Avalanche danger high after snowfall

Jon Jeresek knows all too well the beauty of the backcountry can become dangerous in an instant.

As the Flathead Avalanche Center forecaster, Jeresek has seen firsthand the accumulated dangers a season of snow can have, especially in fluctuating temperatures.

“There are two things that affect our snow pack, and that is gravity and temperature,” Jeresek said. “And with that, if we get some warming weather, we can get some solidification of our snow pack. It’s been so cold, those cold days in February, that hasn’t happened.”

And that lack of solidification is reason for concern, said Jeresek who has been an avalanche specialist for 27 years.

Jeresek explained early season snowfall became encrusted with warmer temperatures. Subsequent snow with much colder temperatures accumulates on top of the encrusted sheets, and that can become dangerous, Jeresek said.  

A Libby man died in an avalanche on Feb. 22. In that circumstance, the avalanche that befell four Libby men was the perfect storm of late-winter powdery snow atop an encrusted sheet, awaiting the moment to break loose.

The avalanche came crashing down on two of the four snowmobilers as fast as 80 mph, killing Bryan Harlow and covering all of Todd Byington but his face.

Sheriff Roby Bowe said the

Feb. 22 avalanche was human-caused, just enough of a human element occurred to trigger the slide.

“This is the most number of (avalanche) incidents — six — in all my years of doing this,” Jeresek said. “That’s going back to 1987. Our normal is about three.”

Jeresek said he is counting the days until the temperatures climb that will allow for some consolidation of the snow pack, and thus lessen the dangers.

“As soon as we get some warming of the temperatures we’ll get some consolidation of the snow pack, and we get some strengthening. If it settles too fast, and we get some free water in the snow pack, that’s not good, either. But if we get some slow warming and not the free water through, usually we end up with a stronger snow pack.”

Jeresek said elevated temperatures are inevitable and with them will be safer conditions for backcountry enthusiasts.

“I’m hopeful that we’ll see some improvement maybe by the end of (this) week,” Jeresek said. “If not, sometime next week. Normally, we don’t have a period of high advisory as we’ve had this year. We’re into the ninth day of our high advisory, which is unusual for us,” Jeresek said last week. “Usually, we have a high advisory for three days, and then we’ll have some event that will take us back to considerable or moderate. This year is unusual. Very unusual.”

Jeresek said analyzing the snow pack this year has established a series of benchmarks that can track the elevated avalanche season.

“Our Nov. 19 rain-on-snow event created a really thick rain crust on the bottom third of the (current) snowpack. Our next benchmark is the Jan. 11 wind event that actually produced Palouse dust in our snow pack. If you dig down into the wind-blown snow, there it is. It’s dust that was transported with the snow that was with it. The other benchmark for us is the first week of February when we had the double-digit below-zero temperatures, and what that did was change our snow pack at the bottom. It’s working its changes up in the snow pack. It’s working a depth-hoar up in the snow pack. That’s a process that is driven by temperature. It changes and tries to pull water vapor up from the ground. It’s builds crystals below and can form a hard layer, like that Nov. 19 rain event. Yes, it makes the whole snow pack more prone to avalanche. Absolutely. Oh, absolutely. It’s pretty much a guarantee that we will see the impact of that weeklong period in February when it was just bitterly cold.”

The next benchmark has been the recent nine to 11 days of accumulated snowfall, which he called snow-loading.

“This year, we’ve gotten an inordinate amount of wind events, too,” Jeresek said. “And that has an effect on the snow-loading.”

Jeresek said he measures avalanche season by two factors: the number of incident  reports and the other is the number of days under a high advisory.

“This year we’ve seen an exceptionally high number of high-advisory days,” Jeresek said. “Normally, we may see six days a season, and we had nine consecutive days of a high advisory. Most of our season has been at high or considerable.”

Jeresek said the worst may be yet to come.

“I will typically do two incidents a year, and we’ll get more in March and April,” Jeresek said. “Some people are waiting to get out. Typically, we get more people out as temperatures warm up, and that’s when our incidents go up.”

 As hikers get the urge for a cure to cabin fever, Jeresek advised trip planning.

 “They should prepare for their outing to be out during the freezing part of the day,” Jeresek said. “Snow pack is largely safe to be on during the freezing part of the day. Go out and have your fun until 1 or 2 p.m. We can manage risk quite well with our melt and freeze cycles. People should know this: If they’re out in the day until 1 or 2 o’clock, that’s OK. When that time comes they need to get out, quick like bunnies as the melt period begins.”

For more information on the Flathead Avalanche Center, go to www.flatheadavalanche.org.