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December Derecho produced a lot of firsts
In the Driftless Region
Tornados associated with December Derecho

DRIFTLESS - The December Derecho that impacted a huge swath of the nation, and the Driftless Region, produced a lot of ‘first ever’ records. Those included first ever tornadoes documented in the month of December for the National Weather Service-LaCrosse (NWS-LAX) viewing area, largest single-day tornado outbreak, most tornadoes in a single month, and most tornadoes recorded in one calendar year. 

It also included the warmest December temperatures ever recorded, with Boscobel setting a record at 72 degrees.

There was no previous record to break regarding December tornadoes, but the rest of the ‘firsts’ smashed previous records. The previous record for single-day tornado outbreaks was 13, set on June 8, 1993. On December 15, 2021, 27 tornadoes set down in the NWS-LAX viewing area, more than double the previous record. 

The previous record for most tornadoes in a single month was 16, set in June of 2004. The previous record for most tornadoes in one calendar year was 22, set in 1994. As of December 15, 2021, there had been 37 documented tornadoes in the NWS-LAX viewing area.

Prior to the 2021 event, there had been three months in which no documented tornadoes had occurred in the NWS-LAX viewing area. Those months were December, January and February. Now the list of months in which there has been no tornadoes is down to January and February. Not only that, but the total number of 27 is more comparable, according to records for 1950 to present) to March (20), September (37) or April (39). In the month of November, there have been three documented tornadoes, and in October, 13.

In other states, the 63 tornadoes that set down in the State of Iowa on Dec. 15, 2021 set the record for the most in a single day. That number nearly doubled the previous record of 35, set on August 31, 2014. In Minnesota, it was the fourth most tornadoes in a single day at 22, with the record being 48 on June 17, 2010. In Wisconsin it was the 17th most at nine, with the record of 27 being set on August 18, 2005.  

Nationally, the total outbreak of tornadoes associated with the Dec. 15, 2021 storm was the fourth most in the nation at 118. The record of 362 was set on April 27, 2011.

Storm description

The December Derecho event that swept through our area on December 15, 2021, was actually two separate weather phenomena. The first was a brief, fast-moving line of thunderstorms that was responsible for producing the tornadoes. The second was several hours of sustained, very strong winds.

Dust/smoke between fronts December Derecho
THIS IMAGE shows the view from satellite of the dust and smoke that travelled between the two waves of storms on December 15, 2021.

In between the two storms was an area visible by satellite of dust and smoke from wildfires in Colorado and Kansas that at times reduced visibilities to three-to-five miles. While most people likely heeded the warnings and stayed indoors, if you had ventured out that night between the two storms, meteorologists report that you would likely have encountered dust and been able to smell the smoke.

In all, in the NWS-LAX viewing area, the first storm produced four EF2 tornadoes, 14 EF1 tornadoes, and nine EF0 tornadoes.

In total, for the storm as it tracked out of Colorado, through Kansas and Nebraska, and then into Iowa, Minnesota and Wisconsin, there were a total of more than 2,000 storm reports. Of those, more than 1,000 were for non-thunderstorm wind damage or high gusts; 530 were for thunderstorm wind damage or high gusts, tornadoes or hail; 40 for wildfire smoke or a dust storm; and 450 for snowfall, mainly in areas to the west.

Follow up challenges

Since there have never been tornadoes in the time of year most people understand as ‘winter,’ meteorologists were never confronted with the particular challenges of surveying and documenting tornadoes in that season before.

The storms themselves presented a considerable challenge because they were fast-moving, travelling at 60-70 miles-per-hour, and the tornadoes were short-lived, many lasting just a few minutes. Because the hours of daylight in December are so short, most of the storms occurred under cover of darkness. The tornado touchdowns were also widespread over a large area versus clustered.

In following up on the storms after the event, meteorologists encountered many challenges they wouldn’t have at a different time of year. First, the lack of green vegetation made it harder to spot where there had been damage. Satellite imaging was hampered by clouds, and snow cover on the landscape. 

Technology, such as iPads would at times cease to function in the cold temperatures the survey teams encountered after the fact. And, surveying was delayed due to staffing shortages in the holiday season. 

The terrain of the Driftless Region actually created more complicated wind patterns than those seen in flatter areas, and in some cases, the efficiency of clean up efforts after tornadoes removed damage patterns crucial to accurate survey work.