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With a snowy weekend ahead, Juno’s urban avalanche forecast begins

With a snowy weekend ahead, Juno’s urban avalanche forecast begins
Behrendts avalanche path on Mount Juno, taken from Glacier Avenue on February 27, 2021. (Photo by Jennifer Pemberton / KTOO)

As heavy snow hits Southeast Alaska this weekend, Juno’s Urban Avalanche Forecast will be operational for the first time this season.

Tom Mattis is Juno’s emergency program manager. He says he will keep an eye on the mountains for when the avalanche cycle starts later this week.

“In the backcountry in the high mountains, there are going to be huge avalanches,” he said. โ€œI don’t necessarily see this coming to urban environments just yet. But things are going to change drastically in the next few days.

Mattis says the recent cold snap, combined with the forecast for this weekend, will create ideal conditions for avalanches in the higher mountains.

โ€œWe will see several feet of snow over several days. And during that time, it is warming, and at the end of it will also see some rain at sea level. So it is all going in the wrong direction,โ€ he said .

The incoming snow may not bond well with the existing snowpack, increasing the risk of avalanches.

“We’re going to see an inverted snowpack where we’re going to have heavier, denser snow laying over lighter, looser snow,” he said.

juno face high urban avalanche risk Compared to any American city, there are many more neighborhoods and streets with avalanche paths. mattis update urban avalanche advisory daily at 8 a.m. throughout the season, with a rating on a danger scale that runs from 1 to 5. Updates will go live from this Saturday.

Tom Mattis, Juno’s emergency program manager, is investigating avalanche conditions in Juno’s backcountry. (Photo by Andres Camacho / KTOO)

Forecasting avalanches can be complicated. Mattis monitors snow accumulation throughout the season and closely monitors daily weather forecasts. He also measures the snowpack with repeated field trips to look for weak ice layers.

Many of Mattis’ views have centered on how the layers of ice interact.

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“It starts with what’s on the ground in the mountains,” Mattis said.

This winter, Juneau hasn’t had many days of heavy snow. This means that the rough terrain is still open, with trees, rocks, bushes and shrubs helping to anchor the snow. That will start to change as the snow settles later this week.

“As we start to see more and more snow in the area, those things start to get buried, and the more they’re buried, and the wider areas you have that are smooth and flat, the bigger your starting areas are.” Will go,” Mattis said.

During winter, the risk depends less on the amount of snow and more on the stability of the weather. Even winters with excessive amounts of snow can be relatively safe if that snow continues to fall throughout the season. This tends to form a stable snowpack in the mountains. But weaker layers form when snow storms occur between long intervals of sunshine, wind or rain. This makes the snowpack unstable.

The city only forecasts for urban avalanche risk, but Mattis said that could be a good proxy for people venturing out into the backcountry, or even on the Flume Trail and Upper Perseverance Trail near downtown . When urban avalanche risk is high, backcountry risk will be even more extreme.

Mattis will update his forecasts daily. He encourages people to stay informed as conditions change throughout the winter.

“People have to make their own educated decisions,” he said. “But you go through periods of time that are fairly safe. And then you know overnight, you can have a situation that changes and things become very dangerous.

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Mattis encourages anyone who ventures into the backcountry to submit avalanche observations Alaska Coastal Avalanche Center.

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