Thunderstorm Wind — Linn, Iowa

2020-08-10 · near Covington, Linn, Iowa

Event narrative

Widespread straight-line winds that produced extensive damage were reported throughout Linn County, associated with a derecho. These winds lasted around an hour in total at any one location, even though the initial line of storms moved out quickly. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were estimated to be 80 to 100 MPH for much of the county, with areas in central Linn County that had wind speed estimates that were 120 MPH or higher. The highest estimated wind speed were in the Cedar Rapids area where extensive damage to an apartment complex occurred with damage indicating winds about 140 MPH. A radio transmission tower also collapsed with wind speed estimated at 130 MPH. These estimates were determined based off damage reports and photos submitted through social media as well as a damage survey. The peak thunderstorm wind gust measured at the Cedar Rapids airport ASOS before it lost power was 68 MPH. The duration of strong winds caused extensive damaged most if not all trees, crops, and structures in their path. Due to the widespread damage, long duration power outages occurred. One fatality occurred here when a 63 year old man riding a bicycle was struck and killed by a tree that was knocked down due to the winds. There were also numerous injuries reported in the Cedar Rapids area.

Wider weather episode

A powerful line of severe thunderstorms produced a derecho which tracked across eastern Iowa and northwest Illinois on the afternoon of Monday, August 10th, resulting in widespread straight line wind damage. The cost of damage from this storm was extreme, reaching an estimated 7.5 billion dollars along the path of these storms from Iowa through Illinois. Two brief tornadoes have been confirmed within the widespread swath of wind damage, one just north of the Eastern Iowa Airport in Linn County Iowa, and one just south of Freeport, Illinois. These tornadoes have been designated as EF-U, as there was no observable damage directly attributable to the tornadoes from which an EF-scale rating could be assigned. While an average of two derechos a year occur across the area, a derecho of this intensity is a roughly once-in-a-decade occurrence. Another unusual aspect of this derecho was the duration of the strong winds, with gusts over 60 mph for over an hour at some locations.

The most extreme winds, estimated at 110-140 mph, destroyed or damaged numerous outbuildings, barns, grain bins, homes, mobile homes, apartment buildings, trees, and power poles in parts of Benton, Linn, Jones, Cedar, and Clinton Counties. The Cedar Rapids area was particularly hard hit. One fatality occurred in Linn County, as a tree fell on a cyclist. Several homes, apartment complexes, and businesses sustained damage consistent with 130-140 mph winds. Radio transmission towers in Marion and Clinton, Iowa collapsed due to winds estimated around 130 mph. Wind gusts of 80-100 mph were common as the line of storms moved through the Quad Cities area and then through northwest Illinois. A small pocket of winds estimated at 100-110 mph impacted Princeton, IL in Bureau County, where a 150 foot communications tower collapsed and numerous power poles were snapped. In addition to the damage, numerous long-duration power outages occurred across the region. Damage to crops was considerable along the derecho path. Numerous semi trucks were also blown off roadways along the path of the derecho.

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Source: NOAA Storm Events Database, event_id 916103. Narrative written by the NWS forecast office that issued the report.