Colorado’s windstorm was rare: Stratospheric Intrusion, Tropopause Folding

It turns out this was no ordinary windstorm on 12/15/2021. Based on the evidence, it appears air from the Stratosphere was pulled all the way down to Denver. In Synoptic-Dynamic Meteorology this is called Tropopause Folding. It also means the jet stream descended almost to the valley floor generating those destructive 100mph+ gusts and dust storm.

Credit for this sharp visual goes to Dr. Mathew Barlow:

I had to look back in my college Synoptic-Dynamic Meteorology textbook and re-read the chapter on fronts and jets. I can’t remember such a textbook example in my Colorado forecasting tenure.

A few key points:

  • We live in the Troposphere (the lowest part of the atmosphere).
  • The Tropopause is the top of the Troposphere, like a blanket on top.
  • The Stratosphere is the next layer vertically up in the atmosphere above the Troposphere.
  • Folding the Tropopause is a big deal.

A good visual from my college textbook:

Vertical layers of the atmosphere.
  • Folding of the Tropopause requires strong vertical wind sheer, normally along a front with powerful jet.
  • This folding opens the door for Stratospheric air to mix down into the Troposphere where we live.

Evidence of folding

Ozone levels are higher in the Stratosphere, so a true intrusion would mix higher ozone levels down to the surface.

And what do we find on 12/15/2021? Code Yellow for Ozone.

Ozone levels this high in December are an anomaly.

It was also forecast by the RAP-Chem model. Look at this intrusion!

RAP-Chem Ozone model forecast.

Also of note, there is some concern that aside from ozone mixing down, that radioactive debris from nuclear weapons can mix down. This is a concern in my textbook and something to ponder.

15 thoughts on “Colorado’s windstorm was rare: Stratospheric Intrusion, Tropopause Folding

  1. Mark Sides

    Very cool Chris, I would have never thought it was such a rare and interesting event. Thx for sharing that!

  2. Kz

    Fascinating! Thanks for the visuals and explanations! I hadn’t looked at the atmospheric levels/labels since my kiddo went through his space phase right after the dinosaur phase. 🙂 I love it!

    1. christomer Post author

      Thanks, Barbara, this specific folding wasn’t related to the tornado outbreak. But, the same storm system that snowed on Denver was the storm system responsible for that tornado outbreak. Chris

  3. Mike Andrews

    That’s one slice through the volume. I’d love to see a 3-D model, or a 4-D model showing the volume as time progresses. Should be able to get the data from nearby WSR-88 radars.

  4. Joey

    What exactly is causing the intrusion to mix with radioactive debris? Is it just all the pollution in the sky presently down here? Thanks! Very interesting and concerning.

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