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Monsoon Flooding Threats Continue; Storms Possible in the Mid-Atlantic

Monsoon moisture will primarily stretch from the northern Great Basin to the south and central Rockies. Flash flooding, and mud and debris flows, especially on burn scars will be possible. Strong to severe storms that could produce damaging winds and locally heavy rain will be possible in the Mid-Atlantic, Deep South, and Northeast. Fire weather threats persist for portions of the Northwest. Read More >

Overview

A powerful line of severe thunderstorms known as a "Derecho" tracked across eastern Iowa and northwest Illinois on the afternoon of Monday, August 10th resulting in widespread straight line wind damage. A swath of damage from Benton County, through portions of Linn, Jones, Cedar, and Clinton Counties, is consistent with intermittent straight line winds in the 100-130 mph range. Maximum estimated winds were around 140 mph, which caused extensive damage to an apartment complex in southwest Cedar Rapids, IA. The maximum measured unofficial wind gust was 126 mph at Atkins, Iowa in Benton County. Two tornadoes were also confirmed within the widespread swath of wind damage, Both have been designated as EF-U (unknown), as there was no observable damage directly attributable to the tornadoes from which an EF-scale rating could be assigned.

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 60 minutes, compared to 10 to 20 minutes, which is more common for derechos. One storm-related fatality occurred in the NWS Quad Cities area of responsibility. The Linn County Sheriff's Department reports a bicyclist died after being struck by a falling tree. There were numerous injuries reported, especially in the Cedar Rapids area.

Storms initially developed in northern Nebraska and southeast South Dakota early in the morning, and quickly intensified as they moved eastward into Iowa. Storms quickly became severe in western Iowa, and produced damaging winds near and around the Des Moines metro. At this point, storms began to tap into an extremely unstable environment, and began producing more widespread wind damage as they tracked through eastern Iowa. 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. Several homes, apartment complexes, and businesses sustained damage consistent with 130-140 mph winds. Radio transmission towers in Marion and Clinton, IA collapsed due to winds estimated around 130 mph. Winds 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, and millions of acres of crops were damaged or destroyed. Numerous semi trucks were also blown off of major highways.

NOTE: This information is preliminary. The National Weather Service thanks Emergency Management and media partners, as well as the public, for assistance with remote surveys.

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Radar Animation From the Advanced Weather Interactive Processing System (AWIPS) display inside KDVN. Severe Thunderstorm Warnings are lined in yellow, with Tornado Warnings in red.

Graphic showing preliminary peak winds

Final KMZ file - Updated 10/08/20

Timeline of Watch/Warnings/Reports During Event

     


Video from northern Cedar Rapids near intersection of Blairs Ferry Rd and C Ave. Courtesy: Evan Hindman

 

 

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