Utah’s famous mountains can wring a lot of snow from even low-moisture storm systems, according to new U research.

February 6, 2024

Jim Steenburgh displays a device for measuring snowfall. Credit: Brian Maffly ^^ Banner photo above: Little Cottonwood Canyon. Credit: UDOT.

Major snowstorms in Utah’s Wasatch Mountains are both a blessing and a curse. They deliver much-needed moisture that supplies water to the state’s biggest metropolitan area and fluffy light snow to support the world’s finest powder skiing.

But heavy snowfall also wreaks havoc on canyon roads and creates extreme avalanche hazards that can sometimes shut down busy winter recreation sites.  Alta at the head of Little Cottonwood Canyon, for instance, can be reached by vehicle only via a winding road that rises 3,000 feet in 8 miles, crossing about 50 avalanche paths.

University of Utah atmospheric scientists have set out to better understand extreme snowfall, defined as events in the top 5% in terms of snow accumulations, by analyzing hundreds of events over a 23-year period at Alta, the famed ski destination in the central Wasatch outside Salt Lake City. The resulting study, published this week in Monthly Weather Review, illustrates the remarkable diversity of storm characteristics producing orographic snowfall extremes in the ranges of the Intermountain West.

The orographic effect occurs when air is forced to flow up and over mountains, which cools the air and condenses its water vapor.

Some of the new findings surprised researchers. For example, they looked for an association between heavy snow and a weather factor called “integrated vapor transport,” or IVT, but found a complicated relationship.

“IVT is essentially a measure of the amount of water vapor that is being transported horizontally through the atmosphere, said lead author Michael Wasserstein, a graduate student in atmospheric sciences.  “In certain regions high IVT can produce extremely heavy precipitation. That can be the case for the Wasatch, but not always.”

In the West Coast’s Sierra Nevada and Cascade Range, by contrast, there is a stronger relationship between high-IVT storms blowing in from the Pacific and extreme precipitation and snowfall.

Spanning the years 2000 to 2022, the study, which was funded by the National Science Foundation, analyzed a total of 2,707 snow events, each covering a 12-hour period. The average amount of snow deposited during each event was 11.2 centimeters (4.4 inches), while the median amount was just 7.6 (3 inches). Alta ski patrollers did much of the data collection at the monitoring station located near the ski area’s Wildcat Lift.

The researchers homed in on “extreme” events above the 95th percentile, or 138 storms in which 30.5 centimeters (12 inches) or more snow fell. “Those would be snowfall rates of about an average of an inch an hour,” said Jim Steenburgh, the study’s senior author. The biggest 12-hour accumulation was 65 centimeters (26 inches), recorded on March 30, 2005.  They also examined “extreme” water-equivalent snowfall events above the 95^th percentile, or 116 storms with at least 27.9 mm (1.11 inches) of water equivalent precipitation. The water equivalent of precipitation measures the amount of water in the snowfall and is important for water resources and avalanches.

You might not initially think of fog as a form of severe weather, but when fog sets in and visibility plummets, transportation becomes dangerous.

Zhaoxia Pu

Fog is the second-most-likely cause of aircraft accidents after strong winds, but despite the high impact of fog events and a long history of research, fog prediction remains a long-standing challenge for weather prediction because of complex interactions among the land surface, water, and atmosphere. There’s still a lot of fundamental things about fog that we don’t know.

Zhaoxia Pu, University of Utah professor of atmospheric sciences and Eric Pardyjak, professor of mechanical engineering, hope to change that through a field campaign and scientific research using Utah’s Heber Valley as the laboratory.

For about six weeks, from 7 January to 24 February 2022, Pu, Pardyjak and their colleagues, including scientists from the National Center for Atmospheric Research (NCAR) and the Environment and Climate Change Canada as well as graduate students and undergraduate students from atmospheric sciences and mechanical engineering at the University of Utah, watched a network of sensors on the ground in the Heber Valley along with comprehensive sets of instruments from the NCAR's Erath Observing Laboratory and satellite observations. The valley is bounded by mountains, relatively flat in the basin and features two lakes — Jordanelle and Deer Creek reservoirs. Its conditions, Pu says, are representative of mountain valleys around the world.

