April 9, 2011


Initial Target: Missouri Valley, IA
Departure: Westchester, IL 7:00 am CDT
Arrival: Fort Dodge, IA 12:30 am CDT
Intercepts: Mapleton, IA, Kiron, IA, Sac City, IA
Tornadoes: 6
Hail: Severe (1.5 inch estimated)
Wind: Severe (53 knots measured [courtesy Jeff Duda])
Features: Tornado, Gustnado, RFD Gust Front
Miles: 598


Dryline/warmfront play across northwest IA. Targeted Omaha area for evening initiation of supercells. Stopped in Missouri Valley, IA to follow building cumulus to northwest. North moving cell initiated in northwest NE but turned right and moved into the warm sector in Iowa. Intercepted cell near Hornick, IA noting rain free base. Storm went tornado warned with reported tornado so dropped south between RFD clear slot and precipitation core noting outflow/gustnado/tornado combination debris cloud underneath. Moved east toward Mapleton as large barrel shaped tornado formed and moved into town before becoming rain wrapped, occluding and exiting north side of town. Drove north end of Mapleton noting minor roof and tree damage. Got ahead of storm just before dark noting large, striated HP supercell structure. Observed several tornadoes after dark between the cities of Kiron and Sac City, IA, from several miles south of the storm, backlit by lightning. Shot some lightning stills before heading to Fort Dodge for dinner and room.


Crew and Equipment:

Chase partners: Mike Boik, Jennifer Brindley.  Equipment:  Kenwood TH-F6A Tribander, Dell Inspiron Laptop.  Millenicom 760 USB datacard and cradlepoint router, Holux 236 GPS, Robotic camera dome with Sony XR-520V. Canon 60D and EF-S 10-22mm

Photography courtesy: Jennifer Brindley


Courtesy Mike Boik: http://www.youtube.com/watch?v=Qx0rP2Hc-So


Saturday, April 9, was shaping up to be the best setup of the year (although this wasn't saying much as the season had barely begun). A 100 knot jetstreak was rounding the base of trough which was moving out of the Rockies. Favorable 50-60 knot 500 mb winds were forecast to overtake the Plains by evening providing lift across a dryline extending south from Omaha and a warm front arcing up over northern Iowa. A compact surface low and strong low level jet would provide ample directional shear with surface winds backing nicely across much of the warm sector. Dewpoints into the mid 60's and temperatures in the low 80's would also strongly destabilize the warm sector with surface based CAPE forecast at 3000-4000 J/kg.

However, the big uncertainy with the forecast resided with the cap. The best upper level dynamics and forcing from the trough were still well to the west. The cold air aloft that would further destabilize the atmosphere and erode the inhibition was also further west with the trough. Would storms initiate early enough to get a chase in the daylight? Would they wait until dark when the low level jet kicked in? Would they fail to initiate at all as the cap was forecast to fill back in overnight? Half the numerical models said we'd be seeing storms near the dryline/warm front intersection by early evening. The other half said it would be after dark further up the warm front. The helicity was very high on the warm front, however, and coupled with the strong instability, tornado parameters were almost off the charts for much of western Iowa. The numbers were just too good to pass up. Daylight initiation or not, I was chasing this setup.

I was prepared to chase solo, but got a couple last minute chase partner requests: Mike Boik, a newer chaser on the scene from Streator, IL, whom I'd met at the Weather Festival last fall, and Jenn Brindley, a professional photographer from Milwaukee whom I had met a couple weeks earlier on the Creston, IA chase while she was chasing with Tony Laubach. We agreed to meet up at the Dekalb oasis for a two day marathon chase out to western Iowa and back. We assembled at the oasis at 8 am, and after finding out we couldn't leave the cars there overnight, took a short detour to a Wal-Mart in town to drop the cars, and we were off.

