Like I mentioned in the May 22nd chase account, there were two other chase days that would attempt to top what I saw that day. Believe it or not, the very next chase (this chase), was one of them! This chase was so wacky in so many different ways. I hope when this chase day is showcased in an episode of StormChasers the editors portray the craziness in its gravity and its humor.
The categorical risk of severe weather was upgraded from SLIGHT to MODERATE during the morning hours. The synoptic setup was very dynamic, with a 50 kt LLJ, an 80 kt mid-level jet, and an upper level jet exceeding 100 kts. At the surface, in the morning, a warm front was draped across central and eastern South Dakota, while a stationary boundary extended through southwestern South Dakota and into Nebraska and Colorado as a cold front. The warm front lifted rapidly in advance of the approaching upper level trough and surface cyclone, which by mid afternoon was centered somewhere around the western South Dakota-Nebraska border and had deepened to 992 mb. This caused surface winds to become SSEly and accelerate to upwards of 30 kts sustained with gusts up to 50 kts. A cold front attended the advancing surface low, but it did not move east very quickly and allowed northward moving storms to ride along the boundary for longer.
Meteorological setup aside, the crew headed west from Aberdeen, and after some debate while south of Selby, continued west along U.S. 12 through Mobridge and on state highway 20 continued west to try to intercept tornado warned storms that had developed far to the southwest. The change in terrain when crossing the Missouri River in South Dakota is quite dramatic, as the flat farmlands and good road network east of the river open up wide into desolation - treeless, rugged terrain with little in the way of towns, people, or roads. We had no choice but to continue our westward trek to attempt to beat the northward moving supercells to state highway 73. After the multitude of technical difficulties that caused us to stop several times, our confidence in seeing the storms before they crossed the boundary or crossed our intended path decreased. The storms appeared to lose some organization on radar as we neared them.
Once we were within 10 - 20 miles of state highway 73, we suddenly crossed a boundary - the cold front - which featured strong northerly winds and a stark temperature contrast. Although our temperature dropped, however, the dewpoint did not, so it was really cool and moist. A few miles further west, with the storms blocking our view of the sun, we approached a deck of very low stratus/cumulus clouds. I figured that was it for seeing any tornadoes for sure. As we slipped under the deck, violent, rhythmic CGs began to strike all around us. I'm guessing they were from the anvil region of the storm. Each strike had only one return stroke, and the strikes were about 3 - 5 seconds apart. There was very little in the way of towers or power poles to attract lighting other than our cars, so I was somewhat nervous about being struck. Thankfully, there were some buttes, mesas, and higher hills to also compete for lightning strikes.
We neared our turn south on state highway 73 (we beat the lead storm!) when suddenly, the GPS signal went out in each car...all at the same time. I'm pretty sure we had driven into the Twilight Zone by this point. Especially because shortly after rounding the turn, someone got on the radio and said something to the likes of, "is that what I think it is?" They were referring to a menacing dark gray mass of cloud several miles to our south-southeast...in contact with the ground. In this environment, with cloud bases only a few hundred feet above the surface, it was honestly difficult to tell exactly what it was initially, but everyone was thinking the same thing. And we were all correct: a large tornado(1) was in progress!
The team sort of spread apart for various reasons, but Chris and I stopped soon after we saw it. This tornado was not some dinky, ropy, weak little random spin-up. It was a bona fide supercellular tornado because I could see an RFD cut almost fully occluding the tornado, and it persisted for a long time. The tornado changed shapes frequently, going from stovepipe to wedge to multiple vortex and back again in a matter of minutes. Obviously guided by the northward movement of the parent storm, this tornado moved north-northwest, directly towards us. Thankfully we were about 5 - 6 miles away from it upon first sighting, so we had some time to watch it approach. As it continued to near us, I filmed it while holding the driver's side door open against 30 kt inflow/north winds. I was looking all around the environment in utter disbelief that this was happening when I saw something alarming: a second tornado(2) - multi-vortex - had just touched down probably about 1 mile to our southeast! It was also moving in our general direction (although not directly at us). I alerted other group members and we took off north to try to stay ahead of it.
Unfortunately, the second tornado was moving too fast for us to get back up to highway 20 and east, so we had to keep going north on highway 73. The environment continued to bewilder us as a fairly dense fog set in, reducing visibility to well under one mile, and maybe as low as one-quarter mile at times. It was rather disconcerting knowing there were two tornadoes moving towards us as we fled north. Essentially, we couldn't see anything. To stay safe we kept blasting north for miles. Just north of where highway 20 turned to the west again, we found a road that looked like it went far enough east for us to get out of the way. The road was rain soaked dirt, so we could only go east at about 35 mph, and even that was very tricky.
Apparently our eastward movement was enough to get us out of the way, as other team members coming up from the south confirmed that both tornadoes had lifted as they crossed our latitude. Thus we went back to highway 73 and continued north. Although I can't confirm seeing any additional tornadoes along the stretch of road up to Lemmon, I did see inflow from very low clouds streaming to the west just a few hundred feet over our heads for quite a bit of the drive. We also saw numerous suspicious cloud formations/rotation which started making us think almost any low hanging cloud tag could be tornadic.
Did I mention that radar data through this stretch had become horrible due to the poor data coverage and the fact that the Bismarck, ND radar was down, leaving us with only the Rapid City radar, away from which we were by more than 100 miles? The conditions were so poor for determining what was going on.
We fueled up in Lemmon while the city was under a tornado warning, yet there were no sirens blaring and it felt more like a gloomy fall day (the dense fog was off and on during this stretch, but was very dense in Lemmon at this time) than the very dangerous scenario that it was. We were warning locals who came up to talk to us.
