Friday, August 27, 2010

20 Years Since the Plainfield Tornado

Tomorrow commemorates the 20th anniversary of the Plainfield, Illinois, tornado. It is the only F-5 intensity tornado ever to occur in the month of August and it struck without warning. Because of the lack of warning, 29 people died and 353 were injured even though it occurred in mid-afternoon.

Why was there no warning? There were a number of factors but the most important was the geographic separation between the radar in Marsailles, IL and the warning meteorologists in Rosemont. The image above is from the Marsailles radar while the giant tornado was on the ground. The (likely) hook echo is not seen in this image because it is in the ground clutter (I have outlined the likely shape of the tornadic thunderstorm in pink below).
The radar "technician" in Marsailles did not know to tilt the antenna up to a higher angle to eliminate the clutter and make the potential tornado visible. Because the meteorologists in Chicago could not see the hook and because there were no spotter reports of a tornado, they didn't issue a warning. A later investigation indicated that some law enforcement agencies knew about the tornado but didn't report it to the NWS because they assumed the NWS already knew.

After this and other fiascos (Big Thompson Canyon, Delta 191) with a large loss of life due in part to the separation of the radar and warning responsibility, the National Weather Service underwent a reorganization in the mid-1990's the eliminated this problem. I tell this story in detail in Warnings: The True Story of How Science Tamed the Weather

The Chicago Tribune has this article about the tornado and its damage and a second article about why, if the same tornado were to occur today, there would certainly be a warning. The latter article mentions Warnings.

The image below, from the NWS in Chicago, shows the telltale brown grass caused by the high winds and scouring in a major tornado.

Paul Sirvatka, out storm chasing that day, captured the initial development of the tornado.
The entire video can be viewed here. For those from outside "tornado alley" who have never seen the "green sky" associated with extreme hailstorms and tornadoes, I highly recommend viewing Paul's video as it captures the green sky well.  

We can be thankful that weather science and technology have advanced to the point where a similar event -- entirely unwarned -- is highly unlikely in the future.  

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