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Something Wild: What ingredients go into summer thunderstorms?


This episode originally aired in June 2015 and was produced by Andrew Parrella.

Summer in New Hampshire brings those triple-H days: hazy, hot and humid. On days like that, there’s nothing more welcome than the arrival of a late afternoon thunderstorm — leaving in its wake cool, refreshing air, scrubbed clean of haze and pollution.

What is a thunderstorm?

Credit Courtesy J. Triepke via Flickr/Creative Commons

Three main ingredients that go into a good thunderstorm: unstable air, moisture and lift.

And in New England, summer is the time when humid, tropical air from the south often bumps into much cooler and drier air from Canada. Wherever two air masses meet, you’ll find unstable air. And when the warm and cold air masses collide, the denser cold air wedges itself underneath the warm air and lifts it up. (That also contributes to the humidity that makes us feel so miserable.)

As the humidity (or moisture) rises through the atmosphere, it cools: about 5 degrees for every 1,000 feet of altitude. The water vapor soon condenses and forms cumulonimbus clouds, from the Latin “cumulo” meaning heap or pile and “nimbus” meaning dark cloud. The rising humidity continues to condense and eventually forms water droplets that are too heavy to be lifted further by rising air currents. So they fall as rain. 

Ice in summer

Credit Courtesy Alexey Kljatov via Flickr/Creative Commone;

Sometimes those cumulonimbus clouds keep rising and run into below-freezing temperatures.

Water in cumulonimbus clouds often moves around as super-cooled liquid or in a frozen state. Most rain in thunderstorms starts out as snow, even on the warmest summer days. And sometimes it is still frozen when it gets to the ground.

Hail develops when frozen droplets go round and round in storm clouds, accumulating mass until they are too heavy to stay in the air. Then they fall to the ground. 

A little flash goes a long way
This image illustrates how lightning seeks out different roots on the ground.

It’s not a thunderstorm without the flash of lightning. That flash comes from friction: the friction between tiny ice and water particles rubbing together generates static electricity, much like rubbing your socks back and forth on a carpet.

The smallest particles rise to the top of the storm cloud and pick up a positive charge. Falling rain and hail in the cloud strips rising water droplets of their electrons, accumulating a negative charge at the bottom of the cloud. This draws positive charges into tall objects on the ground — like boat masts, pine trees and, sooner or later, that results in a flash.

Meteorologists estimate that lighting strikes the Earth 100 times a second.

Calm after the storm

On hot days, the heat and humidity just build and build — until it’s hard to breathe, and most of us don’t even want to move. Then, just when you can’t take anymore, the sky explodes!

When the storm passes, the sun comes out shining through cool, dry, rejuvenating air. Sometimes, after the storm, you can actually see the individual trees on a ridge that were completely hidden by hazy air before the storm. Enjoy nature’s light shows this summer.

Something Wild is a partnership of New Hampshire Audubon, the Forest Society and NHPR. It is produced by the team at Outside/In.

Naturalist Dave Anderson is Senior Director of Education for The Society for the Protection of New Hampshire Forests, where he has worked for over 30 years. He is responsible for the design and delivery of conservation-related outreach education programs including field trips, tours and presentations to Forest Society members, conservation partners, and the general public.
Chris Martin has worked for New Hampshire Audubon for over 31 years as a Conservation Biologist, specializing in birds of prey such as Bald Eagles, Ospreys, and Peregrine Falcons.

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