I had been eyeing the warm front much further east than the advertised tornado parameters indicated. Several times I had been lured to western Iowa or further just to see the warm front in Illinois light up with supercells. We needed some good overnight storms to put down some outflow boundaries for afternoon initiation on Saturday, but as we left for the chase, there was just thick fog and stratus north of the warm front and completely clear skies south of the warm front. The warm front looked like it would stay largely capped. The other secondary target was the dryline down into Kansas. Initially, the dryline looked like the more favorable play with more discrete storms over the best terrain. However, as the trough slowed down, the advertised capping indicated a slim chance for surface based initiation. In addition, the 20-30 degree temp/dewpoint spreads in this area would lead to very high storm bases, less likely to produce tornadoes. So by Saturday morning, the dryline-warmfront triple point near Sioux City and points to the southeast looked like the obvious target. The RUC and HRRR were both indicating initiation near Omaha by 7pm, so the plan was to hang out just east of Omaha on the Iowa side and catch the storms once they had crossed the Missouri river.

We made great time heading west making it to I-29 by early afternoon. I wanted to stop in Missouri Valley, IA to get lunch and wait for initiation. Mike and Jenn wanted to buy tripods, however, and I figured we had a few hours to kill yet so we headed down to Council Bluffs and hit up a Best Buy and Applebee's for lunch where we were soon joined by Jesse Risley, Brad Goddard, and Jodi Irvin-Dewispelaere. Afterwards, we moved to a bank and met James Seitz, Robert Hurkes, Nick Nolte, several other chasers, and a guy on a bicycle who was missing most of his teeth, wearing a coat in 80 degree weather, and was just enthralled to see us.

After getting a demo of the biker guy's walkman and some bicycle oriented directions on how to get back to 29, we decided to head up 29 to Missouri Valley. A band of cumulus was going up in eastern Nebraska becoming more robust. As it drifted northeast, we'd have to move north as well to keep up with it.

Now in Missouri Valley, each time we stopped we were greeted by larger and larger chaser convergences. The truck stop lot at Missouri Valley was almost filled with chasers including several from the TVN crew and greatly respected chase veterans Jon and Shawna Davies. We didn't wait around too long. At around 5 pm, the northern end of the cumulus band initiated and a small cell started showing returns on doppler reflectivity. The cell, northwest of us, was moving very fast to the north. We watched it for a couple of scans and I figured that this wasn't our storm. The cell would quickly outrun the warm front, and we'd also be in a tough position trying to catch it given the northerly component.

Still, the cell started to blow up into a storm and was turning on a more northeasterly course. Meanwhile, the cumulus line extending to the south was not initiating, an area where I had expected more storms to develop. The parking lot started to clear out, and I got real anxious watching the radar and decided we better make a play on that storm. We could always drop back down south as we'd be downstream from other storms that might go up. As we pulled out of the lot I shouted to Nick Nolte, "We're getting suckered north!"
As the storm became rooted to the surface it turned more and more to the right and continued to strengthen. To the east in northwest Iowa, the warm front bowed all the way up to the Minnesota border. As I checked the surface observations and visible satellite, I realized that this storm would stay in the strongly destabilized environment and the directional shear would continue to increase as the evening approached. I was becoming more and more confident this was our storm.
We went north up I-29 with Brad, Jesse, and Jodi behind us as the anvil, flanking line, and the base started to come into view. The storm picked up a severe thunderstorm warning and we were gaining on it rapidly. The Whiting exit looked like a good place to exit 29 and let the storm track to us while it matured, providing us a nice view from the clear air to the southwest. The exit was closed due to construction, however, so we had go up to the next exit, which was highway 141.

This put us north of the storm and in the path of the precipitation core, but I figured there was plenty of time to use local roads to drop back south if we needed to. We headed east down 141 past Hornick and then stopped, waiting for the storm to move northeast up to us. We didn't have much of a view of the base at this point, but the roads to our southeast were terrible so I figured we better just hold our ground.

