Derecho 2.0

 

Storms began forming in the state of South Dakota during the morning hours of Tuesday, July 5, 2022, and began picking up steam by late morning. By early afternoon storms began forming a powerful linear state, with hail and wind speeds reaching 100 mph--the early stages of yet another derecho. Severe thunderstorm watches went up for NW Iowa at 1:40 pm CDT and 3:50 pm for central Iowa. As storms advanced eastward, the Storm Prediction Center (SPC) upgraded an Enhanced Risk in SE South Dakota and NW Iowa to a Moderate Risk, valid from 3:00 pm CDT (above). 

4:35 pm. Severe Thunderstorm 440 is posted for eastern Iowa.

Radarscope image 4:46 pm. Storms entering NW Iowa are starting to form the classic derecho signature (left), and at the same time a boundary layer-induced line of storms are popping up in NE Iowa, SW Wisconsin and northern Illinois (right). 

6:09 pm. Active radar signature. Well-formed derecho at left. Note the tornado warning near Crystal Lake, Illinois at far right.

6:11 pm. Impressive reflectivity image of the derecho, packing winds up to 100 mph, just west of Fort Dodge, Iowa.

6:20 pm. Large picture of storms in Iowa and Illinois.

6:59 pm. Looking west over the Collins Aerospace facility from Volley's on Blairs Ferry Road at the distant edge of the storm, located just west of the city of Ames and central Iowa. iPhone 11 camera.

8:51 pm. Set up now for spotting operations at Noelridge Christian Church (42° 2'59.42"N, 91°38'26.65"W) in Cedar Rapids, Iowa. Looking west. Distant approaching storm exhibiting a striated shelf cloud appearance.

8:55 pm. Shelf cloud/gust front now dominates the horizon. My spotting vehicle is in the foreground. iPhone 11 camera.

 

9:00 pm. Panorama of shelf cloud as it grows ever nearer. 

9:00 pm. Same image (less wide).

Radarscope image corresponding to 9:01 pm, with my location shown as the blue target icon.

9:02 pm. Shelf cloud looking due west.

9:04 pm. Looking southwest. Leading edge of shelf cloud is brightened by lights from a nearby commercial area.

9:04 pm. Looking north at leading edge of approaching gust front. 

Radar image for 9:04 pm. White arrow points from my position to a tornado-warned area just east of Independence, Iowa in Buchanan County.

9:05 pm. Image corresponding to radar above it. Note the pronounced striations in the shelf cloud, the tornado-warned lowering behind the taller tree in the distant background, and the possible clear slot at lower left. A clear slot is an intrusion of drier air from Rear Flank Downdraft (RFD). I estimated and reported maximum wind speeds at this location of up to 70 mph. At 9:15 pm I witnessed flashes from an unseen substation to my northwest, resulting in an immediate power outage to the neighborhood. Nikon D7200 DSLR camera.

Storm reports from KGAN Channel 2 website.

This storm met the National Weather Service criteria for a "derecho." A derecho is defined as a long-lived wind storm producing damage over a swath of 400 miles in length. Derechos produce wind gusts of 58 mph or greater with frequent gusts of 75 mph-plus.