June 12th, 2017 High Plains Tornado Machine

Tornadoes: 8

Largest Hail: ~2.75"

Highest winds: nothing notable, < 40 mph

June 12th was a big day that we highly anticipated over the previous week or so. I had May 20th to the end of June free to chase, and there had been almost no action in the Plains in that time frame up until that point. It was an utterly disappointing time for peak season in Tornado Alley. However, models began to pick up on a western trough developing and bringing with it sufficient flow and thermodynamics for a string of severe weather days sometime in the June 10-15th time frame. Models really liked the Black Hills into the High Plains several days out. Knowing what had happened nearly the entire season prior, however, I was afraid the system would have a fatal flaw (or ten) that rendered it worthless. It held steady, though, and by the 9th or so we were seriously planning on a trip out. Matt Magiera, Isaac Polanski, Paul Sieczka, Sam Bertellotti, and I decided to leave early in the morning of the 11th, as there appeared to be a supercell play from SW Nebraska into SE Wyoming and NE Colorado. We didn't end up actually chasing that day, so I'm lumping it in here. Our two-vehicle caravan arrived in Cheyenne after a long 14 hour drive and spent the night messing around, exploring, and doing some astrophotography:

We also performed a ritual to the SPC gods hoping for some good luck:

A bowling ball upper low was barreling in from the west, with favorable mid to upper level flow streaming in across the northern High Plains. Underneath, a surface low was expected to form on the lee side of the mountains, with a healthy low level wind field response out of the southeast. This southeasterly flow would also act to advect some very impressive dewpoints for the High Plains, up into the 60s. Storms would likely erupt on the mountains due to the upslope flow, then move out into the plains where they could go nuts.

NAM forecast sounding from southeastern Wyoming the night before. One of the most impressive forecast soundings I can remember:

Very steep lapse rates, impressive directional shear, lots of instability, particularly in the low levels, gorgeous hodograph, favorable LCLs...it appeared a significant tornado event was set to unfold. Waking up in the morning, we were greeted with a thick blanket of fog from our hotel. We were also greeted with a doozy of an SPC outlook, one that featured the furthest west 15% tornado risk they've ever issued:

After a while, we all got up and went to the lobby where we could eat breakfast and look over data. It still looked impressive, but trends began to diverge on location of the highest threat. Many high-res models were splitting from their east-central/SE Wyoming solutions, instead favoring further south into Colorado. We were also beginning to become concerned with the potential for storms further north towards Chugwater to become messy, creating less-than-favorable storm interference for tornadoes. The cap was a bit stronger further south, though, as seen by a sounding taken by the COD chase group from Fort Morgan, CO at 17z:

At the same time, the HRRR was consistently depicting the same storm/group of cells forming in NE Colorado, then heading northeast into SE WY and W NE with a solid, intense UDH track. The HRRR may be sort of a meme for chasers, but whenever it's dead-set on a particular storm across multiple runs, you pay attention. In the meantime, we decided to stay in Cheyenne to wait for further trends to make a final decision. We found an amazing overlook on the southwest side of town just off I-25. A cu field started to form:

Around the same time, a Tornado Watch was issued. To our surprise, it was a PDS watch with 90/80 probs, the highest probability Tornado Watch I've been in in my life (even those issued on November 17th, 2013 were lower):

Finally, after discussing amongst ourselves and a few other chasers who were parked nearby, we committed to the southern target. Storms were starting to go up to the north, but we started heading south down I-25 into Colorado as we noticed cumulus towers gaining some appreciable height. Echoes began erupting off the mountains, and we gained visual on some bases. One in particular stood out, and we found some back roads off the interstate to watch them mature a little. Sitting around for a bit, our storm was beginning to gain some supercell characteristics on radar, and another not-yet-remarkable but storm worth watching formed 5-10 miles to our south. We were still playing the waiting game to see if the southern cell would just get ingested into our storm, or if it too would become a supercell, choking the northern one off.

Waiting for developing storms to mature:

The southern cell began to exhibit supercell characteristics too, but it was still not mature, and our storm was beginning to reach maturity with enough space still between the two storms to not worry about interference. Ours now had a wall cloud and some impressive structure in its meso:

Our storm cycled a time or two before the southern cell began to also become a mature supercell that was raining into the northern one. Or it would have been if there was actually any rain in it. Looking due south, we were able to see the entire updraft of the southern cell through its core. It didn't take long for us to figure out why. The entire core was massive hail, no liquid whatsoever.