The storm was not really cooperating, however, and continued to build to the south such that the base would never make it up to us. Brad's crew followed us as we turned back onto 141 and started heading east, making for the next south option which bent back to the southwest. That's when the tornado warning came in. It couldn't wait until we were in the perfect position with a nice view of the base. Instead it was while we were in an awkward position, well downstream from the storm, with no good way to immediately intercept. I was biting my nails trying to decide whether to continue driving the 3-4 miles to the next south highway, knowing we'd have to drive back west a couple miles to intercept, or to turn around now and make for the county road south out of Hornick which was more direct, but would require a core punch and us possibly coming out behind the storm. Chris Heater, a rookie chaser from Illinois, reported a tornado in progress. We'd have to intercept now. I got on the radio saying I was turning around, but Brad's crew had already done so. I swung the van around and blasted back west down 141. The move seemed erratic, and the route into the storm, risky. Mike was concerned and questioned the tactic, I tried to convey my reasoning, silently hoping we wouldn't wind up stuck in the core, or fall behind the storm. Jesse Risley's voice crackled over the radio cutting in and out with static, "----uge tornado! -----" My heart raced as we gunned it down the road trying to make it in time for the intercept.
Craning my neck to the left I could see a large dust plume to our south. That had to be the tornado I exclaimed, and yet the more I watched it, the more it appeared like rear flanking downdraft outflow. We finally made it to County K64 and blasted south into the storm. Our view was obscured as we were now looking through most of the core. Mike's concern grew as we blasted into the core.
We headed east down country road E16 and came out from under the core of the storm with a large horseshoe shaped updraft base immediately in front of us, cut deep with a rear flanking downdraft clear slot. Immediately obvious were large dust plumes to our south. Inside the clear slot, the clouds churned like a boiling cauldron. I scoured the updraft base above us looking for a funnel or tight rotation to associate with the plumes on the ground, but couldn't make any out. Our attention turned to the dust plumes in front of us. Some took on a nice bowl shape, appearing almost tornadic, but then another smaller plume would appear nearby, suggesting gustnado activity. Then more linear looking outflow would sweep by. Unable to associate rotation aloft with the features, I could only speculate as to whether it was tornado, gustnado, or RFD. Collaborating with other chasers afterwards, however, some chasers did get shots of a funnel above the circulations, so it was probable that all three phenomena were ongoing during this time.



Unfortunately, the pan motor on the camera dome stopped working, probably due to a loose connection or a wire entanglement. Hail stones about an inch and half were falling so I didn't really have an opportunity to try and get out and fix it, nor would I for the duration of our daylight chase. Luckily Mike was shooting video and Jenn was taking stills so the chase was still well documented.

Overhead, the northwest corner of the horseshoe updraft base was curling with some rather dramatic rotation. Mike, visibly uneasy, did not want to be underneath the feature (and with good reason) and wanted us to backup. I put the van in reverse and we headed down the road a few yards. The move didn't really change our position on the storm, but I knew the storm was pretty much past us as it continued to move east. The base looked like it was starting to occlude, losing some of its structure with more and more rain starting to fall through the updraft base.

We'd have to move east to keep up with the storm and maintain our view. Staying just north of the hook and just south of the forward flank, we'd maintain our visual on the storm even if it transitioned into an HP mode. Unfortunately E16 turned into the classic Twister cliché: "Bob's Road" with varying, unpaved road quality, twists, and turns, hills and trees. We were in and out of the core of the storm. We'd get a peak of the storm's base every now and then. At one point we saw dark bands extending down from the apex of the horseshoe base. They could have been mistaken for a tornado, but the translucency made it appear more like the rain bands of a downdraft. I took the road as fast it would allow. There were big ruts that would pull me in different directions, and I was sliding a bit on some loose gravel. Miraculously, we were able to keep up with the storm, walking the fine line between big hail to the north and the tornado producing region of the storm to the south.

As we approached Mapleton from the northwest, I meant to take a more direct route to get back on pavement, but instead missed a turn and went southeast toward the town. The terrain didn't give us much of a view, until we rounded a bend and came out from the hills. Just to our southeast a large swirling debris cloud suddenly appeared. I slowed the van as we took in the sight. It was a tornado, and a large one too.

