado Probability Forecast
Right on cue, towering cumulus were visible to our east, and so we headed towards Interior (SD) where an updraft developing overhead produced some marble sized hail and a lot of rain / lightning. This cluster of thunderstorms was fast growing in size, and we had some work to do to get around to the south side - due to limited road options we had to drive round the northern then eastern flank of this developing MCS (mesoscale convective system) in order to get ahead of it, as it began to move to the SE.

On the SE side of the storm complex, a nice gust front was visible as this portion of the storm bowed out. We ambled southwards back over the border towards Valentine (NE), with the storm, now forming a squall line, very slowly drifting southeastwards towards us. The storms were very active with lightning, but most was inter-cloud or hidden in the wall of rain - with, by this stage, very little cloud-to-ground lightning, and hence not much worth taking a photo of.
Gust front to the west of Mission (SD) 
Mammatus to the south of Valentine (NE)
Eventually we gave up as darkness fell and found a hotel in Valentine (NE) where we sat and let the storms pass over us - some of the cloud-to-ground lightning was very close with near-instant thunder.

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