The Supercell
It’s a beast. Supercell thunderstorms can produce copious hail, torrential rainfall, strong winds, fierce downdrafts, and even tornadoes. While they are the least common type of thunderstorm, they are the most ferocious.
All thunderstorms require lift, forcing air upwards to the point of becoming positively buoyant. Also, instability (atmospheric energy) is required for the air to rise. Finally, moisture (typically mid-60s dew point) is necessary. So, what’s the additional ingredient needed for a supercell?
It’s wind shear. Wind shear is caused by differences in wind speed and direction over a relatively short distance in the atmosphere. Shear can induce a storm’s updraft to begin rotating, forming a mesocyclone, the signature feature of a supercell.
From Mesocyclone Diagram
Mesocyclones begin with horizontal rotation. Winds from two different directions and speeds (the red arrows) at two different altitudes create shear, imparting rotation (the green arrow) to a parcel of air. Then, a strong updraft (the blue arrow) begins to tilt the rotating parcel of air progressively vertically, creating a deep, tilted rotating updraft (the mesocyclone).
From Wikipedia
In an ordinary thunderstorm, rain and cold air falling through the updraft chokes off the updraft, killing the storm.
Tilt pushes the hail and rain ahead of the updraft. The unimpeded mesocyclone can continue to fuel the supercell for hours.
Tornado Alley
Tornado Alley is the hotbed of supercell and tornado activity. This part of the country hosts the perfect convergence of the jet stream, cold dry air and wind from the north, warm dry air and wind from the southwest, and warm moist air and wind from the southeast.
Shear, lift, instability, and moisture are abundant in the Spring and Summer. Tornado Alley is now centered further east due to climate change, and winter storms are more common.
From https://kristanwevvie.pages.dev/pmllvwy-tornado-alley-2024-ymvvzcp/
The Shot
As you know from my last Friday Photo, I’ve been away chasing storms for 11 days. On June 2, my first day, we began chasing storms in the Wyoming/Nebraska area.
At 5:30 pm we set up near Merino, Colorado. Next to me on this storm was experienced storm chaser and timelapse expert Tom Trott from London, England.
His timelapse of this Friday Photo’s supercell approaching our position is at https://youtube.com/clip/UgkxvlWNYSfLD3UndHgR9a1yOtd5TKQ0YbAR?si=8P9oW2tBAcGDWzKv It ends just as we needed to “bug out” due to approaching hail, rain, and high winds. Thanks for sharing, Tom!
Of the many pictures I took of this beautifully structured supercell, this one with a lightning bolt is my favorite. While it didn’t produce a tornado, standing in awe of nature’s fury is an equally rewarding experience.
Thanks for looking,
Chuck Derus