With the lack of foreground reference it was hard to gauge the size and distance of the tornado. It looked like it could still be a mile away, but at that distance the tornado itself would have to be over a half mile wide itself. "It's moving toward us!" Boik exclaimed. We were looking southeast at a tornado moving east, so I knew it wasn't approaching us. Instead it looked like it was getting larger.

An old white beater with a bunch of guys in it pulled up along side of us asking which way it was going. I hopped out and told them we were fine as it was moving away. At our position there was a mix of rain and hail so I wasn't able to fix the camera dome, and missed recording the tornado. Thankfully, Mike was able to get a pretty stable shot of the tornado with his camcorder and Jenn popped the sliding door open and got some gorgeous stills with her DSLR.

The tornado churned along as a big dusty debris cloud without much in the way of a visible condensation funnel above it. For only the third time since I started chasing, I could hear the sound of a tornado: a distant rushing sound as the barrel shape churned about three quarters of a mile away to our southeast. I glanced down at the mapping software and swore out loud. The direction in which we were watching the tornado and the direction to the town of Mapleton, IA lined up. The town was going to get hit. Given the size of the tornado, I feared that there would be widespread devastation. I paused to report the tornado on Spotter Network, but it had already been done, and the town had been warned well in advance. A power flash flared up on the leading edge of the tornado as it entered the town and exploded a transformer.


We watched the tornado for a few minutes, reassuring Mike that it wasn't going to get us, but our view was cut off as the precipitation in the hook of the storm caught up with us. We'd have to move east to get our view back, Mike reeling at the notion. We started down the gravel road toward the town of Mapleton. I paused to plan our route. Even though we couldn't see the tornado, its roar was much more audible now as it passed in front of us exiting the town to the north.

I knew there was going to be damage in Mapleton. The thought of it makes me sick to my stomach, and I have no training for dealing with such disasters, so I generally avoid damage scenes like the plague. It's not that I don't want to help those caught in the path, it's just that I would probably be more of a hinderance or wind up a victim myself. If we were going to keep chasing, however, our only path forward was through town as all the nearby roads converge on it. We proceeded cautiously. I rounded a bend to see a huge tractor barreling down the road right at us, the driver probably spooked by the tornado, and I had to swerve to miss him. We took 141 into the northwest side of town. The town was getting cored by rear flanking downdraft. Small pieces of debris were flying through the air, the sirens were wailing, and poles and wires were swaying in the wind. It was a surreal sight. We tried to find county road E16 that would lead us west out of town, but it wasn't clearly marked, and I had to turn us around a couple times before I found it. Meanwhile a whole string of vehicles, some of them most likely chasers, came in from the north and headed into town along with several emergency vehicles. Looking around we didn't see too much damage. There were some trees down and some minor roof and siding damage. Nothing looked too serious. I thought that perhaps the town had been largely spared by the tornado, or that, despite its size, was relatively weak. I saw no damage from my position that warranted a rescue effort. It wasn't until hours later that we learned that the southwest part of town had been hit the worst with significant damage. We found E16 and started down it, but there was a large tree down in the road a few blocks ahead blocking our path. Meanwhile, the storm was moving on and I could see clear air off to our west through the rain on the back end of the storm. I turned us down a side road to get around the tree on E16 while trying my best to avoid pieces of debris in the road. I hit a branch and it got caught in the wheel well, dragging along around the ground with a terrible noise. I hopped out quickly to yank it out and the white sedan, apparently still following us since the tornado touched down, pulled up along the side of us again. They said something but I was a little busy trying to get the branch out from under the van and assess how traversable the road was up ahead. Another tree was down ahead of us, but this one was smaller and ended by a driveway. We were able to drive up on the driveway and get around it. After a few blocks we were able to get back on E16 and were heading west out of town. We had cleared the tornado's damage path were back on the chase, unaware of the rescue operation underway on the south side of town.

