COLORADO SPRINGS, Colo. — A strong thunderstorm moved south out of Douglas County on Monday, prompting the issuance of severe thunderstorm and tornado warnings in El Paso County as the evening rush got underway.
The storm developed over the Rampart Range in Douglas County west of Castle Rock and prompted a severe thunderstorm warning in the southeast part of the county as it approached Monument and Black Forest.
In this radar loop, you’ll notice a couple of important things regarding the evolution of the storm that prompted the tornado warnings. First, the storm is moving SSE, while other storms in the loop are moving more SE. This storm takes a right turn from the main steering flow as it moves into El Paso County. Right-moving storms are important because the low-level spin is increased by this movement. This increase in spin became evident on radar and was a key component in the first tornado warning being issued.
The other thing you notice in this loop is a second storm that approaches from the northwest to crash into the original storm. Cell mergers can be an important factor in increasing the strength of the downstream storm. A rotating storm that strengthens can become closer to tornado production due to the increasing vertical wind speeds inside the now stronger updraft.
This loop of lightning strikes over El Paso County also shows the storm collision at about 4:45. Note that between then and about 5:15, the number of lightning strikes jumps up in the new cell. Research is still being done in this area, but there appears to be some correlation between lightning jumps as a leading indicator by about 10 or 15 minutes for tornadogenesis. Not always though, and research teams continue this important work.
The combination of cell merger, lightning jump, and continued radar indication of low-level rotation, and the reported development of a wall cloud with the storm prompted a second tornado warning to be issued.
Here’s a loop of what we call the shear tracks from radar through the late afternoon. Note the darker red areas. These indicate increases in low-level rotation in the storm as measured by radar. One of the areas (over southern Black Forest) occurs immediately after the storms collide and a second flare-up happens as the storm cycles moving toward Highway 94.
What’s great about weather is taking the theory and current understanding of storm morphology and evolution, measurements in real-time on radar, and seeing pictures and video of storm features that match what we think might be happening.
In this composite that I put together for my weather segments Tuesday morning, the first wall cloud photo coincides with the first shear track max, as the storms collide. The storm was really rotating hard at this point as you can see from the video a viewer shot underneath it. The second set of pics and video is what the storm was doing during the second shear track maximum.
As I describe in the video, while this is in the right place for a tornado to form, this specific feature did not appear to be rotating and was more likely caused by warm air lifting into the storm and condensing, versus being the storm circulation descending to the ground to form a tornado.
In short, did we get a tornado? I don’t think so. It was more of a tornaNO!
As you can see from the evidence I presented above, though, the storm really tried. My hunch is that that updraft just wasn’t strong enough to stretch the rotation down to the surface. You see, the stronger the updraft, the easier it is to stretch the storm’s rotation. Really, it’s the conservation of angular momentum. It’s like a figure skater pulling his or her arms in during a spin at the end of the routine. As the updraft stretches vertically, the spin must be maintained over a smaller area. It’s like the figure skater spinning faster because they’ve decreased the area of the spin, except in reverse.
No reports of damage have come in to this point, and there are no clear cut pictures or video evidence that the storm rotation contacted the surface at any point. If you have something that shows it, please send it to me at firstname.lastname@example.org.
As you see at the end of the video, the storm did drop quite a bit of 1″ to 1.25″ hail over northern El Paso County out toward the Falcon area. We can track the hail swaths on radar too.