Jim Steenburgh's favorite storms blow in from the Northwest.

"They are great for meteorology and great for skiing," wrote the University of Utah professor of atmospheric science on his blog as he geared up for a mid-November storm. Northwesterly systems scrape across the Great Salt Lake, scooping up moisture on their way to the canyons above the Salt Lake Valley, where it returns to land as Utah's famous powder. Or sometimes as less-than-great rain or wet snow.

Knowing what happens to precipitation as it moves across the sky and back to earth will help scientists better understand the forces behind Utah's winter weather, according to Steenburgh's graduate students. For a month this fall, they chased weather around northern Utah with mobile Doppler equipment that will let them record "meteorological CAT scans" of storms as they unload moisture on the mountains.

"It's important for seeing the melting levels so you can see where the snow is melting and transitioning to rain," Steenburgh said during a recent demonstration at Salt Lake City's Hillside Middle School. This data are crucial to predicting how much snow will fall in a particular place.

The Center for Severe Weather Research, a nonprofit based in Boulder, Colo., provided the truck-mounted radar, called Doppler on Wheels, or DOW, to the U. through Nov. 21 for educational purposes.

"We are getting the opportunity on down days to take it to schools and get kids excited about science," said graduate student Christy Wall. The team visited at least a half-dozen schools, demonstrating how Doppler works for as many as 500 students. The rig, one of three traveling the nation, is designed for measuring tornadoes.

But Steenburgh's crew has found it ideal for gathering data they would not otherwise be able to obtain about Wasatch micro-weather.

He is particularly interested in understanding the size and shape of precipitation particles and how they flatten, grow and break apart as they fall.

"Unlike radars used for weather forecasting, the Doppler on Wheels can be placed anywhere during a storm, enabling us to peer into storms and uncover their secrets," Steenburgh said. Because fixed-position Doppler directs its radar upward, it can provide little resolution close to the ground.

"With DOW, the radar is oriented horizontally and vertically, so we see the low-level processes happening in the storm that you wouldn't see with conventional Doppler," said Jon Zawislak, a doctoral candidate at the U. "We can take the small-scale processes to better understand the physical processes, then take that and improve the models [for forecasting weather]."

A northwesterly storm forecast to drop up to a foot of snow in the Wasatch earlier this month prompted Steenburgh's students to deploy the blue rig with its six-foot radar dish near Daybreak in southwestern Salt Lake County, with an uninterrupted view straight up Little and Big Cottonwood canyons.

Doppler requires clear lines of sight, uncluttered with trees and buildings, to provide useful data of ground-level weather, and not many places offer that. The team pre-selected such sites on the Bacchus Highway, Saratoga Springs and Daybreak to conduct observations, depending on where the weather was coming from and what they hoped to observe, Zawislak said.

The team spent the night of Nov. 4-5 on State Route 111 on the west side of the Salt Lake Valley, observing a storm as it dumped several inches of snow on nearby cities.

"The whole experience has been completely amazing," said Wall, who hails from tornado country. "I did my undergraduate degree at the University of Oklahoma, and those trucks are in Oklahoma all the time, but in my entire four years of college I never got to touch one."

Wall's research interest is tropical heat convection, but using this gear to study snow is advancing her scientific ambitions.

"I don't know anyone in graduate school who gets this opportunity," she said. "Being able to see the radar and operate it makes it easier for me to interpret the radar data I see in my research. If you have this experience and have this confidence, it makes you more valuable in field campaigns."

bmaffly@sltrib.com —

Doppler on Wheels

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