Tornado Warnings

May and June are the peak months for severe weather in Iowa. More than 50% of the tornadoes occur in these two months.

So far this month all of the action, when it comes to tornado warnings, has been across the southern part of the state. The map below shows all of the tornado warnings this year.

I am going to take this one step further. The map below shows when the last tornado warnings were issued across Iowa, per county. The dark blue areas show the last tornado warning in 2002. The very small white areas have not had a tornado warning from 2002 until now. The circled area in Winneshiek County has not had a tornado warning since 2002.

Sticking with Winneshiek County, here is a look at all of the tornadoes in the county since accurate records have been kept beginning in 1950 through 2016. Notice where the dark blue area is on the map above is the same location of an F3 tornado. It was July 19, 1994 when the F3 tornado traveled 23 miles and was 150 yards wide. Even though there has not been a warning lately, it doesn’t mean severe weather, a tornado, has not impacted the area.



Posted under Severe Weather

This post was written by Schnack on May 16, 2018

F Scale vs EF Scale

This month we are highlighting some memorable weather events in eastern Iowa. Namely, we are remembering May tornadoes that made a lasting impact in some of our communities. However, what do you know of the way tornadoes are rated?

Half a century ago this month, an F5 tornado tracked through Charles City. It was one of two F5 tornadoes that day in eastern Iowa. The other tracked through the Oelwein and Maynard areas.

A little more recently – actually 10 years ago this month – an EF5 tornado tracked through Parkersburg, New Hartford and the surrounding areas.

The difference between these two rankings – F5 and EF5 – is time.

The EF, or Enhanced Fujita scale, went into operation in 2007. This is the scale currently used by meteorologists. Previously, the F, or Fujita scale, was used to rank tornado damage intensity. Click here to find the parameters used for the F and EF scale.

Regardless of which scale was used, the three tornadoes listed above were among the strongest and most destructive in Iowa history. Even EF0 or EF1 tornadoes can cause extensive damage. In 2017, an EF1 struck McGregor in Clayton County. You can read more on that tornado here. In fact, most of the tornadoes in 2017 were ranked EF0 or EF1. For more information on the 2017 tornado climatology, click here.


Posted under Severe Weather, Weather History

This post was written by Rachael Peart on May 16, 2018