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Boulder’s Tornado Tales: The Science Behind the Storms

When I was re-born in Boulder in 1975, and for some decades after that, it was “common knowledge” that tornadoes could not form close to the front range. Generally it was thought by many that tornadoes West of I-25 were not possible.

We KNOW that is wrong. Personally we’ve seen funnel clouds several miles South of us, looking over Superior and Broomfield, and FAR West of I-25. We’re in the season now when Colorado Tornadoes are possible. How is such a bizarre weather phenomenon created?

Tornado season refers to the time of year when tornadoes are most likely to form in a given region. In the United States, this varies by location.

How Tornadoes Form:
Tornadoes form from severe thunderstorms, particularly supercells, which are thunderstorms characterized by a rotating updraft called a mesocyclone. The formation process includes several key steps:

1. Instability and Lift**: Tornadoes require warm, moist air at the surface and cooler, drier air aloft to create instability. A lifting mechanism, such as a cold front or a dryline, forces the warm air upwards, initiating thunderstorms.

2. Wind Shear**: Wind shear, which is a change in wind speed and direction with height, creates a horizontal spinning effect in the lower atmosphere. This horizontal spinning can be tilted into the vertical by the updraft of a thunderstorm, forming a mesocyclone.

3. Mesocyclone Formation**: As the mesocyclone strengthens, it tightens and stretches vertically, increasing its rotation speed. This is similar to how a figure skater spins faster when pulling their arms in.

Formation of a “mesocyclone” Proceeds the Formation of a Tornado. Dramatically Depicted Over the Plains

4. Tornado Development**: Under certain conditions, a smaller area of intense rotation within the mesocyclone can develop near the ground. This area of rotation can extend downward from the cloud base to form a funnel cloud. If the funnel cloud reaches the ground, it becomes a tornado.

5. Maintenance and Dissipation**: A tornado’s lifespan can vary from a few minutes to over an hour. Factors such as changes in the storm’s structure, the surrounding environment, and interactions with other weather systems can influence whether a tornado intensifies, weakens, or dissipates.

Tornadoes are most common during specific times of the year when atmospheric conditions are favorable, involving a combination of instability, wind shear, and powerful thunderstorms.

During the summer in Boulder, powerful thunderstorms are pretty common. Their concert and light show can be seen day or night, with thunder occasionally shaking the house! Generally if you can hear thunder you are within the “zone of exposure” to the dangers of a thunderstorm. I’ve been chased of a couple of mountains already, and feeling my hair stand up on the back of my neck is something that I can never experience again and still have a complete life, and perhaps a longer one!

Lenny Lensworth Frieling

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