Dear Tom,

What would make a deep elongated metal vibrating sound of thunder? Twice on Monday August 29 my husband and I heard this strange sound coming from the sky that appeared to be a type of thunder and lasted like a rolling thunder.

Wendy Pogwizd, Shorewood

Dear Wendy,

Thunder is “the sound of lightning”. A bolt of lightning practically instantaneously heats the air to about 50,000 degrees. Such extreme heating causes explosive expansion of the air, followed by rapid cooling and contraction. That sets up sound waves that we hear as thunder. Those waves travel about 1 mile every five seconds. Lightning bolts are often 20 miles in length but occasionally much longer, and thunder is generated everywhere along the bolt’s path. You will first hear thunder from the part of the bolt nearest you, and then thunder from more distant portions, producing “rolling thunder.”