In a study that could enhance weather forecasting, Utah researchers discover that how snowflakes move is astonishingly predictable.

Tim Garrett

Tim Garrett has devoted his scientific career to characterizing snowflakes, the protean particles of ice that form in clouds and dramatically change as they fall to Earth.

Now the University of Utah atmospheric scientist is unlocking the mystery of how snowflakes move in response to air turbulence that accompanies snowfall using novel instrumentation developed on campus. And after analyzing more than half a million snowflakes, what his team has discovered has left him astonished.

Rather than something incomprehensibly complicated, predicting how snowflakes move proved to be surprisingly simple, they found.

“How snowflakes fall has attracted a lot of interest for many decades because it is a critical parameter for predicting weather and climate change,” Garrett said. “This is related to the speed of the water cycle. How fast moisture falls out of the sky determines the lifetime of storms.”

“Letters sent from Heaven”

The famed Japanese physicist Ukichiro Nakaya termed snow crystals “letters sent from heaven” because their delicate structures carry information about temperature and humidity fluctuations in the clouds where crystal basal and prism facets competed for water vapor deposition.

While every snowflake is believed to be unique, how these frosty particles fall through the air—as they accelerate, drift and swirl—follows patterns, according to new research by Garrett and colleagues in the College of Engineering. Snowflake movement has important implications for weather forecasting and climate change, even in the tropics.

“Most precipitation starts as snow. How the question of how fast it falls affects predictions of where on the ground precipitation lands, and how long clouds last to reflect radiation to outer space,” Garrett said. “It can even affect forecasts of a hurricane trajectory.”