“It’s all about the updraft”

College of DuPage meteorology professor Dr. Paul Sirvatka presents at the DuPage County Severe Weather Seminar, March 11, 2017
College of DuPage meteorology professor Dr. Paul Sirvatka presents at the DuPage County Severe Weather Seminar, March 11, 2017

The title of this post is one of the main points of a presentation I heard at the DuPage County (Ill.) Severe Weather Seminar March 11. College of DuPage meteorology professor Paul Sirvatka reminded spotters that the key to spotting a tornado in a classic supercell is knowing where the updraft is. As Dr. Sirvatka put it, a tornado is a “big sucky thing” that forms under an updraft.

Unfortunately, updrafts are not always easy to find. Depending on your location, important storm features can be obscured, making spotting difficult. And the closer you get to a storm, the more difficult it becomes to identify the important features.

We learned in basic SKYWARN training that SCUD clouds (ragged, scary-looking but harmless clouds) should not be confused with wall clouds or funnel clouds. But Sirvatka pointed out that SCUD clouds can be helpful, if they appear to be moving up into the main storm. That upward motion can be an indication of an updraft.

Although the basic spotter class advises us to report wall clouds, Sirvatka is not a fan of this storm feature. He pointed out that while wall clouds can help us identify the location of an updraft, they:

  • Might or might not be present in tornadic storms.
  • Can be seen in any storm that has an updraft, even if that storm is non-tornadic (not rotating)
  • Might or might not result in tornadoes.

Sirvatka therefore advises against reporting wall clouds, unless they contain strong, easily observable rotation. “If you’re asking yourself if it’s rotating, don’t report it,” he said.

Slide from Sirvatka's presentation at the 2017 DuPage County Severe Weather Seminar
Slide from Sirvatka’s presentation at the 2017 DuPage County Severe Weather Seminar

A much more important feature is the development of a clear slot – a bright area where clouds are either absent or much thinner – alongside a wall cloud. A clear slot is a much more reliable precursor to a tornado. If you see one, be sure mention it along with your wall cloud report.

Sirvatka also talked about quasi-linear storm systems, which occur more frequently in northeastern Indiana than do classic supercells. He reminded spotters that in these systems, the updraft occurs ahead of the rain, rather than behind it.

The DuPage County Office of Homeland Security and Emergency Management, located in the western suburbs of Chicago, hosts this advanced severe weather seminar every year in March. It’s well worth the 3.5-hour drive from Fort Wayne. If you’d like to know when next year’s event will take place and you have a Facebook account, join the seminar’s Facebook group. If you don’t have a Facebook account, bookmark the seminar’s web page and start checking it around the first of the year.

Note: This article also appears in the April, 2017 issue of Allen County HamNews.

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