Storms on the radar · August 10, 2020
The Midwest derecho, 2020
Opens HookEcho on KDVN at 2020-08-10 17:00:00 UTC and loads the archived volumes for that day. The archive goes back to 1991.
On 10 August 2020 a derecho crossed 770 miles from South Dakota to Ohio in 14 hours. Gusts reached 140 mph near Cedar Rapids. It flattened roughly a third of Iowa’s corn crop and became the costliest thunderstorm event in US history.
What the radar shows. The link opens on velocity from the Quad Cities radar. A derecho is a wind event, so reflectivity alone undersells it: the bowing line looks like a squall line and not much more. Velocity is where the rear-inflow jet appears, a slab of inbound air punching through the back of the line and reaching the ground as the damaging gust.
Step the loop and watch the bow accelerate. The line is moving faster than most tornadic supercells travel.
Archive volumes come from NOAA's public NEXRAD archive on AWS, the same source the National Weather Service publishes. Nothing here is a re-render of someone else's picture.
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