June 17, 2014

Jennifer Brindley, Phil Bates, and I were on day eight of a plains run and still recovering from the previous day’s chase. Another volatile event was setting up in the same Siouxland corner with a warm front draped from the WY/NE/SD corner across northern Iowa, backed surface winds, and decent westerlies aloft. Very rich moisture and strong heating would lead to another day of strong to extreme instability, and coupled with favorable speed and directional shear we had the potential for more supercells and tornadoes. The Storm Prediction Center favored areas to the east down the warm front where the low level jet was a bit stronger and areas way out west where upslope lift would yield greater storm coverage. We held our ground, noting what appeared to be a convergence point on the forecast models and visible satellite that would probably interact with remnant outflow boundaries from the overnight MCS. We expected storms to fire near Sioux City and hopefully move east of populated areas. We targeted an area just downstream, near Moville, Iowa where I had seen an F4 wedge just a few months earlier.

We slept in and had a leisurely departure from our hotel in Sioux City before heading over to Red Robin for some lunch. What The Duck chilling on a camera strap hammock under the camera dome:

We were in Moville by early afternoon and hanging out on a nearby hill under sunny skies with small white cumulus. The air was hot and sticky. We headed over to Subway to stock up on food before our chase started. Brindley and I engage in sparring matches during sandwich creation. It’s a chase tradition.

By early evening we still had no sign of storm initiation. We drifted northwest of town and found a scenic overlook that provided views of the countryside and gorgeous sky with rays of sun poking through clouds layers in the soupy air near the warm front. Skip Talbot, professional sunbeam chaser:

Phil Bates shoots time lapse of the cloud layers and sunbeams with his Red.

Evening wore on and we saw a patch of more robust cumulus developing in the northeast corner of Nebraska on visible satellite. That was our area of convergence that would spawn our storm. The high resolution model's plot of rotating storm tracks showed a maxed out point on the map, rather than a line segment track. I thought it was some sort of error when I saw it initially, but in hindsight the HRRR had nailed the updraft helicity track of a stationary storm. Initiation appeared imminent so we started tracking back west for the intercept, heading south of Sioux City into Nebraska on highway 20. Storm motion was initially to the northeast and the tiny updrafts were only miles from the Missouri River. I anticipated getting on the storm before it was mature, and then falling behind at the Vermillion, South Dakota river crossing and playing catch up as we maneuvered through town and back into position in South Dakota. Rather than deal with that situation and miss the show while out of position, I decided we better get in front of the storm and wait for it on the other side of the river. I turned us around and we headed back through Sioux City and into South Dakota on I-29 before cutting west toward Vermillion.

We stopped a few miles shy of Vermillion, underneath the anvil of the developing storm. The updraft tower loomed in the distance, with streaming bands of cumulus feeding into it and rain falling from the forward flank against the golden evening light. Twenty miles back from the storm, there was only a light breeze. Frogs croaked and birds chirped against the distant rumbles of thunder while we waited in the farmlands of southeast South Dakota, saturated with water from the previous days’ storms. Phil and I shot some time lapse of the updraft tower, but after a few minutes it became obvious that I misjudged the storm motion, and the forward speed of the storm had nearly halted while it rapidly matured. We were way too far down stream and would have to make a mad dash to get closer for the intercept. We packed it up and headed toward Vermillion. I loathed the intercept. The Vermillion crossing is a bunch of zigzagging roads with slow speed limits. We would be seriously delayed getting underneath the updraft base. We weren’t the only ones that had erred on the storm motion. We spotted a few other cars pulled off on the sides of the road, still awaiting the storm as we raced into Vermillion.

After plodding through town and dashing across the river we were in Nebraska and moving toward the storm in the rain under the forward flank. The storm was now tornado warned and the first reports were starting to come in. Like the day before, we were missing the show. I had a paved route to the storm, but it involved a core punch. With a massive supercell now producing tornadoes and potentially huge hail, I decided that the route would take us too close to dangerous parts of the storm. We could drive into a rain wrapped tornado or have the windows smashed out by hail before we intercepted. I was also still anticipating some forward motion of the storm and tornado, but in hindsight we probably could have taken our faster, more direct paved route without issues. It’s better to be safe than sorry, and I’d much rather come in a couple minutes late than gamble our ride home or our lives. I pulled a U-turn and we headed south immediately on the unpaved grid.

The road twisted and turned and our progress was slow on the loose gravel. I turned us west when we were about even with the southern edge of the forward flank. Brindley strained to see the updraft base through the rain. The semi hilly terrain along the river obstructed our view at times. Topping one hill, the terrain opened up in front of us and we saw it: the updraft base looming out of the rain with the unmistakable silhouette of a wedge tornado underneath. Amazed yet eager to get a better view, we pushed on. The forward edge of the updraft base dipped low and for a while I thought we might have another dual mesocyclone like on the Pilger storm the day before, or at least a mesocyclone hand off.

We ran west down gravel until we hit our originally planned north south paved road. The wedge sat a few miles to the west still, apparently frozen in place. Our contrast improved dramatically but we still had some nagging rain. There was some debate about stopping to get the shot or continuing on to a spot clear of the rain.

We opted to head a couple miles south, and found a small hill with an amazing vantage point. The wedge tornado towered above the landscape and loomed on the horizon like an epic monster. Tendrils of bear’s cage precipitation danced around it, and the white cloud mass of the mesocyclone above turned slowly.

