The National Weather Service office in Des Moinse has confirmed the December 15 storm system that brought high winds and tornadoes to Iowa and other parts of the midwest was also the first-ever derecho recorded in the month of December in the United States.
After consultation with the National Weather Service’s Storm Prediction Center in Omhama, it was determined the system was a ‘serial derecho’ rather than a “progressive derecho” like what hit the state in August 2020.
“Serial derechos develop along a line more parallel to the mid level flow and therefore are a much longer line of storms, however travel shorter distance,” according to the weather service.
“The overall wind profile contains more directional shear (turning winds with height) which creates smaller but more bow echoes and increases the chance of brief tornadic spin-ups. Serial derechos are overall easier to forecast due to the nature of the large scale system that typically creates them.”
While Muscatine was mostly spared by the derecho, other than a few scattered power outages and no serious damage, 21 tornadoes have been and one death have been confirmed in Iowa.
We've had several inquiries about December 15th's line of thunderstorms being classified a derecho. We have double checked with @NWSSPC, and 12/15/2021 meets the criteria for a Serial Derecho. This is bit different then what Iowa saw in August 2020.
— NWS Des Moines (@NWSDesMoines) December 20, 2021