Thunderstorm Wind — Cook, Illinois

2020-08-10 · near Dixmoor, Cook, Illinois

Event narrative

A corridor of significant straight line wind damage occurred from Harvey east to Calumet City. Numerous trees were uprooted and snapped along this corridor. Some roofs were damaged by falling trees; other roofs suffered minor shingle damage from the strong winds. Some of the worst damage was in Harvey in an area between Sibley Boulevard to the north and 159th Street to the south. Trees were snapped and uprooted and extensive damage occurred to utility poles and power lines, resulting in some portions of the power grid needing to be completely rebuilt. Almost everyone in Harvey lost power. An estimated 300 to 350 trees were blown down in Harvey. Almost every road in Harvey was blocked by some amount of tree damage. Significant tree damage was reported in forest preserve areas including in the Shabonna Woods Forest Preserve. Damage was consistent with wind speeds up to 90 mph.

One day later, on August 11th, just after noon, a 59 year old man was walking in the 15000 block of Merrill Avenue in unincorporated Thornton Township near Calumet City. He stepped on a downed power line that was live and collapsed in a grassy area where he died.

Wider weather episode

During the late morning through the afternoon of Monday August 10th, a line of intense thunderstorms known as a derecho brought widespread severe wind damage across Iowa, northern Illinois and northern Indiana.

In north central and northeast Illinois alone, the severe winds of 60 to 100 mph downed or damaged tens of thousands of trees, as well as caused severe damage to homes, businesses, and infrastructure. There were 10 injuries reported in north central and northeast Illinois within the NWS Chicago/Romeoville County Warning Area (CWA). Local officials estimated that nearly one million customers lost power across northern Illinois at the height of the derecho and some people were without power for several days. Damage was estimated to be in the hundreds of millions of dollars in north central and northeast Illinois, with several billions of dollars in damages across the entire Corn Belt region including significant damage to crops and agriculture infrastructure. While much of the damage was due to straight line winds, there were also 14 tornadoes documented in north central and northeast Illinois.

The combination of high moisture, explosive instability and very strong atmospheric wind flow for mid-summer had developed quickly over the Corn Belt region on the morning of August 10th. This resulted in a progressive, well-organized complex of storms for hundreds of miles and at times traveling nearly 70 mph. After bringing extensive damage from extreme wind speeds in Iowa that morning, the damage transitioned across northern Illinois from widespread wind damage to narrow, brief and intense swaths associated with compact circulations within the thunderstorm line, some of which were associated with tornadoes.

View location on OpenStreetMap → (41.6172, -87.6818)

Source: NOAA Storm Events Database, event_id 915489. Narrative written by the NWS forecast office that issued the report.