Even though it was nowhere near as active as forecast, day 6 was by far our most active day yet. We saw it all: a tornado, tons of wall clouds, an amazing shelf cloud, multiple funnel clouds, and we were pummeled by high winds, torrential rain, and hail on two separate occasions.
The SPC homepage Wednesday night and Thursday morning painted an apocalyptic scenario for the day. In a pink highlighted message at the top, they warned that “some strong, long-lived tornadoes are expected, along with hail to near 4 inches in diameter.” In their “Convective Outlook,” they also designated Central/Southern Kansas and Western Oklahoma as a “high risk” area for severe weather, the highest on their scale.
Credit: Storm Prediction Center
Their map of tornado probabilities (which highlight the probability of a tornado occurring within 25 miles of any given point) was very threatening, with a bullseye of 30% probabilities and hashing, with indicates a 10% potential of a EF-2 to EF-5 tornado striking in a certain region.
Forecasts are one thing, but our simultaneous emotions of fear and giddiness were confirmed when we saw the sounding (from a weather balloon) at Norman, OK (half an hour north of Oklahoma City) at 7 am. In the sounding below, southerly winds are bringing very warm, humid air into the area from the surface, and hot, dry air at mid-levels originating from the Desert Southwest is creating a strong capping inversion with lots of CIN (convective inhibition) to prevent convection from mixing the atmosphere too early in the day. Additionally, we had very cool temperatures aloft, giving us lots of CAPE. And finally, the wind had good directional and speed shear, with the wind veering from southerly to westerly and increasing with height. This type of sounding is called a “goal post” sounding because of its similar look to the goalposts in football, and it’s THE sounding you are looking for if you want severe weather. And to think Norman was only in the “enhanced” zone! If you are curious about how to read soundings, check out this tutorial I wrote on Wednesday, which was an “off day” for us.
Credit: Storm Prediction Center Sounding Analysis Tool
However, Thursday actually ended up having fewer tornadoes and smaller hail than Tuesday. This was likely because there was too much dynamic forcing over the area, allowing storms to pop up earlier and all-at-once. This gave us a broad area of heavy precipitation and stormy weather rather than discrete supercells that are less expansive but pack more of a punch. Still, with a couple days of experience and a little luck, we managed to have our most successful day of chasing yet.
When we left our Econolodge in Clinton, OK at 11:25 am, we had a thick layer of stratocumulus clouds above us, indicating a strong inversion like the one shown in the sounding above. As we drove northward toward Woodward, OK, these stratocumulus clouds began to burn off, indicating that the sun was warming the lower atmosphere and eroding away the inversion (or as its commonly referred to, the “cap”). By 12:40, we were in Woodward, and skies were rapidly clearing. In Woodward, we saw one of the famous “DOW” (Doppler-On-Wheels) vehicles that haul a portable doppler radar around to get extremely high-resolution radar imagery of supercell thunderstorms. These are commonly used to study tornadogenesis from supercells.
In Woodward, we decided to stock up on the three Gs: gas, grub, and a grocery or two. After that, we eyed some storms to our south and headed south to catch them. We stopped at a junkyard along the road to snap a picture of a storm we were chasing, but after seeing how fast it was moving to the NNE, we decided to retrace our steps and head back to Woodward.
Additional storms soon popped up and headed straight towards Woodward. These storms had severe thunderstorm warnings for 60+ mph gusts and quarter-sized hail, so we just decided to wait the storm out at a gas station. These storms also dropped a tremendous amount of rain – a theme that would continue for the majority of the day.
I took a brief video of the chaos before the hail hit and I had to seek refuge inside our trusty Dodge Journey. This video was taken around 3:30 pm CDT.
The Tornado
After the storm abated, we decided to head SE to Seiling, OK to chase a tornadic supercell there. We were more optimistic about this storm because it seemed more isolated from the other storms and therefore didn’t have to share its fuel with any other storms. This storm was also quickly heading north and was well north of us by the time we got to Seiling… it was a rookie mistake on our part to head SE instead of due E. Thankfully, we were able to catch up to it by Waynoka and get some great pictures of a wall cloud/funnel cloud before it died out, and we even got some video of a tornado that was born from another wall cloud with this storm to our north and east!
Even after this funnel cloud disappated, Doppler radar indicated that the storm still had strong rotation, so we headed further north and a little east to see if a wall cloud and tornado would reform. We weren’t alone!
A tornado did indeed reform, and it was a pretty big one too. This the first tornado both Joey and I have seen in the flesh!
The tornado weakened once again as we approached it, and interestingly enough, we began to see research vehicles and professional-looking storm chasers heading the other direction. They must have picked up on the fact that this storm was weakening earlier that we did, but we soon followed suit after the next few radar frames showed rotation weakening as the storm got absorbed into a larger complex of storms further north. At around 6:10, we ditched it for a cell further to our south.
The Shelf Cloud
When you are a storm chaser (especially one without a bulletproof vehicle), you want to fill in behind storms so that you can chase the tornado without having to punch through the torrential rain and monster hail in the storm’s downdraft. Because the storms were so numerous today, this was a tad harder to do. On our way to our original storm, we came across a powerful storm heading directly at us a few miles south of Alva, OK. And unlike the other storms we had seen, this one had a breathtaking shelf cloud.
Shelf clouds are ominous, wedge-shaped clouds that form on the leading edge of a thunderstorm. They form because cold air from the downdraft of a storm spreads horizontally when it hits the surface. This outflow of air originating from within the downdraft undercuts and lifts the warm, moist air rising into the storm upwards, forming a shelf cloud. Indeed, things got downright chilly as this shelf cloud approached… I was shivering!
Shelf clouds form ahead of the “gust front” of a storm; the boundary between the warm, moist air from within the boundary layer (the layer of the atmosphere close to the surface that is heavily affected by diurnal heating and the effects of terrain) and the denser, evaporatively-cooled downdraft from the storm itself. This can be thought of as the “leading edge” of the storm and an advancing gust front is a great example of a “gravity current”, which is where a mass of high-density fluid flowing along a horizontal bottom displaces a fluid of lower density.
We alternated between taking pictures of this gust front and moving back away from it. There was a hefty amount of rotation associated with it… check out these amazing timelapses that Joey took.
Here’s a gallery of images of the shelf cloud. These are arranged in the order they were taken.
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A tornado warning was soon issued, but we decided not to go after this storm because the tornado was “rain-wrapped.” Rain-wrapped tornadoes are particularly dangerous because they are very hard to see. And although I’m a glutton for meteorological mayhem and thoroughly enjoy getting knocked flat on my face by super high winds and heavy rain, getting hit by a rain-wrapped tornado is not my cup of tea. We stayed well south of the brunt of this storm, but we still got pummeled by high winds, heavy rain, and small hail from the downdraft behind the shelf cloud.
After this tornado, things began to quiet down, but we made a quick trip north to Alva to view the sun set on a weaker and drier thunderstorm.
Back at our Clinton Econolodge, there were a ton of chasers, including Josh Wurman of NCAR. He’s done a lot of severe weather research with the “Doppler on Wheels” that I mentioned above, and he was featured in the Discovery Channel’s “Storm Chasers” for a couple years. Most people were frustrated that Thursday didn’t end up being a bigger day, but Joey and I had the adventure of a lifetime. Here’s the full montage of our day.
Today is our last day of chasing – we are headed south and slightly east to Wichita Falls in Northern Texas. We’ll see what today brings!