Weather 102: Why is nighttime thunder so loud?

MWN friend Kristen Boyden asked a great question: "Why were Tuesday night's storms so loud?"

The overnight storms (and this is pretty common for nighttime storms and some during the day as well) were what we call "elevated thunderstorms." Basically, we had a very strong temperature inversion in place, in which the temperature rises with height rather than cooling. It was about 45° F at the surface during last night's storms, but 57° F at just 4,000 feet up! That inversion creates a stable layer in the atmosphere at the low levels and basically acts like a lid at 4,000 feet above us.

An atmospheric sounding (temperature/humidity profile) of the airmass over Memphis Tuesday night shows temperature (red line) increasing as you go up into the atmosphere, an inversion. That inversion "caps" the atmosphere below, trapping the sound of the thunder in the lowest few thousand feet. (NOAA/AMDAR)

When lightning discharges under that lid, the sound of the thunder is trapped close to the ground. Since the sound can't escape UP ↑, it bounces around between the ground and the stable layer above (the lid), amplifying the noise. It's like setting off firecrackers in grandma's pressure cooker!

Elevated thunderstorms occur when warm air overrides cooler air near the surface, creating a temperature inversion, and thus a stable layer of air in the low levels, above which convection occurs. (Graphic courtesy @wxbrad)

In addition, general daytime noise is reduced at night, so the thunder seems louder because the ambient noise level is quieter. (Like when your baby lets out a cry in the doctor's waiting room vs. in a house full of other kids!) I frequently say that thunder at night is often louder than during the day, but in fact, ELEVATED thunderstorms are truly the cause for the noise level. They just happen to occur more often at night! It doesn't mean they are "more severe" or even more damaging. They're just louder.

Erik Proseus
MWN Meteorologist

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