On August 10, 2020, a large and intense line of thunderstorms known as a “derecho” swept across much of the Midwest producing wind damage to an area more than 90,000 square miles. The derecho resulted in $11.5B worth of damage, making it the COSTLIEST known thunderstorm event in modern U.S. history. Peak wind gusts topped 140 mph in Cedar Rapids, Iowa, and at least 26 tornadoes were spawned by the storm. More than 20,000,000 people lived in the damage footprint of the derecho, with at least 1,000,000 customers losing power — some for more than 2 weeks. Numerous injuries were counted after the storm, and four people lost their lives.
In the NWS Chicago County Warning Area (CWA), over 160 reports of damaging winds were received and 15 tornadoes were confirmed, including an EF-1 tornado in the Rogers Park neighborhood of Chicago. The derecho stands as one of the most impactful weather events to ever impact the NWS Chicago County Warning Area. Additionally, as of 2021, August 10, 2020 is tied with June 22, 2016 as the single calendar day with the 2nd most tornadoes within the NWS Chicago County Warning Area behind the 6/30/2014 “Double Derecho” event.
- Preparedness: Despite the massive coverage and impressive intensity of the wind damage, there were a limited number of serious injuries. This speaks to the effort of our partners including fellow meteorologists in the weather enterprise effectively communicating the threats and action needed to be taken, as well as emergency management and law enforcement for their preparedness efforts beforehand and assistance efforts immediately after. Of course it also means that many public citizens heeded the threat and the warnings, as well as communicated them to their family and friends (being a “Force of Nature!”). For more on severe weather preparedness, see here.
- The Forecast: Forecast confidence increased markedly Monday morning that severe weather was likely across northern Illinois and northwest Indiana that afternoon. At NWS Chicago, our messaging accordingly increased, and we issued a Situation Report (briefing) for our partners at 9:15 a.m. and held a conference call with them near 12 p.m. The office also issued eight Severe Thunderstorm Warnings and six Tornado Warnings.
A total of 15 tornadoes were confirmed across northern Illinois and northwest Indiana in the NWS Chicago County Warning Area.
Tornado #1: Southwest Rockford, IL EF-0
A very brief tornado touched down near the intersection of Pierpont Ave and Montague Road and continued northeast into the southwest side of Rockford. The tornado ended near the intersection of Ferguson and Loomis Streets. All damage was to trees along the tornado path.
Tornado #2 – Rockford to Caledonia, IL EF-1
This tornado was associated with the same supercell thunderstorm that produced an initial brief EF-0 tornado immediately southwest of Rockford, but it has been determined these exist as two separate tracks. This tornado developed as the main line of thunderstorms caught up, and eventually merged with, the parent supercell with this path starting near Guilford Road just north of Rockford College before heading northeast. Significant tree damage, consistent with EF-1 wind speeds, occurred in a localized area immediately east of Rock Valley College west of North Perryville Road. The tornado continued northeast, crossing I-90/39, producing sporadic damage before lifting near Caledonia Road.
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