May 17th, 2017 Iowa/Illinois Supercells and Brief Tornado
Tornadoes: 1
Largest Hail: 1"
Highest Wind: ~60 mph
It was mid-May, and tornado season across the central US was finally beginning to pick up. Just the day prior, on the 16th, there was a big chase day in the Texas Panhandle where a number of chasers witnessed a career event. And the potential for a tornado outbreak across the southern Plains was looming for the 18th. I, on the other hand, had graduation to tend to, so a Plains trip was not something I was able to do. The 17th, however, showed potential over portions of Iowa as the system that produced the day prior moved northeastward. Shortwave energy was ejecting over the mid-Mississippi Valley as a strong surface low pushed into the Siouxland area. A broad area of backed winds was progged to set up ahead of this low, along with modest moisture and CAPE. The potential was there for a handful of tornadoes over much of Iowa.
500mb winds:
Surface MSLP and winds depicting a robust surface low backing winds out ahead of it:
Accordingly, SPC went with a 10% area, adding hatching to it at 20z:
Matt Zuro was the only person available to partner up with, as Matt Magiera, Scott Matthews, and Isaac Polanski were in the middle of their Plains excursion, and Paul Sieczka and Daniela Barrios were busy. Matt had no way of getting to my place in north-central Illinois from the suburbs, so I had to leave early to pick him up from Aurora. After he was in the vehicle, we started back west, getting onto I-80 where we continued into eastern Iowa.
After a quick stop for gas and something to eat, we meandered through east-central Iowa for some time as storms were struggling to go up. We eventually started going a bit northward toward Cedar Rapids as we noticed dewpoints dropping further south. SPC also added the hatching for this area, so we felt pretty confident about our decision. Sitting at another gas station outside of Cedar Rapids, we noticed a number of cells organizing 30 miles or so to our south. Exactly where we just abandoned. We stayed put, but eventually the cells formed into a cluster of scattered supercells, some of which were going tornado warned. We floored it back south to try and catch up with these storms.
Here lied the biggest issue with the setup that day: the best storms were going up in marginal moisture. Surface obs at DVN at 21z were 83/59, pretty disastrous if you want any shot at a tornado. The MD for the newly-issued tornado watch highlighted exactly what we were noticing (and feared):
It didn't stop us from trying. We core punched the most promising looking storm at the time, encountering some quarter-sized hail. Emerging from the rain, the base looked...unimpressive. It was virtually featureless and was ridiculously high up. We drove directly under it with no fear, even though it was tornado warned. We came into the town of Wapello where we stopped in the park for the only clear view (this part of Iowa is full of trees). After watching for a bit, we noticed an RFD cut working into the updraft, along with what we were pretty sure was a nub funnel. I contrast enhanced the frame grab I pulled:
It didn't touch down from what we could see, and the sky-high base heights helped assure that. We started north again, though, just in case it did tornado, and in order to keep up with the storm. The funnel dissipated as it occluded, but it cycled as we came closer to Muscatine. In a construction zone south of town, we observed a well-formed blocky wall cloud to the east, with no rain to obscure our view.
We saw no apparent funnel or even substantial motion in the wall cloud at the time, but another chaser on the Illinois side of the river was able to confirm a brief ground circulation. There were a few persistent nubs hanging from the lowering, though, and I suspect those were probably associated with it. Time stamps on my video line up with the timing listed by the NWS.
DVN damage survey:
Video:
We continued following the storm northward, but it eventually ended up falling apart. We found ourselves in Davenport, and it was still mid-evening with storms ongoing, so we didn't want to give up and miss any potential show still left. We decided to stay on the Illinois side of the Mississippi River since crossings were very few, and storms would soon cross into Illinois anyway. We'd also heard numerous reports of significant traffic impacts along I-80 in Illinois from a dust storm created by synoptic winds blowing dry, freshly plowed farm fields, so we thought it'd be a good idea to avoid that. We meandered southward from the Quad Cities, and found a McDonald's to sit at. We were ordering as everyone's phones started blaring. A tornado warning was issued for a newly-formed cell to our southwest. We endured the brutal wait for our food, then sprinted to the car to drive south for an intercept. Racing toward the storm, we really began to encounter the dust storm we were hearing about. Visibility wasn't significantly reduced, but it created eerie lighting conditions, especially given the presence of robust convection. We finally came to the town of Little York, IL, where sirens were blaring. We found a good spot to stop south of town as a relatively high-based wall cloud with some modest motion sucked in scud. There were also a number of CG lightning strikes nearby.
The circulation began to occlude, but another was forming right next to us, and moving directly in toward us. We took an escape route northward back through Little York before finding a location just east of its path northeast of town. I braked pretty suddenly when we pulled over, and part of my roof rack careened off the vehicle and onto the road. RFD was starting to come in, so I had to run out to grab the plastic piece we lost. The joys of owning a 15 year old vehicle.
The RFD started carving into the meso, rain curtains visibly racing west to east from our location. A little nub tried reaching down from the center of rotation, another futile attempt at tornadogenesis this day:
The storm then fell apart as another disorganized cell merged with it. We started home down some back roads when we ran into Cory Marshall. We stopped to talk with him for a few minutes as a tornado report came in 5 miles to our north, causing us all to start scrambling back into chase mode as we said our goodbyes. The tornado was rain-wrapped, and it was dusk, so trying to see anything was hopeless. Matt and I once again started heading back home.
After I dropped Matt back off in Aurora that night, a number of storms were firing ahead of a line that was moving in from earlier in the day in Iowa. It was after midnight, and I noticed some impressive CGs flying off the isolated storms in clear air to my east. I stopped somewhere near Norway, IL to try and capture a few bolts. And I was not disappointed:
The day's chase fell short of our hopes (it was Iowa, what did we expect?), but it wasn't the worst it could've been. Had moisture not been lacking, I think we could've been dealing with a localized tornado outbreak across eastern Iowa into northwest Illinois. DVN's 00z sounding observed LCL heights of *1400 meters*, and you won't see any substantial tornadoes out of that unless you're in Colorado on the one random 2% sleeper day.
Overall, a couple decent storm intercepts were much-appreciated given what we were missing out in Tornado Alley, plus we at least got to say we caught a tornado, as wimpy as it was.
SPC Storm Reports:
Still itching.
