Can You Smell Rain Coming?

January 29, 2019
Can You Smell Rain Coming?

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Have you ever wondered why we can smell the rain coming? 

My grandfather could even track squirrels with his sense of smell. What he was best known for, however, was his incredible nose for weather.

He could tell a storm was approaching before anyone else in the county. One of my father’s earliest memories was running to warn neighbors that bad storms were coming so that they could get things covered.

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Most of us have smelt approaching storms. Source: Wikipedia

Most of us have probably smelt that lovely fresh, earthy aroma of an approaching rain storm. He could smell it coming and even warn people about the strength and likelihood of tornadoes. (He went nuts once when he smelt a hurricane coming.)

He was an educated man (and became superintendent of the Vanderbilt, Texas school system) but the most educated part of him was his nose. In an era when radio coverage was spotty, especially in the country, the neighborhood practically thought of him as a medicine man.

Now scientists have discovered why people can smell the storms so far away. A sensitive snout is smelling ozone, petrichor and geosmin; in other words, the nose smells oxygen, the debris that raindrops kick up and wet bacteria.

First comes the ozone, the oxygen fried by lightening that changes its chemistry for O2 to O3. This has a sweet, pungent zing and winds carry it down from the upper atmosphere to your waiting nose. If you smell a lot of that—look out!

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Ozone is produced by lightning, including this monster strike. Source Wikipedia

Then comes the raindrops. Scientists discovered that water drops hitting surfaces like soil or leaves knock particles up in the air. A raindrop hitting an uneven surface traps bubbles of air that shoot upwards and burst from the top of the water droplet like fizz in a champagne glass. These bubbles can float long distances before they pop and you can smell the pollens, dirt, oils or city scum. Nature’s champagne is called petrichor.

Finally, the wet soil triggers the bacteria or blue-green algae to release geosmin, that great earthy smell so loved by gardeners. 

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Drops of water spray aerosols into the air that you can smell downwind. Source: Wikipedia

That explains why my grandfather’s educated nose could smell approaching storms. How he tracked those squirrels through the woods remains a mystery.

About This Blog

Are you a weather watcher? Welcome to “Weather Whispers” by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather—from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these articles. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.

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