Scientists and graduate students working through Storm Peak Laboratory at the top of Steamboat Resort has examined 45 years of snowstorm data to identify what conditions cause the “big dump” days at the ski area.

The “biggest powder days” happen when the snowflakes form during storms between minus-3 and 10 degrees Fahrenheit, said Gannet Hallar, Ph.D., director of Storm Peak Laboratory. The wind direction on these big snowfall days is primarily from the northwest with higher wind speeds of up to approximately 20 mph, Hallar said.

In general, conditions that cause the big powder days at Steamboat Resort come from fast, windy and colder storms from the northwest with temperature ranges that create a stellar dendrite type of snowflake. According to the National Avalanche Center, “stellar dendrites are what most people think of when they picture a snowflake” and “resemble a star with six arms extending from their center.”

Hallar provided a presentation about the study of 45 years of snowstorm data leading to big powder days as part of the annual Yampa Basin Rendezvous hosted May 28-29 in Steamboat Springs and sponsored by 11 nonprofit, environmental and educational organizations.

“Using historical data from Steamboat Ski Resort of new snow accumulation depth collected from 1979 to 2024, the extreme snowfall events (95% percentile) were investigated,” Hallar said of the study of the top 5% of powder days based on inches of accumulation.

Hallar said colder temperatures of approximately -3 to 10 F is the range where the large stellar dendrites snowflakes form, and these low-density snowflakes grow very quickly.

“What makes stellar dendrites unique is that they occur when the snow grows very, very quickly in a very short period of time, so they grow fast,” Hallar told the large audience. “They grow much, much faster than other habits of snowflakes. So, we call them the speedy snowflakes.”

The professor said the amount of snow received in a snowstorm is impacted by how much moisture is in the air, what the ground terrain looks like where the storm travels and the temperature of the storm as it is happening.

“You can think about snowflakes as a thermometer of the atmosphere,” said Hallar, a professor in the University of Utah atmospheric sciences department. “Snowflake shape and size depends on temperature.”

The professor said the scientists are looking at how climate change may impact big powder skiing days.

“What could be the impact of climate and climate change with warmer temperatures that we are observing on our snow?” Hallar said. “Could we be moving from one regime to another regime where we go from the deep, dry powder days to a more liquid precipitation extreme. I don’t think we have an answer for you yet, but we are starting to look at trends that are suggesting that might be happening in the long-term record.”

Much of the work on the snowfall data study was completed by Anne Lang, a graduate student in atmospheric sciences at the University of Utah, who agrees that big snowfall days may become increasingly at risk.

“One hypothesis is as we move to higher temperatures, we are having less events in this temperature range that we have now and that could lead to less extreme powder events,” Lang said.

The big snowfalls that hit Steamboat Resort generally come in quickly toward Mount Werner from a 45-degree angle on a path roughly from over the Elkhead Mountains and toward Elk Mountain, known locally as Sleeping Giant.

The scientists hypothesize that the Elkhead Mountains at more than 10,800 feet as well as Elk Mountain at 8,727 feet in elevation initiate orographic lift causing air to rise and cool quickly — enhancing condensation and producing more snow.

Those terrain features “combined with high wind speeds and perfect temperatures allow for the dendrites to form, falling at the resort,” Hallar said.

Graduate student Lang joined the study group due to her interest in extreme snowfall events that have impacted people and caused deaths in her home country of Austria.

“Studying extreme snowfall events is important because those are the events that impact society the most, and winter storms can be associated with a lot of different dangers such as avalanches, landslides and flooding,” Lang noted, as well as impacting water resources.

Storm Peak Laboratory is an internationally recognized high-elevation atmospheric research station located on the west summit of Mount Werner at 10,532 feet near the top of the Morningside chairlift. The lab staff has recorded measurements since 1981 at its high elevation location and since 1979 at the resort, Hallar said.

The current permanent building includes a full chemistry lab and instrumentation lab. Some 100 university students use Storm Peak Lab for research training each year.

Hallar also is part of a team of scientists that will continue to learn more about mountain snow forecasting aided by results from this past winter’s Snow Sensitivity to Clouds in a Mountain Environment study conducted in Routt County. That work was conducted by dozens of students and professors from seven educational institutions in a three-year, $4.8 million study funded by the National Science Foundation.

“The goal here is to really improve our weather forecasting,” Hallar said. “We are trying to understand how snow forms in this valley and how we can improve predictions throughout the entire western United States.”