Following a storm survey on Friday, National Weather Service officials have identified four tornadoes that touched down in the Northern Illinois area on April 9

Officials also say the massive twister seen above that devastated Fairdale was a powerful EF-4 and was on the ground for at least 28 miles. It was was the strongest tornado so far in the country in 2015, and the strongest tornado in both DeKalb and Ogle Counties since at least 1950.

Jon Durr, Getty Images

The other tornadoes have been identified as an EF-0 just east of Lindenwood, and EF-1 south and southeast of Belvidere (this tornado is the one that hit Summerfield Zoo), and an EF-0 south of Cherry Valley.

The atmosphere was ripe for severe weather due to highly anomalous moisture and instability for early April across the region.  A strong low pressure system advanced into this favorable air mass helping to trigger these potent storms.

Further surveying could be conducted this weekend in Boone and McHenry Counties that may result in additional tornadoes being found and/or some adjustments being made to the current numbers.

Thus far, eight tornadoes have been identified in the entire state of Illinois on April 9th.