August 10, 2020, Midwest Derecho
The costliest severe thunderstorm event in United States history
After storms formed, ten different NOAA National Weather Service Weather Forecast Offices issued Severe Thunderstorm Warnings to communicate the imminent threat of severe weather as storms traversed the Midwest.
Temperatures warmed into the 80s by late morning from eastern Iowa into Indiana, contributing to a significant increase in instability. The area of thunderstorms increased in organization and intensity as it moved into Iowa.
Radar reflectivity at 8AM August 10th and peak wind gusts through that time. Use the slider to swap between images.
Convective outlook issued by the Storm Prediction Center at 8:00 AM on August 10, 2020.
10AM: Morning
During this time period, corn and soybean crops were flattened over such a large area that the corridor of storm damage was visible on satellite imagery. Damage to power lines was also so extensive that power outages were visible from space at night.
Between 2PM and 5PM, storms continued to produce widespread damaging wind gusts as they crossed the Mississippi River into northern Illinois, but the peak wind speeds began to diminish slightly. By the time the line of storms reached Lake Michigan and northern Indiana, the once continuous corridor of extreme winds had evolved into lower-end damaging winds (60 to 70 mph) across a larger area with embedded narrow corridors of more significant wind gusts (70 to 80 mph). The environment also became more favorable for the formation of weak tornadoes.
8PM: Evening
Radar reflectivity at 8PM August 10th and peak wind gusts through that time. Use the slider to swap between images.
In summary, the August 2020 Midwest Derecho produced damaging winds (60+ mph) over an area of at least 90,000 square miles which is home to over 20 million people. The most extreme damaging wind gusts (100+ mph) occurred in portions of central and eastern Iowa as well a few isolated locations in Illinois, and covered an area of at least 2,000 square miles which is home to over 300 thousand people. In some locations, damaging wind gusts (60+ mph) occurred during a 30-45 minute period. Peak estimated wind gusts (around 140 mph) were among the highest known to have occurred in a derecho.
How common are derechos? Where do they occur?
Depiction of a line of thunderstorms with damaging winds. Adapted from a graphic created by NOAA SPC and Dennis Cain.
Derechos can sometimes be difficult to forecast, as the same environmental factors may not always lead to a derecho.
The National Weather Service provides weather, water, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy. These services include Forecasts and Observations, Warnings, Impact-based Decision Support Services, and Education in an effort to build a Weather-Ready Nation. The ultimate goal is to have a society that is prepared for and responds to weather, water and climate events.
The NWS aims to build a Weather-Ready Nation by readying communities for extreme weather, water, and climate events, including derechos.
