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How surprise summer thunderstorms happen in Denver

There's a phenomena called the "Denver Cyclone" -- and it explains some things.

A couple of local weather features known as the Denver Convergence-Vorticity Zone and the Denver Cyclone are something that scientists are constantly studying -- and we are still learning about -- but they may help explain surprise summer thunderstorms in Denver.

One of them happened on Saturday evening.

This takes a lot of variables coming together -- at just the right time -- to beat the odds, but here is one possible explanation.

There is a local terrain feature called the Denver Convergence-Vorticity Zone (or DCVZ) that is often responsible for creating something out of nothing.

It happens when we have humid southeast winds coming across the surface of the Colorado plains, but the air is too stable to lift on its own.

This moist air will often converge with dry winds coming off the mountains, usually from the northwest. This zone is the DCVZ, and is a hot spot for convection on a summer day.

The mountain winds were not prominent of Saturday though, so the DCVZ by itself may not have been enough.

In the middle of this zone is the Palmer Divide, an elevated area between Denver and Colorado Springs, which can provide additional lift to create thunderstorms as that moist air rides up the slope.

Combine Palmer Divide upslope with a weak DCVZ and some intense surface heating, and that was probably enough to get the first storms going. Despite these ingredients, there was still not quite enough lift to create thunderstorms.

Enter the Denver Cyclone.

That southeast flow can also create an eddy, as it comes around the Palmer Divide, that gets focused right around the Denver metro area.This is another local feature we call the Denver Cyclone. This creates an even smaller and more local area of convergence.

No way to tell how many of these variables were needed, but they were all possible Saturday.

Then of course, outflow winds from those first few storms collided with outflow coming from storms in the mountains, and the metro got a few additional storms.

This scenario is somewhat predictable when the air mass is a little moister, and more unstable, but with Saturdays air mass, this scenario was extremely difficult to forecast.

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