We blasted down the highway to catch up with the storm that was sliding off to our northeast. Mike was pretty shook up after his first close encounter with a large tornado. Jenn and I did our best to try and calm him down, but I didn't want to abort the chase, so we'd play it safe for the rest of the chase and give the storm a wide berth. Jenn and Mike eventually switched seats as well so Mike could cool his nerves in the back.
We were able to get out several miles ahead of the storm before we went north on US 59 out of Schleswig. I put us right in front of the storm, which had turned into a massive, yet well sculpted HP supercell. In the last bit of twilight we could see some downdrafts inside of the rear flanking core of the storm but were unable to make out any tornadoes. The inflow winds into the storm were absolutely incredible. I only felt inflow like that on a chase once or twice in the past. Little bits of corn husk were flying through the air. Dirt and sand were getting kicked up in the winds as well. As the storm approached the winds went slack and then changed direction suggesting we were about to get some outflow. I thought the storm had gone elevated and outflow dominant, meaning the inflow was being pushed up over the storm's outflow and would no longer pose much of a tornado threat.
This was far from the case, however, as we would soon find out. We watched the storm until it got within a mile or two and the sky got completely dark, before we dropped south a few miles to an unpaved county road where we'd parallel the storm from the south. The lightning was really picking up and we stopped so Jenn could get some lightning shots. The lightning illuminated a huge mothership meso and the horseshoe shaped base underneath.
Jeff Duda and crew pulled up next to us and we shared stories from the chase as we watched the storm. Jeff had measured the inflow winds on the storm at 53 knots with his anemometer. Severe inflow, amazing!
A bowl started to form under the base. We got momentary glimpses of it as the lightning backlit. Everyone got excited as it looked like the storm was about to put down another tornado. Sure enough, a large cone started to form under the base and then touched down as a stovepipe shaped tornado. The inflow was incredible again and it changed direction to follow the tornado as the storm moved to the northeast. The storm was almost ten miles to our north, and with my camcorder tied up in the dome, and my still camera with only a wide angle lens, I let Mike and Jenn get shots of the storm and just relaxed taking in the sights.
The tornado lasted several minutes before roping out. The storm cycled, however, and a large bowl started to develop, this time with multiple point funnels dangling underneath. Powerflashes lit up the bottom of the tornado as lightning backlit it. I hopped on Spotter Network and reported it. There were lots of chasers and spotters on the storm reporting and the storm had been tornado warned for hours now, but I figured the update was a good idea.
The storm was not done producing yet and it was starting to get really far away, so we said farewell to Jeff and his crew and started stair stepping on a combination of paved and unpaved roads trying to catch back up with the storm. It was difficult to keep track of the tornadoes at this point as we couldn't tell where tornadoes were ending and others were beginning or if it was a continuation of the last one. At one point it looked like we had two large cone tornadoes on the ground, and then on the horizon to our northwest there appeared to be a large wedge. I hadn't seen such a dazzling array of nighttime tornadoes since March 28, 2007.
The wedge appeared to become heavily rain wrapped in the core of the storm and we lost our view of it in the darkness. We continued and stopped just north of Sac City to watch the lightning again and take in the structure. The supercell was developing photogenic striations and still had some great lightning, so Jenn set up to shoot some stills while I helped Mike upload his footage to our media broker, Kendra.
Blown away from an incredible chase, and even though there were still active tornado warnings, we decided to call it a night and head into town to get a room and some dinner if there was any place still open. We picked up a room at the Best Western in Fort Dodge and luckily the Applebee's was open until midnight so we got our celebratory steak dinner as well. We also met up with a couple of chasers who came all the way up from Texas to chase this event.

April 9 turned out to be an amazing chase despite initial concerns that we wouldn't get daytime initiation. When we did, and storms tracked into the warm sector, we quickly found ourselves on a multi-tornado supercell. The inititial gustnado activity wound up being a supercellular tornado as documented by other chasers who captured a funnel cloud above the feature. The Mapleton tornado was rated EF3 with several injuries and the southwest corner of town being hit the hardest. Many chasers stopped to help after coming into the town from the southwest and encountering the hardest hit parts.

Lessons Learned: 

  • Don't assume a town has been spared after seeing one part of it.
  • Don't assume a storm is done producing tornadoes while the structure and environmental conditions remain favorable.