Maximum estimated winds were around 140 mph, which caused extensive damage to an apartment complex in southwest Cedar Rapids, IA. Straight line winds of this magnitude are equivalent to an EF3 tornado. The maximum measured unofficial wind gust was 126 mph at Atkins, Iowa in Linn County.
Today (August 20th, 2020), the Quad Cities National Weather Service updated its summary of last week's derecho.
In addition to the quote above, the website says, "A derecho of this intensity is a roughly once-in-a-decade occurrence in this region. Other notable derechos occurred in 1998 and 2011.
"What is unique about this event, making it even more extreme, is the long duration of the high winds. Many locations experienced sustained high winds and damaging gusts for 30 to 45 minuties."
(Previous version)
The Quad Cities National Weather Service continues to analyze the severe windstorm that hit the Midwest last week.
It says the derecho caused widespread damage from Benton County to Linn, Jones, and Cedar counties, and the destruction is consistent with intermittent winds of 110 to 130 mph.
A radio tower north of Marion in Linn County collapsed due to straight line winds estimated around 130 mph. And the weather service says that speed is the equivalent of a strong, EF2 tornado.
Meteorologists estimate the most extreme winds around 120 mph destroyed or damaged many buildings, trees, and power poles in parts of those four counties.
The maximum, measured wind gust was 112 mph at Midway, also in Linn County.
Winds gusts from 80 to 100 mph were common as the line of thunderstorms reached the Mississippi River and Illinois.
In addition, a few storms along Highway 20 produced large hail, with several reports of hail up to the size of golf balls near Freeport.
The Linn County Sheriff's Department reports a bicyclist died after being hit by a falling tree. Numerous injuries were reported, especially in the Cedar Rapids area.
Chicago's National Weather Service reports that 15 tornadoes have been confirmed across northern Illinois and northwest Indiana.
Since 1950, that ties the second highest number of tornadoes to occur on a single calendar day in the counties that are under the Chicago office's warning area.
Fifteen tornadoes is also the most to occur on a single calendar day during the month of August.
In total, Chicago forecasters say the derecho produced 20 confirmed tornadoes in Illinois, Wisconsin, and Indiana.
