June 11, 2018 Louisville, NE Tornado and Supercell

On Monday, June 11, 2018, I was working at the National Drought Mitigation Center on the first draft of that week's U.S. Drought Monitor. For most of the day, storm chasing was the last thing I was thinking about, as we pored over meteorological, hydrological, and satellite-based drought indices to update the USDM map. I knew in the back of my mind that there was a chance for severe weather in east-central and southeast Nebraska late that afternoon, but given how arduous of a task the USDM is, I did not give much thought to chasing in the morning, thinking that there was no way I'd have time. Providentially, we finished making our first round of edits for the initial map draft far earlier than I anticipated, and once I started realizing we were ahead of schedule, I took a quick glance at the SPC page and started to look at surface observations. A mesoscale discussion indicating the likely issuance of a tornado watch for eastern Nebraska made me more optimistic (since I was at work and working on USDM, I had very little time to look at any current weather data myself outside of areas where we were considering changes to the map).

Finished product on Wednesday for that week's US Drought Monitor. That week's author was Brian Fuchs, who I was working with that day.

When we finished the first USDM draft, I took a quick look at data in my office before leaving. While my memory is a little rough from this day, I recall there being a bit of an outflow boundary left behind by morning storms, draped west-to-east just to the south of the Omaha metro. A cold front was also coming into eastern Nebraska from the northwest, and this would initiate storms west-northwest of Omaha, though it was clear that these would likely become linear early on, and would probably have lower tornado potential. I drove east on US 34 out of Lincoln (with music from Twister playing on my car speakers, because why not?), and spotted organized cumulonimbus to my north. I guessed that the storm I was now targeting may have been rooted along the remnant outflow boundary.

From here on, my memories of this chase are a little fuzzy, but here's my best to accurately recount it:

I was well south of the developing supercell south of Omaha for a while, traveling eastbound on US 34, until I arrived at the eastern end of Nebraska and US 75. From here, I went north, and I think I backtracked a bit west somewhere near Plattsmouth, NE, in order to get a better look at the structure of the very slow-moving supercell. While the low-level mesocyclone was still likely about 10 miles away, I could tell that the low-level rotation was gradually getting better organized. Despite all of the haze that afternoon, I had a decent view of the low-level structure from my vantage point (still roughly 10 miles from the storm). Photos below give you an idea of the structure:

Wall cloud, looking northwest

Wall cloud, perhaps funnel cloud, looking northwest

While looking to the northwest, I noticed a vertically oriented pillar of cloud suddenly form, which had contact with both the ground and cloud-base. I figured at the time that this may have been a tornado; I confirmed this later with reference to an NWS storm survey (compared to when the picture of this was taken, and based on close-up video taken by YouTube user Live Storms Media, linked here). This was the Louisville area EF-0 tornado, shown in the photograph below (it's low contrast, so hard to make out):

Louisville, NE tornado (rated EF0)

 After this tornado dissipated, I followed the storm as it slowly drifted east-southeast and gained more high-precipitation characteristics. While I did not see any other tornadoes, the storm did produce at least one other tornado about 50 minutes later, which I elaborate on in one of the photo captions. The HP structure was mesmerizing to watch slowly drift across the plains/lowlands of eastern Nebraska.

One or more tornadoes were occurring at about 6:30 CST when this picture was taken, and these were rated EF0. While chasing, I suspected that a tornado was taking place, due to the visually evident tightened low-level rotation, low-based cylindrical wall cloud, and rapid increase in the strength of the inflow, but due to the HP structure, I couldn't confirm a touchdown visually. I confirmed that there were tornadoes during this period a couple years later (while writing this entry) by sifting through storm survey data from this day and comparing it to time stamps on my photos. This photo captures the structure during this tornadic phase well.

Tornadic phase of supercell, with cylindrical wall cloud. The tornado(es) during this phase were rated EF0 (see above paragraph for details).

After this tornadic phase, the supercell became more outflow-dominant, and trailing storms along the cold front caught up to it. The resulting squall line surged ahead and produced widespread severe winds. At this point, I was quickly moving south to try to stay ahead of the storm (both me and the storm were headed southeast towards Nebraska City). At one point, a tornado warning was issued while the storm outflow was accelerating (likely due to a spin-up circulation somewhere along the gust front), and I pulled off on a gravel road to avoid where the area of rotation was purportedly going (car radio tornado warning announcements were quite useful for doing this).

Storm becoming outflow-dominant just north of Nebraska City

Once the gust front had passed, I made my way to NE highway 2, and drove back to Lincoln. When I returned home, I was treated to a gorgeous mammatus display under the anvils of the MCS which had developed by the time I got home. All-in-all, this was a fantastic chase day, considering that I saw one or more tornadoes along with beautiful supercell structure, I didn't have to go far from home, and I got a full day's work on the US Drought Monitor in, all on a day when I was not planning to chase when I got up that morning.

Mammatus display from my backyard (looking southeast)!