The most dangerous part of the storm appeared to stay west of town, so in curiosity, we ventured back out to highway 73 and south a few miles. By this time, the storm(s) that had produced so many tornadoes had now moved northwest into North Dakota. All we saw the second time around was cold westerly winds. At least the fog had lifted so we could see a few miles around us...
Seeing nothing, we returned to Lemmon and continued east on highway 73/12 when we burst back into the light as we recrossed the cold front. We were immediately greeted with very warm and moist conditions, as well as very strong winds from the south-southeast! Radar data suggested we take a peek into North Dakota to see what there was. This would be my first time in North Dakota, and it was an experience I'll never forget...
We had made it far enough east to see the structure of the storms, which had taken on a shelf cloud appearance as if they were organizing into a squall line. The outflow boundary of the squall line seemed to be coincident with the cold front. We traveled few miles north into North Dakota on state highway 49 when suddenly a vortex popped out of the leading edge of the shelf and touched down, becoming a ghostly white needle tornado(3)! This tornado was not born of a mesocyclone that I was aware of, rather it seemed to form due to incredible intense shear along the edge of the storm. The thermodynamic gradient and wind shear in the low levels was very strong here, so it probably didn't take much for a low-level updraft to quickly tilt and stretch some of the vorticity (surface vorticity, a known ingredient for causing such tornadoes) formed by the strong low-level shear into a tornado. Although SBCAPE was rather low in this location at this time, MUCAPE was much higher suggesting some strong instability based just above the surface. There was plenty of lift in the area from the cold front, so surface based activity had a logical reason to continue.
Anyway, we stopped to watch it, but the tornado was brief and I was unable to get any video of it. However, the shear zone from which it was born persisted for several minutes. As we sat there watching it and waiting for it to put down another one, part of the line to our south began to surge. Thus, within a few minutes, we had a shelf cloud and wall of rain coming at us from the southwest and south. It was moving over the road behind us, so our only option was to keep going north.
Things got really hairy after we began moving. The line started surging quickly, so even as we accelerated to 70 - 80 mph, we were not making any progress ahead of it. That's when random tornadoes started touching down all over the place. Just like when we were on highway 73 south of Lemmon, I don't know how many tornadoes touched down during this stretch, but I'll tell of those I did see for sure:
There were numerous areas of rotation along the leading edge of the shelf cloud. I had to pay attention to these while driving, as the angle of motion of the shelf and the road kept us moving right under each one. At one point, some sort of shed or agricultural building a few hundred yards to the west of the highway began to fly apart as a plume of dust flew up around it, indicating a likely tornado(4), although no funnel was visible. I recall seeing another splash of dust/vapor as this circulation moved over a small pond just west of the road as we passed it. Then tumbleweeds began to fly across the road from southwest to northeast. Then, right in front of my eyes, they turned to the north, then the northwest, right in front of me! Being forced north by the now wall of death just behind me, I had to keep driving, and as I drove through this circulation, I felt the car jerk to the right, then left. I managed to stay on the road.
A few moments later, I looked into my rear-view mirror and saw another tornado(5) already on the ground to the east of the highway! It looked nearly identical to the one we saw that first prompted us to stop a few minutes ago. Then I looked up and saw yet another area of rotation along the edge of the shelf. It was on a path that would take us directly under it as it crossed the road. I didn't even have time to think about it when Carl cried on the radio, "10 o'clock!" Even though that's where I was already looking (towards the rotation just ahead of and above us), another ghostly, white, needle tornado(6) had just touched down behind the threat area I was viewing! It all became too much for me to handle, so I did what I had to to avoid the circulation just in front of me: I stopped.
The circulation passed over the road without putting down a tornado. Before I could get moving again, a sudden gust of wind hit us from the west. It brought heavy rain with it. The winds quickly accelerated further and approached severe limits sustained, with higher gusts, hitting the car broadside. I decided for safety from the winds to turn broadside on the road so that the car faced the wind. Just after I did that, Chris pointed up the road at yet another tornado(7), this one broad and multiple vortex, that was in progress! We lost visibility shortly after that as the strong winds continued. I'm guessing this was either some sort of RFD (even though I don't think the storm was a supercell) or just the winds from the squall line. I was careful to watch down both sides of the road to make sure no other cars (only one came by and I let him through as we were part of the same group...) came by and hit us. Just like Bill Paxton in Twister, "Nobody will be there," is what I thought. Anyone dumb enough to be on this road here at this time had bigger worries than me, so I was confident in the low likelihood that someone might fly over the hill at 60 mph and smack us. No one did.
The group got separated during this chain of events. Chris, Tony, Ed, and I ended up together and aborted the mission/chase at that point. We started heading back into South Dakota.
We were going to stay in Spearfish for the night, so we headed back down highway 73 where our first tornado encounters of the day had taken place. On our way by the highway 20 eastbound intersection, we saw damage. A schoolhouse, along with an RWIS station, had been hit by one of the first two tornadoes we saw (I think the second one). This tornado ended up being rated EF-2 due to the damage it did to that school. It ripped the roof clean off and knocked several walls down. Some of the roof and walls were found a few hundred yards away in a field. The only walls that remained were interior walls. The basement was fine, too, other than having some water running down into it. This school was a prime example of why interior rooms or the basement are the safest places to be in a single building like that when a tornado strikes - those areas were the only areas left standing! One person got a video of the school being hit and put it on YouTube: http://www.youtube.com/watch?v=RVQL5DcO9ok. Here's what that school looked like afterward: http://www.youtube.com/watch?v=b_i2M2fygu4.
The drive to Spearfish was very desolate. Further more, as a hint, don't wander into this area of South Dakota low on fuel because there are very few fuel stops along the way.
What an amazing three days in South Dakota and what a welcome to North Dakota!
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