An ultra-wide shot from the video shows the tornado framed by dramatic and textbook supercell structure, the sculpted updraft tower extending thousands of feet into the vault. We got out of the van in awe, methodically working our cameras. I often wish we could have positioned ourselves on the storm earlier and gotten a lot closer, but we still had a sight to behold and a shot that was made so much more amazing by the structure in which it was framed.

Another wide shot showing the rear flanking gust front extending to the south and the thick band of inflow above feeding into the updraft tower:

A couple of cars, probably local residents, appeared to be darting east away from the tornado. I zoomed in with the video. The cars looked tiny against the huge, looming beast on the horizon.

Rain bands of the bear’s cage spiraled around the wedge, the edges churned and boiled with violent motion. The tornado’s forward speed appeared quite slow, however.

We watched the tornado for several minutes. The rain never cleared, but was instead coming down heavier and small hail was starting to ping off the van. We were getting quite wet standing outside, Phil trying to duck under the open hatchback. To my disappointment the tornado started to become engulfed in rain. We remained hopeful that a dry rear flanking downdraft would clean the rain out, but the high contrast wedge rope out would elude us. We held our ground until the lip of the mesocyclone and spiraling rain bands marking the edge of the bear’s cage was almost overhead. With the violent, rain wrapped wedge and poor visibility and dangerous winds inside the bear’s cage approaching, it was time to take our escape route. The tornado’s motion was so slow it appeared to be nearly stationary, but after watching it for minutes we could see that it was drifting to our left and was moving south of us. There was clear air and blue skies just a few miles to our south and the tornado still appeared to be a couple miles off. However, El Reno taught us to never cross the path of a tornado or a tornado producing region when escaping. The bear’s cage region was several miles across. We likely wouldn’t clear it heading south and would get slammed by severe RFD or potentially a rain wrapped satellite tornado. Or even worse, and like El Reno, a surge in the RFD could send a rapidly expanding wedge tornado careening at high speed into us while we raced it across its path. We were going north to escape and given the magnitude of the tornado, the supercell, and the environmental instability, I expected that we would encounter huge hail as a result, but it was the lesser of two evils.

We packed up our cameras up and drove north. The size of the hail picked up quickly and I prepared Brindley and Phil to be ready if we lost glass. The hail didn’t get much larger than half dollars though and then we were back in the heavy rain of the forward flank. We turned east on the same gravel road we came in on and started putting ground between us and the mesocyclone. The nearly stationary storm had dumped a ton of rain and what had been a firm, well compacted road was now a sloppy mess. The van’s tires clawed for traction as we drove up hills in the driving rain. We stopped atop one after a few miles to see if the visibility to our southwest would improve with time and perhaps we’d regain sight of the updraft base. While we waited and checked radar, a vehicle heading toward the storm approached and stopped by us. They were chasers and looking for a view of the storm. I told them there was a rain wrapped, potentially violent tornado and that unless they were experienced they should turn around and head north. After a few moments they did indeed turn around. The pouring rain was compromising all the gridded roads around us and we had zero visibility at this point so we decided to pull the plug on the chase and bail north back through Vermillion and away from the storm.

It was dusk by the time we got up to Vermillion. The supercell filled the southern sky, but clear skies and twilight lit it from the west. Bolts were shooting out from the forward flank and anvil and we decided to stop and shoot lightning. We drove a few miles west of town to a remote spot and setup our tripods. A small cell underneath the anvil went up, lit blue by twilight. Purples anvil crawlers raked along underneath and lit up the rain core in shades of orange. The sight was so beautiful it made me forget about the swarms of mosquitos that had descended on us when we stopped. We shot lightning until the storm started to sputter and then headed east to 29 to make for Minneapolis and our room for the night.

By nightfall storms started to fire all across the warm sector. A supercell went up west of Sioux Falls, developed a hook and went tornado warned. The couplet on the storm looked impressive. It was likely producing a tornado. We were tired and had a long drive ahead of us, and spotting the tornado after dark would be difficult, but it was so close, a mere 20 miles away. Brindley wanted to let it go, but this was our last chance of the trip, and I wanted to make the most of it. I tried to talk Phil and Brindley into the intercept. They weren’t convinced but I decided to go for it anyway and turned the van down I-90 west for the intercept. The storm was sitting just north of the highway, but the forward flank had a lobe extending across the highway. Rain hammered down as we merged onto the highway. The tornado was miles to our west on the backend of the storm, shrouded in darkness and the miles of precipitation between us and it. The highway was eerily deserted and the sky inky black. The rain intensified and then the hail started. To my bemusement and disappointment, the couplet on the velocity scans started moving rapidly to the west. It was very uncharacteristic tornado behavior, but it also meant it was just getting further and further away from us and into the precipitation. By this point Brindley was visibly flustered that I was pushing us into dangerous conditions. With still no visibility, I agreed I was being foolish and abandoned the intercept. I turned us around at the next exit, the couplet dissipating and still miles to the west. We made the trek down 90 east between dozens of storm cells tracking across the southern Minnesota. The sky was alive with electricity. We got a few short hours of sleep, said our farewells to Phil early the next morning and started our long trek home, ending an amazing week in the northern plains.