Ingredients of a Storm


The events of April 9, 2015 will remain fresh in all of our minds for the rest of our lives.

Chief Meteorologist Candice King warned of severe weather days in advance and was on the air during the entire tornado event.  What happened on April 9th was a rare event for northern Illinois, but it serves as an important reminder that no matter where you live, damaging and destructive tornadoes can and do occur.

Thunderstorms quickly developed that afternoon with many turning severe.  But, it was the storm that developed outside of Franklin Grove and Ashton that would quickly grow into an EF-4 with winds near 200 mph ripping through farm land and homes, killing two and injuring many more.

“The April 9th tornado event was one that showed its hand in advance to be a potentially severe weather day,” said Matt Friedlein, Forecaster for the National Weather Service.  “It had all the ingredients that meteorologists look for severe weather.”

Those ingredients in the atmosphere are moisture, lift, and instability.

“When a severe thunderstorm rides along a turbulent boundary like, it picks up turbulence, which produce a lot of rotation and aid in the development of the tornado,” said Gilbert Sebenste, Staff Meteorologist at Northern Illinois University.

Along with severe weather ingredients, there are certain patterns within the atmosphere that meteorologists look for to help identify if severe weather will even be possible and that’s what meteorologists at the National Weather Service were looking for.

“We’re looking at that pattern trying to relate it to past events,” said Friedlein.  “For example, before April 9th we saw signals as early as three days in advance that correlated to events in the past that led to tornadoes in northern Illinois.”

One of those past events was a tornado outbreak that occurred back in April 2004.

“Past events that had similar patterns as this included the Utica tornado event of April 20th, 2004,” said Friedlein.

It’s important to understand that not all severe weather events lead to tornadoes.  April 9th, however, was not going to be one of those events and as the atmosphere began to show signs that severe storms were likely, that’s when Sebenste began to get worried.

“We knew there was going to be severe thunderstorms and the threat for tornadoes.  But, the question was where, what time, and how bad was it going to be.  Everything was still very questionable up until mid-afternoon, but then the sun came out for a few hours and that’s when we started to get strong heating and as soon as I saw that, I thought, ‘Oh no.'”

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