December Derecho

This is December 15 in Iowa?? A 12:38 am CST Public Severe Weather Outlook (PWO) posting by The National Weather Service (above) shows an area of forecasted severe weather later in the day on Wednesday, December 15, 2021. The red area is for a Moderate Risk, a foreboding severe weather designation which is practically unheard of at this time of the year in this part of the country. 

A mature line of severe storms in eastern Nebraska and Kansas were already well in progress at the time of this radar screen capture from 3:05 pm. The white arrows indicate storm movement, the target icon at right is my location.

3:30 pm. My home weather station shows the eye-popping numbers of the sultry nature of current outside weather conditions.

4:04 pm. Looking east from Bowman Woods Park in Cedar Rapids, Iowa. Clouds have a definite spring-like appearance. A nearly-full moon peeks from behind some cirrus at upper left. 

4:45 pm. Ominous SPC categorical convective outlook (left panel), and tornado outlook (right panel) postings.

Tornado Watch 565 goes out for areas of eastern Iowa, southeastern Minnesota, western Wisconsin and northwestern Illinois, valid from 5:30-11:30 pm.

5:44 pm. Radarscope screen capture. Lit-up line of storms with tornado and severe weather warnings continuous from north to south in the state, west of Des Moines. My name and amateur radio call sign can be seen at right.

7:11 pm. Mesoscale Discussion 2036 is posted, with the likely potential for damaging wind gusts and tornadoes shown in the highlighted area.

7:43 pm. Radarscope screen capture. Approaching severe-warned storm is now forming a tight and well-defined linear appearance west of Cedar Rapids and to the south. 

8:00 pm. Approaching line of storms is approaching my position at Bowman Woods Park in Cedar Rapids.

8:15 pm. Looking west at approaching severe weather. Sirens had sounded. Tree tops and clouds are blurred in these images due to high winds and using a one second shutter exposure to capture what little light was available. Wind speeds peaked here in the estimated 60-65 mph range.

8:19 pm. Similar capture. Nikon D7200 DSLR camera. 

Aircraft avoided this massive storm. Shown above is the Flight Aware flight path for United Flight 406, from Denver (left) to New York on December 15. The aircraft departed Denver at 4:12 pm (MST), and arrived in New York at 9:50 pm (EST). Note the significant flight deviation south of the storm!

KCRG TV-9 tornado track map (as of December 22, 2021). 

Cedar Rapids temperatures on this day (high of 73 degrees F) shattered old records. The former high temperature for December 15 was 55 degrees F (1957), and the former high temperature for all of December was 69 degrees F, observed on December 4, 1998. The December 15, 2021 storm was later classified as a "serial derecho." with 43 confirmed tornadoes surveyed by the NWS. That number eclipsed the all-time previous daily high of 30, set on August 31, 2014. This was the first time a derecho has occurred anywhere in the country during the month of December. Also records from the storm was the 55 recordings of 70 mph or higher wind gusts, and 17 of the tornadoes rated EF2 or stronger, breaking the previous mark of 16 on June 7, 1984.