‘It’s sort of like a cat-and-mouse game with the snowpack’: Avalanche forecasters explain their relationship with regional snows

MOLAS PASS — Each year, Chris Bilbrey becomes intimately acquainted with the snowpack of the San Juan Mountains to a degree generally unmatched by the outdoor enthusiasts who take to the range to frolic, slide and sled.

Bilbrey is one of seven forecasters for Colorado’s southern mountains with the Colorado Avalanche Information Center, and his job demands an intricate knowledge of snowy layers that sit below the surface.

The information center is a program within the state’s Department of Natural Resources and is the only avalanche center in the country that is part of a state agency. Beginning in early winter, the organization releases a detailed daily assessment of avalanche hazards and risk across the state.

This season, nine people have been buried in avalanches across the state; seven have died, including three in southwest Colorado this past weekend.

“It’s a storybook from the beginning to the end, and the narrative changes every time,” said Chris Bilbrey, a forecaster with the Colorado Avalanche Information Center. He gets to know individual persistent weak layers well throughout the season.
Reuben Schafir/Durango Herald

Authors of an evolving snowpack

After he deftly squares off the walls of a snow pit, Bilbrey pokes and prods layers in the snowpack; he identifies which of them resulted from specific dry periods, and connects others to individual storms.

Not unlike an archaeologist reads layers of sediment to construct a geologic narrative, Bilbrey does the same with snow, but with the added challenge of predicting how those deposits are likely to react to new precipitation.

In early February, a prolonged dry period left the snowpack vulnerable.

“It’s a storybook from the beginning to the end, and the narrative changes every time,” Bilbrey said. “Each chapter is subsequent to the next chapter. This dry period is like the calm before a battle with a new clan — before the next storm and weak layer.”

As is the case in many seasons, most of the state’s snowpack is plagued by a persistent weak layer. The bane of many backcountry skiers’ and riders’ existence, persistent weak layers form when a layer of snow has a poor bond to the fresher snow above it, allowing slabs of snow to break free, causing avalanches.

These layers can remain for months — hence the epithet “persistent” — and forecasters get to know each one well.

Bilbrey estimates he digs between 80 and 110 snow pits each year. He tests the pits to determine how hard each layer is, a scale that ranges from knife to fist hard as determined by the largest object that can penetrate the layer. Then, he runs a compression test to observe the stability of the snowpack, often followed by an extended column test to observe how easily fractures propagate across a slope.

But Bilbrey does not derive forecasts from his observations alone. Avalanche forecasts are the product of numerous factors, including weather forecasts, observed avalanches, observations submitted by the public and peer scrutiny.

“It’s like your own mental multivariate model,” he said.

Bilbrey’s week begins on Tuesday. He spends the full day in the field and does not have to produce a forecast. Instead, he heads to the mountains, armed, like a scientist, with a question and a hypothesis (Bilbrey has a master’s degree in snow and environmental science).

Chris Bilbrey, a forecaster with the Colorado Avalanche Information Center, digs a pit with Rebecca Hodgetts, southern mountains lead forecaster with the center.
Reuben Schafir/Durango Herald

Southern Mountains Lead Forecaster Rebecca Hodgetts said that having forecasters on the snow is a critical part of the process.

“We have a forecast model that we follow, but we lean super heavily on the regional people to tell us what’s going on,” she said.

Bilbrey stressed that having a firsthand feeling — and taste, he joked as he licked a slab of snow — is invaluable.

“It’s sort of like a cat-and-mouse game with the snowpack,” he said. “… It’s so spatially variable.”

To accommodate for that spatial variability, forecasters rely on a bank of data and public observations. Even uneducated observers who might not know what they are looking at can submit photographs of the snowpack through the Colorado Avalanche Information Center’s observation portal or mobile application.

Chris Bilbrey, a forecaster with the Colorado Avalanche Information Center, offers a look at the size and shape of snow crystals from a snow pit near Andrews Lake. “It’s sort of like a cat-and-mouse game with the snowpack,” he said of his work.
Reuben Schafir/Durango Herald

Not your typical 9-5

“I’m intimate with about 20 different weather stations,” Bilbrey said.

Five provide high elevation wind and temperature data, while the rest track snowfall, snow-water equivalent and snow temperature. Bilbrey said he can identify data gaps after factoring in observations from the public, other forecasters, weather forecasts and data on recent avalanches into the model.

“Where we have gaps in data is where we target field work,” he said.

Even on his off days, Bilbrey said he consults his 20 weather sources. The weather is constantly affecting the snowpack’s narrative. To take a day off would be akin to skipping a chapter in a book, and then trying to write the subsequent chapter yourself.

At 1 p.m. each day, forecasters across the state meet virtually with the Colorado Avalanche Information Center’s weather head forecaster. The center releases a forecast daily at 4:30 p.m. for the next two days.

The center also began releasing forecasts for the next two days in the afternoon, rather than at 8 a.m. as it had previously done. The change not only made for a more sustainable workload for forecasters, but it provides users who leave in early morning hours with information before their departure.

“It’s real forecasting now, versus now-casting,” Bilbrey said.

At the meeting, forecasters work to parse the data to predict the hazards and risk levels. And, they can expect to have their conclusions challenged.

“There’s no punches saved,” Hodgetts said. “You have to have pretty thick skin.”

The Colorado Avalanche Information Center began a new method of forecasting this season; rather than determining avalanche risk for preset regional zones, the map is now constructed of over 100 polygons that forecasters work to group together according spatial differences in the snowpack. This allows the organization to produce a more accurate forecast that is tailored to a specific region.

“I think it’s a better product,” Hodgetts said.

Chris Bilbrey, a forecaster with the Colorado Avalanche Information Center, digs between 80 and 110 snow pits each year and becomes intimately familiar with the San Juan Mountains’ snowpack.
Reuben Schafir/Durango Herald

After forecasters determine the layout of the map, they use the information they’ve collected to assess the top hazards — meaning the types of avalanches that are likely — and the total risk at the three elevation categories (below, near and above tree line).

This too, is an inexact but thoughtful process. Although forecasters spend much of their time parsing data, writing the so-called narrative is an art in and of itself.

The Colorado Avalanche Information Center website stores a wealth of observations and information that well-educated users can access to assess the conditions. But many don’t, and forecasters try to distill the conditions into a concise message to appeal to the lowest common denominator of users.

“If you have a big storm where we’ll get 20 inches of snow and the wind’s blowing from the southwest, we know its loading northeast facing slopes. To simplify the message, we’ll put storm slab at all elevations (as the biggest hazard) and not talk about the wind loading and instead say ‘avalanches will be bigger and potentially easier to trigger on these aspects,’” Hodgetts said. “… We try to keep it a simple, digestible message.”

After the meeting, which lasts anywhere from 10 to 90 minutes, Bilbrey said he fills out a forecast worksheet in which he “toggles the knobs” until he is satisfied with the product. Forecasters write a summary statement, detailed discussion and record a brief radio announcement each day.

By 5 p.m., the next chapter in the snowpack’s narrative is online, but Bilbrey said forecasters are still active in their group chat, discussing and anticipating the next plot twist.

“We’re all backcountry skiers by heart,” he said. “That’s why we enjoy doing this.”

This story is from DurangoHerald.com.

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