Sonic Boom Heard In Fond du Lac. More May Be On The Way

Around 3PM Tuesday, August 9, 2023, residents throughout the City of Fond du Lac felt a rumble, and heard windows rattle in their house. Many thought something in the city had blown up and a few called 911. So what was it?

The annual ‘Northern Lightning’ training exercise for National Guard pilots is going on in the skies above central Wisconsin.

Based out of Volk Field, about 10 miles southeast of Tomah, military fighter jets and planes act out training situations.

The training this year is taking place August 7 – 18. The area is generally from a Fond du Lac and Appleton to Eau Claire area.

Throughout the last two days, you could hear an almost constant distant rumble in the sky coming from the jets. One today just got a little faster than they should have and broke the sound barrier.

A sonic boom forms when shock waves being emitted from the jet that usually fan out as smaller waves, build up as the jet travels the speed of sound. As the jet turns, or pulls up, that collection of smaller shockwaves that have collected to form one big shockwave, eventually hits the ground. When it does, the sound creates an explosion sound.

Compare it to a boat in the water. If a boat travels 5 miles per hour, and a wake wave moves out in front of the boat at 10 miles per hour, the wake wave will have a forward progress of 5 miles per hour relative to the boat. If the boat travels 10 miles per hour however, the wake wave will not have a chance to move out ahead of the boat as it and the boat are moving the same speed. The water will build up causing a larger wave riding along at the front of the boat. If the boat makes a sudden turn, or slows down, the larger, built-up wave will continue forward and if it hits land soon after, it will hit as a large wave.

In 1973, the Federal Aviation Administration banned supersonic commercial flights over land because of sonic booms and the negative impact they have on people and animals on the ground, however for the purpose of military training, there is some leeway given to the pilots who may cause a sonic boom from time to time.