On winter nights, cold air pools on the valley floor and creates favorable conditions for several forms of fog, including cold-air pool fog, ephemeral mountain valley cold fog and radiative ice fog. By observing how these different kinds of fog form and dissipate, the researchers are continuing to learn about the meteorological conditions and physical processes governing the formation of fog and improve fog prediction.

The study is funded by a $1.17 million grant from the National Science Foundation.

Now, in a recent paper in the Bulletin of the American Meteorological Society, Pu and her colleagues have published findings via The Cold Fog Amongst Complex Terrain (CFACT) project, conceived to investigate the life cycle of cold fog in mountain valleys.

The overarching goals of the CFACT project, according to the paper’s abstract, are to 1) investigate the life cycle of cold-fog events over complex terrain with the latest observation technology, 2) improve microphysical parameterizations and visibility algorithms used in numerical weather prediction (NWP) models, and 3) develop data assimilation and analysis methods for current and next-generation (e.g., sub kilometer scale) NWP models.

Field observations, NWP forecasts, and large-eddy simulations provided unprecedented data sources to help understand the mechanisms associated with cold-fog weather and to identify and mitigate numerical model deficiencies in simulating winter weather over mountainous terrain. The paper summarizes the CFACT field campaign, its observations, and challenges during the field campaign, including real-time fog prediction issues and future analysis.

Comprehensive measurements

A network of ground-based and aerial in situ instruments and remote sensing platforms were used to obtain comprehensive measurements of thermodynamic profiles, cloud microphysics, aerosol properties and environmental dynamics. Over its seven-week course, the CFACT field campaign collected a diverse and extensive dataset, including high-frequency radiosonde profiles, tethered balloon profiles, remotely sensed thermodynamic and wind profiles, numerous surface meteorological observations, and microphysical and aerosol measurements. Nine intensive observation periods (IOPs) explored various mountainous weather and cold fog conditions.

Despite the drought in the western United States in 2022, which limited the occurrence of persistent deep fog events associated with persistent cold-air pools that regularly form in higher-elevation Intermountain West basins, the campaign observed highly spatially heterogeneous ephemeral fog and ice fog events. Since ephemeral fog and ice fog are extremely difficult to detect, model, and forecast, CFACT provided unprecedented datasets to understand both types of fog and validate the NWP model.

Meanwhile, the variety of non-fog IOPs provided valuable observations for understanding near-surface inversion, ice crystal formation, moisture advection and transportation, and stable boundary layers over complex terrain, all of which are essential factors related to fog formation. Comprehensive studies are ongoing for an improved understanding of cold fog over complex terrain.

Dr. Kevin Perry, an atmospheric scientist at the University of Utah, is one of the scientists working to save the Great Salt Lake from drying up.

The lake needs all the help it can get—informing citizens and policymakers on the science of the lake is critical to keep it going for years to come. Lately, Perry says more of his time is spent communicating about his research than actually doing it.

In 2021, Perry presented the findings of a two-year research project to determine the contents of the dust coming off of the dried Great Salt Lake surface. He found that not only was the dust a source of pollution, but it also released toxic chemicals like arsenic and other heavy metals into the air. The potentially harmful air pollutant would only worsen if the lake wasn’t restored—and he’s been trying to get Utahns to listen ever since.

While Perry was out buying groceries, a cashier struck up a conversation with him about the Great Salt Lake. The cashier said he had created a website to warn community members about dust pollutants coming off the Great Salt Lake and started to explain the risk of the exposed lakebed to Perry.

“I laughed and I said, ‘You don’t know who I am, but you know the toxic dust that you’re talking about? That’s my scientific research,’” Perry says. “That kind of blew me away…when [I saw] somebody who has no scientific background was inspired enough to spend their time and effort trying to save the Great Salt Lake.”