An ordinary day...

Monday, February 24, 2025 started off like any ordinary weekday for me, wake up at 4:00 am and head into work at my full time manufacturing job. I was aware of the chance of thunderstorms later in the day. In fact, the 12z HRRR model indicated a rotating thunderstorm was possible in eastern South Dakota. This caught my attention, but a part of me figured it was not accurate. This turned out to be a lot more accurate than I initially anticipated later that afternoon. By 3:00 pm, I was getting ready to clock out for the day and head out to watch a thunderstorm that was rolling into town. Nothing could have prepared me for what I was about to witness.

History in the making...

While the Storm Prediction Center was forecasting thunderstorms, weather models painted a broader picture of the environment storms would fire in. While most models showed very little thunderstorm development, most were in support of a vorticity-rich environment that afternoon as an upper level trough dug southeast across South Dakota. However, there were uncertainties in place. With temperatures in the 40s and moisture lacking, would a storm would be able to mature and sustain itself? And if a storm dd fire, would there be enough low level support for any tornado potential?

Using the HREF (High Resolution Ensemble Forecast) Model, a NOAA-run weather ensemble model that uses a collection of mesoscale weather prediction models that are used to forecast convective weather conditions like thunderstorms, it hinted at troughing across the region. While comparing winds and wind direction in each level of the atmosphere (using 500mb, 700mb, and 850mb as examples below), it was evident winds changed direction with height, aka wind shear. This was a key indicator to watch for if any thunderstorms developed as wind shear plays a vital role in thunderstorm development and tornadogenesis. But would this scenario actually come to fruition?

Chase mode activated...

2:30 pm. Radar showed storms firing southeast of Aberdeen, South Dakota moving southeast eventually leading to Watertown, South Dakota. This was my sign to monitor how storms would mature as they continued southeast toward my location.

3:10 pm. I clocked out of work for the day and went to check out the first thunderstorm of the year rolling into town. I was already excited to see lightning for the first time in 2025, but when I first got visual of the storm, that excitement quickly turned to an exhilarating rush of adrenaline at the sight of a well organized base and wall cloud. I had a supercell on my hands.

3:20 pm. I pulled off onto a gravel road just one mile from the building I work in and started filming as constant CG (cloud-to-ground) lightning strikes lit up the sky around me. The wall cloud associated with this supercell was rotating very weakly about two miles west of Watertown. After some filming, I decided to take some backroads and get closer to the mesocyclone as it continued to slowly spin over rural farmland west of town. For a brief moment, an RFD cut was also evident as it attempted to consolidate.

3:40 pm. While this was very short-lived, I continued to follow the storm, realizing at this point, it was in a very favorable environment with incredible amounts of vorticity and steep low level lapse rates. It was just a matter of time if the storm would be able to cycle again and take advantage of the environment it was in.

Tornadogenesis...

3:50 pm. At this point, the storm looked like it was dying off and losing steam. Though, plenty of rising motion and subtle rotation was still evident with this storm. Because of this, I continued to track it around Pelican Lake, back into Watertown, before pulling off a gravel road less than a mile south of town. There, I would sit and watch as rapidly rising scud and weak rotation continued off to my south.

4:05 pm. An organized base developed again as the supercell continued moving off about 5 miles southeast of Watertown while I remained on the gravel road. Scud developed as rapidly rising motion continued and rotation began to strengthen.

4:11 pm. I began to see a consolidated area of rotation before a funnel developed and a dust cloud directly underneath the funnel became more evident. The tornado was born. I began filming as the tornado weakly spun over rural farmland about 10 miles southeast of Watertown or 5 miles east-northeast of Castlewood, South Dakota. Not realizing until 15 minutes later that I was documenting history. This was the first documented February tornado in South Dakota history.

4:13 pm. The tornado dissipated a couple minutes later about 5 miles east of Castlewood, very close to Interstate 29. I still could not believe what I had just documented. The excitement was overwhelming!

4:15 pm. I called in a report of the tornado to the National Weather Service in Aberdeen, South Dakota where they issued an alert on the storm that produced the tornado and filed a report in with No other tornadoes were confirmed.

The environment...

So how did this happen? As I talked a little bit about earlier in the blog, the primary reason behind this tornado had something to do with vorticity! However, that was not the only factor. According to mesoanalysis data, the environment was very favorable for rotating thunderstorms across eastern South Dakota. Plenty of vorticity, very steep low-level lapse rates, high shear values, and troughing contributed to tornadogenesis as the supercell organized and strengthened southeast of Watertown. How do these play a role in thunderstorm development and tornado development?

Vorticity is spin in the environment. It plays a crucial role for rotating updrafts as it creates vertical lifting and twisting motions in the atmosphere and with enough vorticity, a thunderstorm is able to tilt vertically where a rotating updraft is then formed. This supercell was able to stretch vertically and form a tornado. Not all rotating updrafts (or supercells) produce tornadoes, but 70% of all tornadoes come from supercell thunderstorms (just like this tornado).

Low Level Lapse Rates measure the rate at which temperature decreases with height. Rapidly decreasing temperatures create instability in the atmosphere which thunderstorms need to develop. While storms on this day were not very strong, enough instability was in place thanks to steep low level lapse rates in the region. Combine instability with the incredible amounts of vorticity in place, and you get a rotating thunderstorm.

Another factor that played a role in creating this vorticity-rich environment was a developing surface low and troughing. Isobars indicated troughing was in place (note the isobars (black lines) dipping southeasterly across eastern South Dakota) as a weak surface low (red arrows) developed across northern South Dakota and moved southeast. The supercell responsible for the tornado formed on the peak of the surface low (also the left exit region of a upper level trough) ingested the vorticity, where the updraft tilted, stretched vertically, and a tornado was born.

These were not the only factors that played a key role in the formation of this tornado. High shear values, low LCLs, and SRH also contributed. You can find more of this on the NWS Aberdeen review page linked here: https://www.weather.gov/abr/FirstFebTornado.

Another amazing perspective was the wild temperature swings. Just six (6) days prior, Watertown hit a low temperature of -24 degrees F with wind chill values into the -40 degree F range! 5 days later, the high temperature in Watertown hit 56 degrees F with the historic tornado following the next day. A remarkable swing in weather!

Conclusion...

South Dakota is no stranger to weather extremes. With blizzards in the winter and tornadoes in the summer, the weather is never too boring here in the Northern Plains. However, never could I have imagined ever seeing a tornado this early into the year this far north. According to weather data, while this was the first documented February tornado in South Dakota history, it was also one of the earliest tornadoes to occur this far north in North America! This was the earliest tornado I have seen in my storm chasing career, beating last year where I saw tornadoes on February 27, 2024 in northeastern Illinois. It was also the 70th tornado of my career, dating back to 2020. Be sure to check out the full chase highlight video at the top of this blog if you haven't already!

Until next time...