Rochelle Tornado Rating

April 10, 2015: The National Weather Service sent out damage survey teams to determine how many and how strong the tornadoes were that struck the Stateline Thursday evening. Today, they were able to put together a preliminary rating on the Rochelle tornado.  This was the massive wedge-shaped tornado that cause an unbelievable amount of damage outside of Rochelle, in Ashton, and in Fairdale. Turns out, that massive tornado was one of the strongest on the ratings scale.

The Rochelle tornado has been confirmed as an EF-4 tornado, preliminarily. The NWS survey team will conduct an aerial survey before the final confirmation.  This will help determine the tornado’s path, how long the tornado was on the ground, and if there were any additional tornadoes spawned from this massive twister (the NWS found evidence of at least one additional tornado).

The preliminary ranking and possible track of the Rochelle tornado

The preliminary ranking and possible track of the Rochelle tornado

The team estimates that the tornado was up to a half mile wide, with maximum wind speeds estimated between 180 and 200 mph. These winds speeds are able to level homes, which we unfortunately saw plenty of across the affected areas in Ogle, DeKalb, and Boone Counties. The survey so far sees this as a long track tornado, on the ground continuously for over 20 miles!

An EF-4 is considered a very violent tornado, and rated as one of the strongest tornadoes possible. In fact, had the winds been a little faster, this could have been an EF-5.

The EF-scale, which rates tornadoes based off of damage and wind speed

The EF-scale, which rates tornadoes based off of damage and wind speed

So why does the rating for a tornado come out after the tornado has struck? First of all, it is hard to determine a tornado’s size and strength based only off of the radar, or by photos or video evidence.  It is also extremely dangerous to be anywhere near a tornado, so its best to wait until the threat has disappeared. Analyzing the destructive power of the tornado helps determine the wind speeds more accurately, leading to the ranking for the tornado. This is why the National Weather Service conducts these investigations afterward.

The process for rating a tornado with the National Weather Service

The process for rating a tornado with the National Weather Service

The Rochelle tornado was not the only one of the day- there was at least one other tornado near Cherry Valley earlier in the evening, plus the possibility of other tornadoes developing near or with the Rochelle tornado. The National Weather Service will continue investigating this weekend, and will have rankings on the other twisters in the coming days.

-Alex

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Posted under severe weather, tornado, weather

This post was written by Alex Kirchner on April 10, 2015

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