Science, technology behind tornado in Shiawassee County

Tornado touched down Thursday evening

By Paul Gross - Meteorologist

DETROIT - If this were a court case, we’d have more than enough evidence to say that a tornado touched down in Shiawassee County on Thursday evening.  

The only thing left is for the National Weather Service to conduct its standard damage assessment on Friday to make the final, official determination. That process involves much more than just looking for damage.

It first involves looking at the direction that damage was blown around. For example, I recall one live report I did years ago after a tornado touchdown, where I showed trees blown down in one direction, and then a two-by-four driven into the side of a house from an entirely different direction.  

I was actually able to show physically how the rotating wind blew things in different directions. That is one key piece of evidence that my NWS friends will be looking for.

Another thing they’ll be investigating is the types of structures that were impacted. There is a specific chart of wind speed calculations for damage to various types of buildings that will help them estimate how strong the tornado’s winds were.

Finally, they will determine the damage path width and length. But that’s all after the fact.  

Last night, as Ben Bailey and I were intently monitoring the radar, that technology enabled us to deliver a stronger, more confident message about the dangerous tornado that developed. That technology likely saved lives.

First, I want you to look at this series of radar images showing the storm. This is called reflectivity, and it shows where the precipitation is, and how intense it is:

Even to us, meteorologists trained in interpreting radar, we didn’t see anything obvious here indicating that a tornado was occurring.  

In particular, there was no hook echo -- that classic hook seen in many supercell thunderstorms that produce tornadoes. And by the way, Ben and I DID see hook echoes associated with other storms earlier in the evening -- but none of those produced tornadoes that we are aware of.

This story is far from over. Our Doppler radars have products that show us more than just where it’s raining.  Those raindrops are blown around by wind in the storm.  

The radar knows the frequency at which its beam leaves the radar. When that beam hits those raindrops and is reflected back to the radar, it comes back with a different frequency depending upon if the raindrops are moving toward the radar (higher frequency) or away from the radar (lower frequency).

This is called the Doppler effect, and it's the same reason that you hear a train whistle’s pitch get higher and higher as it comes toward you, and then lower and lower as it moves away from you. The radar simply computes the difference in the frequency from when it left the radar and when it returned, and calculates and displays the wind speed headed toward (green) and away (red) from the radar.  If we see a patch of red next to a patch of green, that’s called a couplet, and indicates rotation.  

Now that you know how this works, take a look at the Storm Relative Velocity images from that radar as this storm moved across Shiawassee County, and keep in mind that the National Weather Service’s radar in White Lake is off the image to the lower right:

So, Ben and I were seeing rotation. But not every rotating storm produces a tornado.  In fact, more of them probably don’t than do. We knew we had a storm capable of a tornado, but had no way of knowing IF there was one.

That leads us to another amazing radar product, called Correlation Coefficient (“CC”). This concept is pretty simple. When only rain or snow is falling, then the radar beam is reflecting off of uniform targets.

However, in the case of a tornado on the ground doing damage, you have all sorts of stuff flying into the air: leaves, branches, shingles, pieces of siding, two-by-fours, etc.  When this happens, the radar shows us a little ball of lower CC value on the map.  

We call this a Debris Ball.  And sure enough, we saw a debris ball develop, which told us that we had a destructive tornado on the ground -- and without any eyewitness reports as of yet. Here are those CC images -- the CC values were at their worst around 7:00 p.m. near Durand where you see the dark blue ball, so perhaps start there and follow that general area across the image:

This article shows you how we use our technology to help save lives, and why we attend conferences to stay up to date on our education. Both are necessary in situations like Thursday night.

As with all tornado warning situations where we launch continuous coverage on Local 4 and interrupt regular programming, Thursday night was no exception. And a lot of people were not bashful conveying their anger (sometimes with very colorful language) at not being able to watch Wheel of Fortune and Jeopardy.  

Trust me on this:  we hate interrupting your program more than you do.  But our job as meteorologists, and as a television station, first and foremost, is public safety.  We had a destructive tornado on the ground. People’s lives were in danger.  We did what we are supposed to do, and will do it again when the next destructive tornado is headed toward your house.

One thing some people said is that we don’t need to interrupt their program, because they get alerts on their cell phones.  I cannot emphasize enough how dangerous that mind-set is.  Remember the horrific Joplin, Missouri tornado a few years ago?  That’s the last tornado in American to kill over 100 people, and many people did not get a cell phone alert because the cell system was compromised by severe storms that hit before the tornado.  

That’s why we do our NOAA Weather Radio campaign. Since we began this program, between 40,000 and 45,000 radios have been purchased here in southeast Michigan.

The program continues this year -- here are the locations and dates of our live broadcasts from the Meijer store in:

  • Ann Arbor – April 24th
  • Sterling Heights – May 22nd
  • Westland – June 19th 

Anytime on or in between these dates, you can buy a weather radio at a significantly discounted price at ANY Meijer store.  We hope you’ll consider buying one.  

Remember:  you can program them to warn you only for the watches, warnings and advisories you want to know about, and only the county(ies) you are interested in. So it’ll sit there quietly, and only sound that piercing alarm when it needs to alert you to something you want to know about.

Finally, don’t rely upon the outdoor sirens. Those are not designed to warn you inside your house.

They are OUTDOOR sirens to alert people OUTDOORS about an impending tornado or extremely dangerous severe thunderstorm.

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