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It's Raining Cats, Dogs, and Bacteria! a sweltering summer's eve lit faintly by the glow of the setting sun, there's naught more refreshing than a light summer rain. As dusk turns to dark, reinvigoration becomes relaxation as the soft pitter-patter of raindrops on windows ease the transition from wakefulness into a restful night's sleep.

What can we thank for picturesque moments of precipitation like this one? Give your gratitude to evaporation and cloud formation, but don't forget bacteria.

That's right, bacteria.

A growing agglomeration of research is now showing that bacteria whipped up into the sky by winds can play a central role in forming snowflakes, raindrops, and hail across the globe.

For years, atmospheric scientists have understood that precipitation is formed when microscopic water droplets from clouds latch on to tiny dust particles. The water freezes around these ice nuclei, which then fall to Earth as rain, snow, or hail. But increasingly over the past four years, scientists are finding that bacteria, often Pseudomonas syringae, frequently play an identical role as dust particles in producing precipitation.

One of these scientists is University of Wyoming professor Gary Franc. From Storm Peak Laboratory, resting atop 10,500 foot Mount Werner in Steamboat Springs, Colorado, Franc literally spends his days up in the clouds studying precipitation-causing bacteria at the source.

"I'm sure there's a whole ecosystem in the sky going on that we are just getting an inkling about," he recently told the Laramie Boomerang.

Franc has also built further upon the mounting evidence that these bacteria actually enable water molecules to solidify above their normal freezing temperature. The organisms accomplish this by using a special substance that binds water molecules in an orderly arrangement conducive to forming ice particles.

"Basically, these bacteria have proteins that line up water molecules that mimic the crystalline structure of ice," Franc told the Laramie Boomerang.

Franc, and other scientists like Montana State University's David Sands and Louisiana State University's Brent Christner, all believe that research into these "rain-making" bacteria may furnish knowledge that could eventually aid drought-stricken areas across the globe.

The research could also be used to modify the good old idiom, "When it rains, it pours."

Because when it rains, it occasionally pours bacteria.

(Image: Bob Jones, Geograph)