First lowering of the day forming underneath one of the stronger updrafts on a broken line of storms near Vermillion, SD.

Underneath a shelf cloud with a lot of undulations near Mayfield, SD.

2 separate mesocyclones on the storm interacting with the warm front near Chester, SD. The far meso was the one right on the boundary.

Another shot of the meso's. The far one had a lowering as it was interacting with the warm front.

Terrific structure with this storm.

As we approached the base, this bowl shaped lowering was showing rotation and there was a moment where condensation into this area was occurring rapidly. Closest any storm came all day to producing a tornado. This was just north of Chester, SD.

New cumulus towers going up ahead of the low on an occluding boundary.

Underneath the line of updrafts near Salem, SD. This was quite the scene with a lot of motion going on and possibly a few vorticity rolls at some of the cloud bases.

SPC MD issued at 10:24am CDT, highlighting the risk for tornadoes ahead of the triple point and on the warm front.

STORM PREDICTION CENTER OUTLOOKS:

STORM REPORTS:

MAY 10, 2015 CHASE LOG: SOUTH DAKOTA

This chase was a rather frustrating one, but at least we saw some good storms! We left early (around 9am) in hope of getting to southeast South Dakota in time to see storms initiate around 2-3pm. During the 4 hour drive to the target area, a tornadic supercell developed just ahead of the low after only a few hours of heating, dropping a tornado from 10:30-11:00am in the morning! Unfortunately, the EF-2 tornado brought significant damage to the town of Delmont, SD. I could not believe a tornado could form that early as it did. This tornado formed ahead of a strong low pressure system that had been leading to widespread severe weather/tornadoes in the Central and Southern Plains over the past few days. This was mainly a shear driven event as even marginal instability was enough to lead to tornadoes. As you can see in the image above, the set-up consisted of a low pressure center lifting north into southeast SD along with a warm front, while a trailing dryline and cold front moved very slowly north-northeast.

A mesoscale discussion was issued by the Storm Prediction Center already by 10:24am, talking about issuing a tornado watch. This tornado watch soon followed suite at 10:45am until 9:00pm in the evening! A long day of chasing awaited us. We were on our first severe warned storm coming out of northeast NE to near Vermillion, SD shortly before 2pm. This storm had a decent lowering but never could get its act together and congealed into a cluster of severe storms with the main threats being large hail and high winds. At the same time, a new tornado warned storm developed northwest closer to the triple point near and north of Freeman, SD. This storm did not drop a tornado, but certainly looked the part for a while. After chasing new storms north to near I-90 west of Sioux Falls, one storm held promise as it approached the warm front near Chester, SD. This storm had two rotating mesocyclones, one that was very pronounced and had great structure to our north as you can see in the photos. The storm ended up weakening upon moving north of the warm front so we dropped south back to Sioux Falls to await round 2.

The next line of storms developed by late afternoon along the occluding low pressure system near Mitchell, SD. The storms were low topped and one became tornado warned that we were not on north of Mitchell that came close to producing a tornado. We were able to get on the southern storm near Spencer, SD and followed the storm north. This storm exhibited some strong inflow and a rotating wall cloud with condensation into the base. It was clear this storm was close to produce a tornado, but it appeared to weaken upon after its first cycle. We left this storm and dropped south as all storms prior had weakened after the first cycle and did not appear to do anything else. This was the exception in which the storm was reported to produce a brief tornado after we left it, but I have yet to see photos. Certainly could have as the storm intensified upon reaching the warm front and it was certainly a mistake to leave it when we did. A learning experience!