August 14, 2020 NE/KS Southwest-moving Supercell Cluster

It is often said that, in order to appreciate experiences on storm chases, one should check their expectations beforehand. On the vast majority of storm chases, you are not going to see a tornado. I've been on plenty of chases when surface-based storms failed to develop, much less produce beautiful structure and/or tornadoes. So when chases vastly exceed expectations, as happened on this day, senses of awe and excitement can spontaneously overflow. 

The morning started with few thoughts of chasing storms; rather, I was having dental work done at 7 a.m. I knew SPC had us in a slight risk for severe weather in the afternoon, as a cold front was forecast to move into eastern Nebraska from the northwest. There was ample instability forecast to be present (see very steep mid-level lapse rates observed on OAX 0Z sounding), and a shortwave trough approaching in northwest flow aloft (see 500 mb map), but the deep-layer shear was forecast to be marginal (~30-35 kt in eastern Nebraska) for supercells, with better chances for rotating storms, and possibly tornadoes, in Minnesota. While worked from home in the afternoon, my friend Matt was also fairly skeptical of supercells occurring within a few hour drive of Lincoln, telling me that radar trends with early convection initiation in northeast Nebraska looked fairly blobular, which I agreed with. 

0 UTC Omaha, NE Sounding, Courtesy NWS Omaha and NWS SPC

 

0 UTC 500 mb map, courtesy NWS SPC

About an hour later, Matt noted a few broad mesocyclones in cells near Norfolk and Madison. Based on this, and the hope that one of these storms would become dominant and turn more to the right, we drove north on US 77 to Wahoo to get into initial position, arriving after 3. As we approached Wahoo, the storms in northeast Nebraska weakened, while a storm in the Columbus vicinity maintained a broad mid-level mesocyclone, as new cells developed to its southwest along the cold front and merged into it. Whatever was to become of this became the obvious target, so we headed west through the rolling hills of the Bohemian Alps region, gaining a visual of a very broad updraft base when we neared David City. Occasional updraft towers just beyond the southwest flank of the storm continued to develop. While the broad updraft base was encouraging, the lack of a consolidating, dominant updraft and a messy appearance on radar imagery led us to believe that we'd likely get to watch a multicell cluster of storms move south, to the west of Lincoln. We stopped to watch the storm near Garrison, where it very slowly became better organized, showing off picturesque mid-level inflow bands before we had to move south.

Storm west-northwest of Garrison, with mid-level banding, after we found somewhere to watch it without corn obstructing our view. Eventually, to avoid rain and hail, and increasing cloud-to-ground lightning, we moved south.

We followed the storm south-southwest after leaving Garrison, passing through the communities of Ulysses and Staplehurst, eventually crossing I-80 south of Utica, where the structure had changed to a narrower, tilted updraft. Still pretty, but nothing overly impressive yet. Several miles south of I-80, Matt looked out the right and exclaimed "Whoa! Funnel cloud!". A funnel cloud, condensed more than halfway from the cloud base to the ground, came into view as we topped a ridge. As we suspected, this had a ground circulation, and was rated an EF-0 (near Henderson, NE). Matt's picture (while I was driving) of tornado #1: https://twitter.com/mattwilsonwx/status/1294397505489244167.

This first tornado lifted, but it became clear to us that the storm was taking advantage of increased environmental vorticity along the cold front, and given the updraft's proximity to the front, more tornadoes seemed possible (see mesoscale discussion from that afternoon by NWS SPC's Evan Bentley for a more detailed analysis of the mesoscale environment which lead to repeated tornadogenesis). About 20 minutes later, we pulled off of US 6 near either Exeter or Sutton, and watched tornado #2 (also rated EF-0). 

Tornado #2

Tornado #2 with storm structure

Tornado #2

In a state of bewilderment that Matt and I had seen our first tornadoes of the year in August, we continued to US 81 to follow the storm southwest. We pulled off of US 81 northwest of Bruning, NE, where a wall cloud and other impressive, albeit low contrast, structure came into view. 

Mesocyclone, wall cloud, and mid-level banding (barely visible on right side of photo) along forward flank near Bruning, NE. As would become a theme for the rest of the chase, the vibrant textures and colors in the storm features were difficult to capture in their full splendor in photographs.

As the precipitation from the storm encroached on our location, and new updrafts began forming to the southwest, we continued southwest to Superior, NE, where a new updraft to the west was becoming dominant. After a successful escape from hail and heavy rain in the forward flank, we got back ahead of the storm as we crossed south into Kansas. Several miles into Jewell County, KS, the mesocyclone associated with the new western updraft became visually stunning, with deep purple, blue, and green tints, and otherworldly textures and shapes. Sadly, I had difficulty capturing how awe-inspiring the structure was when we pulled off, but hopefully these photos somewhat convey the physical structure. 

Northern Jewell Co, KS, structure. Not apparent in these photos is how well-defined the striations were in the mesocyclone, or how vibrant the colors in the updraft were.