And only a few minutes later, wanting to drop onto that storm, we experienced the core firsthand. We were forced to stop just north of Pierce as baseballs were flying. This was my first experience with mega-hail. I've seen some quarters to golf balls before, but nothing where I was just waiting for a window to explode. I was pretty afraid, as embarrassing as that may be to admit. I put someone's backpack against the window so that I wouldn't be showered with glass if it broke. Only one massive stone ended up hitting glass, thankfully, and it struck the windshield wiper as it moved across, leaving a sizable dent in it. When the hail subsided, we got out to sample some:

We headed back on the pursuit, with several cycles of the storm that produced nothing. Structure was awesome at times, but motion was lackluster, and I was beginning to get nervous at this point that we were going to bust. Putting even more pressure on, a storm about 50 miles to our north near Cheyenne had just produced a gorgeous tornado that images of were pouring in on social media. I made the observation that LCL heights were likely too high to support much tornado threat as far south as we were, and blamed that solely at the time. Looking back, I do think our storm was in less favorable moisture, and LCLs were a problem at that time, but dynamics were probably not quite there yet. The aforementioned Cheyenne tornado was likely a sign the better dynamics were arriving. And literally the next cycle on our storm was when the fun stuff started. The storm likely moved into a bit better moisture as the bases lowered quite dramatically in a matter of minutes. A huge, blocky, white wall cloud formed with turbulent motion underneath it. A few minutes later, a thin snaky rope materialized underneath. After going on 2 hours with 2 different storms, we finally had a tornado:

The tornado quickly morphed into a fat white cone under a blocky wall cloud, a dream shot if only we were closer and had a bit better contrast:

It morphed into a bit fatter cone before starting a long occlusion process that lasted the majority of its life cycle. We raced north to get a closer look at it:

We initially thought it was going to completely rope out, but about 5-7 minutes later, it had started to thicken up again into more of an elephant trunk. Still racing northward, and the tornado still widening, we came across a farmstead that took a direct impact. A barn was flattened, house (thankfully) lightly damaged, power lines down across the road, and an audible gas leak. A bit concerned with the gas being ignited by the downed power lines, we went through the ditch around the downed lines to get away and press closer to the tornado:

After the downed lines, we caught up to the rest of the chasers towards a 90 degree curve in the road. Passing a semi that was pulled over (which had been closer to the tornado than any chaser video I've seen since), we finally stopped about a quarter mile behind the tornado. Sheet metal was flying through the air and hail turned the field white. This was the most dramatic tornado encounter of my life so far:

The tornado then began a dramatic ropeout:

Video:

Completely pumped with adrenaline by the time the tornado dissipated, we continued in pursuit of the storm. Heading down a dirt road eastbound, we saw what we were pretty sure was a tornado, but not positive. It was a small funnel with a dust cloud underneath it. At 2018 Chasercon, Tim Marshall confirmed this as a brief anticyclonic tornado:

We made it onto I-80 as we fell decently behind the storm on the somewhat lackluster road grid now in far southeast Wyoming. Here, we witnessed an incredibly turbulent updraft region with numerous transient funnels forming and dissipating. At one point, small cyclonic and anticyclonic funnels formed together into a ring, something I had only seen in an old home video (if you're really into storms you'll know which one I'm talking about). The supercell also had incredible UFO structure when we finally got ahead of it:

At this point, we now had two separate, distinct mesocyclones. We stayed between the two of them to have a good vantage point if either wanted to produce. Sirens were blaring in the town of Bushnell, NE as rotation really picked up in the western meso. We headed out of town, stopping in a scenic location with some beautiful grassy hills. After a few minutes of sitting there, a funnel began to drop as the eastern meso was churning away rapidly. The funnel touched down, and given the motion in the eastern circulation, we were sure we'd have dual tornadoes very soon. The Piotrowskis pulled up a minute later, much to our surprise, and Jeff stated the same thing. The eastern wall cloud, which was just to our north, kept spinning hard with nothing making it to the ground. The tornado a couple miles to our west, however, was beautiful:

A couple minutes later, the tornado started to rope out. Notice, though, the new mesocyclone forming to its west. There were now three mesos worth watching for tornado production. We were a bit at a loss for words as to what we were witnessing.

Another 5 minutes or so later, a funnel began descending from the western circulation. Another stout tornado:

Given a little time, it too roped out. My camera batteries were threatening to go dead with the storms still going strong. We kept going, the storm spitting out a few more brief tornadoes, including another anticyclonic that tore through a construction zone, leaving a mess of traffic cones and power lines in its wake:

Final brief tornado:

After one last funnel that reached about a third of the way down, we decided to let the storm go. It was still producing tornadoes, but they were getting embedded deeply in rain, and we'd seen more than our share of tornadoes. We started looking for hotels, and a little while later stopped by some buildings in the middle of nowhere to celebrate our victory with Paul and Sam. A group of teenagers came out of one of the buildings, apparently part of a youth church group, talking about the storms that just missed them. We showed them some of our shots from the day, and they were all pretty in awe. It was fun to meet up with some of the locals who showed interest in what we were doing.

Overall...what a day. My best storm chase by far. I only wish I'd not turned off image stabilization on my camcorder because I (wrongly) thought you could only use manual focus without it on. There's always next time. I think it'll be a while until there's a next time like this, but it's all a learning experience.

SPC Storm Reports:

A full-fledged tornado outbreak across the High Plains.