Understanding wintry mix

Researchers head north for insight into near-freezing weather, mixed precipitation events

By Zachary Matson 

As a weather balloon floated higher and higher above the old Clinton County airport in Plattsburgh last month, Bin Han, a post-doctoral fellow at the University at Albany, tracked a stream of data from a computer on the ground.

The data transmitted from an instrument dangling from the balloon showed air temperature, wind speed, pressure, humidity and other key measures of atmospheric conditions as it disappeared into a slate gray sky. 

The balloon can climb for over an hour and reach heights of nearly 70,000 feet before it expands under pressure and eventually pops, Han said. 

Air temperatures cooled as the balloon increased its altitude, but they then warmed in a thin layer of the atmosphere before starting to cool again. The temperature inversion showed up on Han’s screen as an abrupt reversal in the curve of otherwise-cooling temperatures.  

“It’s an interesting structure for winter precipitation,” Han said.  

Han and UAlbany graduate student Matt Brewer were stationed at the former airstrip as part of a team of researchers studying freezing rain, sleet, hail and their variations across the Lake Champlain and St. Lawrence River valleys, an area that receives the most mixed precipitation in North America. Teams fanned out to collect data from three other sites that day, on both sides of the international border. 

The dynamics of the pocket of warm air can teach scientists a lot about precipitation types that confound meteorologists and commuters alike. When ground temperatures hover around 32 degrees, the precipitation that hits the ground can take the form of rain, ice, sleet, hail snow or a mix of precipitation types. Small differences in atmospheric conditions can result in dramatically different weather on the ground. 

In February and March, the research team composed of scientists from UAlbany, University of Colorado, University of Wyoming and Canadian institutions collected data during 11 separate storms. The team relied on the types of weather balloons Han released in Plattsburgh and other on-the-ground ways to measure precipitation types, as well as mobile radar trucks built to endure tornadoes and wildfires and a specialized Canadian airplane outfitted with scientific instruments.

During one storm studied during the project, a shallow layer of warm air created an inversion a few hundred feet from the ground.

“If you were to go up to the top of a skyscraper, you would be up in the warm air, it was that shallow,” said Justin Minder, a UAlbany atmospheric scientist and the lead investigator of the WINTRE-MIX research project. “The elevated warm layers are really important, because they can cause snow to melt and as it falls in the cool level closer to the surface, it can refreeze into sleet…They are difficult situations for our computer models to handle.”

Near-freezing weather events rank among the hardest to forecast. The stakes are high, too. Mixed precipitation storms are critical to road safety, and they complicate decisions around school closures, winter road management and daily commutes. By studying a range of storms, researchers hope to develop a stronger understanding of the fundamental conditions that influence mixed precipitation weather events and improve their predictive models.   

“We hope to translate some of our results into forecasting advancements,” Minder said. 

During one storm, Han’s team collected data from Essex Farm inside the Adirondack Park. The weather was less mixed than it was a full snow storm. Han, who grew up in China and studied at Nanjing University before getting the UAlbany fellowship, had never encountered an Adirondack snowstorm. “I’ve never seen that much snow in my whole life,” Han said.

The six-week field campaign was focused on collecting as much data as possible, focusing on a variety of storms and weather patterns that could offer insight into mixed winter precipitation. Now, researchers are shifting to processing and analyzing the data, which will last another three years. Data collected during the field campaign will be posted publicly within a year. Minder said he expected researchers to publish papers overviewing the project and their broader findings before people analyzed into more discreet topics. 

“It benefits science as a whole if as many people as possible can easily access the data and use it in their research,” Minder said. 

In early March, As Han and Brewer waited at the site for the next balloon release – once every two hours – they checked in on Cameron Smith, who was operating the mobile radar. Inside the truck housing the radar, Smith sat before a bank of nearly a dozen monitors, each one showing a different view of the sky. Scanning the sky at different angles, the radar funneled another stream of data for later analysis. 

“You are seeing some stuff, it’s light rain,” said Smith, who came to the region with a team from Colorado that operated the radar systems.

While research crews in Quebec were documenting freezing rain, conditions stayed mostly dry in Plattsburgh throughout the morning. As air flows move up the Lake Champlain valley from the south and collide with flows across the St. Lawrence valley, they can create heavy storms, particularly north of the St. Lawrence River. The Adirondacks, though, will often create a rain shadow to their immediate north.  

“As winds come over the Adirondacks and blow down into the Champlain Valley, down into the St. Lawrence Valley, they would really suppress the precipitation,” Minder said. “You can see this big hole of precipitation just downwind of the Adirondacks.”