We continued to follow the storm complex southwestward, where it gradually morphed into outflow dominant structure, though this happened slowly, as new updrafts would develop mesocyclones to the southwest of whatever the ongoing one was that was becoming dominated by outflow. The colors in the updraft and outflow bands and striations had an ethereal beauty to them, with rich aquamarine, green, and purple common near the updraft, and a glowing yellow-orange behind the deep purple bands along the forward flank convergence zone. 

Structure on both forward and rear flanks as storm gradually became more outflow-dominant (Jewell Co, KS).

New mesocyclone to southwest of old one.

Waves on edge of mesocyclone, perhaps a result of horizontal shearing instability.

 

Storm becoming more outflow dominant.

 

 

As we arrived in Beloit, we realized that the sun would set sooner than we could get into position to photograph mammatus, so we ended the chase and headed north, with a stop at a Dairy Queen in Belleville, KS along the way. 

Relative to the expectation of seeing a multicell cluster, or a likely weak supercell, the storms which we saw on this day were incredible, with a couple tornadoes and beautiful, constantly changing structure. After the stressful year thus far, and a handful of frustrating chases in June after marginal setups in May, this was a fantastic way to see my first two tornadoes of the year, and my first two August tornadoes.

Chase Route

 

May 3, 2020 Western Nebraska Supercells

On the morning of May 3, 2020 (an infamous day in May in weather circles), I seemingly didn't have much to do. Due to the COVID-19 pandemic, the Lincoln Diocese had cancelled in-person Mass, so instead of church, I ran a couple errands early that morning and took a hike around Pioneers Park while catching up with my family over the phone. In the back of my mind, I remembered that SPC had a marginal risk for severe storms outlines in western Nebraska and surrounding regions in the High Plains (several hundred miles to the west of Lincoln). Knowing that slow storm motions were likely, and that the tornado risk was quite low (due to a lack of moisture in the post-frontal upslope regime that afternoon), I figured that it could be a relatively low stress first chase to take my girlfriend on. Plus, gas prices were quite low due to the side effects of the pandemic. So after a quick bit of discussion, the chase was on (albeit, with quite low expectations), with an initial target somewhere around Ogallala, NE, where we expected high-based, slowly moving marginally severe supercells.

We left Lincoln around 11:15 and headed west on I-80; initially, we had overcast skies near Lincoln, though skies generally became mostly sunny as we passed to the west of Grand Island (as a sign of the times, we were also doing a Zoom call with my cousins over the car speakers). Once we got west of North Platte, we drove under a high-based cumulus field, which gave way to convective initiation in northeast Colorado and near Lisco, NE (between Ogallala and Scottsbluff). While stopping for gas in Ogallala, our first major decision was whether to drop south into northeast Colorado to chase a cluster of storms which had the potential to merge, or to chase the more discrete (but initially weaker) cell near Lisco (moving slowly southeast to the north of US 26), or to move north into the Sandhills, where the most recent runs of the HRRR showed a comparatively stronger supercell moving southeast out of northwest Nebraska (in an environment which seemed to be slightly more supportive of supercells, too).

We went north towards Lake McConaughy (the instability to the north seemed to be better), and at the last second, I decided that the cell off to the west along US 26 looked stronger and better organized than the one moving towards the Sandhills. We drove to the west (along the north end of the Lake McConaughy settlements), and then went west on US 26, eventually catching up to the supercell drifting southeast towards us.

To my disappointment, it was initially difficult to see much in the way of supercell structure (we had gotten too close to the base, and low clouds had shrouded our view from farther east).

We were way too close initially to see anything other than the storm core.

As we had driven all the way from Lincoln, it only made sense to pursue the storm as it drifted southeast towards Ogallala, to see if the structure would become more interesting. Thankfully, it did.

Weak supercell with flanking line, and a transient wall cloud.

We stopped several times to watch the storm as it drifted southeast towards Lake McConaughy. Once the high-based mesocyclone made it to the lake, our vantage of the structure became quite unique (this was the first time I had watched a supercell with a body of water in the foreground).

As this supercell passed over the lake, another supercell was moving southeast through the Sandhills to our north, and appeared on radar to be strengthening, while the southern cell began to weaken and become elevated above a stabilizing boundary layer to the east. However, due to the hail threat with the Lake McConaughy cell (which at that point was still severe-warned), we chose to drop south to I-80 to position east for the Sandhills cell, rather than intercept the Sandhills cell near Arthur.

During a quick break in Sutherland, the southern cell which we had been chasing rapidly weakened and became very elevated.

Rapidly weakening southern cell from near Sutherland, NE

After our break in Sutherland, we drove north into the Sandhills (my girlfriend's first venture into the Sandhills, as well!) to intercept the northern cell before our road turned to gravel (we never made it to the end of the paved section). Once we made it through the remnant forward flank of the southern cell, an elongated, mostly elevated updraft and wall cloud came into view on the northern cell. At that point, we found a spot to pull off the road, listen to the birds sing in the Sandhills, and enjoy the early evening lighting in the Sandhills while watching both cells weaken as they moved off to the east.

Initial view of northern cell.

Rapidly weakening southern cell, as it raced off to the east, leaving behind a rainbow and a view of the moon.

Northern cell weakening.

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)!