While the calendar says June, the snowpack is still melting from the winter season. Most forecast centers issued their last avalanche advisory at the end of April. So what should you look for if you are planning some high country objectives up above treeline where there is still ample snowpack into the late spring and early summer? BCA has some great advice to share from the Friends of Flathead Avalanche Center. While their tips apply to current northwest Montana conditions, the avalanche hazards they describe could be similar at your mountain destination - so take note!
Above about 6000 feet elevation as of June 1 in northwest Montana, you can find 5 to 8 feet of snow on the ground, with SNOTELs recording 130 to 160 percent of median SWE for the past 47-52 years. In the past week, we've received a half dozen reports of natural and triggered slides, with one person caught.
The take-home message is that avalanche hazards will linger well into summer this year. So whether you are snowmobiling, skiing, hiking, or biking, take a close look at any steep, snow-covered slopes above or around you. Assess your risk from the hazards described below. While the details may seem too long to read, they can keep you and your friends from adding to a long legacy of late-season accidents in the region.
Among them are instances of cyclists nearly caught in slides on the Going-to-the-Sun Road, riders carried in late season slabs, and a hiker killed by debris released by a small wet snow avalanche on the Summer Solstice. Yes, June 21st. Avalanches can pose a hazard until the snowpack is gone.
Loose wet avalanches are the most frequent avalanche problem in the spring and early summer. Unconsolidated new snow or saturated old snow sheds off steep terrain with rising temperatures, sun, or rain. While these slides release from a single point, they can produce a surprisingly powerful amount of debris when they run long distances or entrain a lot of snow. Rollerballs, pinwheels, or natural sluffs warn of decreasing stability. Move to colder snow or lower angled terrain when the snow becomes slushy or gloppy, and use extra caution in and below long, confined gullies.
Spring snowstorms often mean a return to winter-like conditions and a revival of dry snow avalanche problems: wind slab, storm slab, and loose dry avalanches. The danger these pose depends on the amount of new and drifted snow that accumulates, with more snow equaling larger, longer-running avalanches. Their sensitivity to human triggers tends to diminish after several days. During active weather, monitor storm totals, wind loading patterns, and bonding of the new snow to old snow surfaces, particularly melt-freeze crusts. Shooting cracks, more than a foot of new snow, or blowing snow are signs to stay off terrain steeper than 35 degrees.
Wet slab, glide, and cornice fall avalanches can be less frequent yet still destructive late spring and early summer dangers. Wet slab avalanches usually fail during prolonged or intense warmups, as meltwater pools and compromises the strength of deeply-buried weak layers. Your best defense is to travel early while the snowpack is frozen. Post-holing in wet snow is a sign you’re not welcome in avalanche terrain. Meltwater in the snowpack can also lubricate the ground, resulting in unpredictable and catastrophic glide avalanches. Avoid traveling below slopes with glide cracks or large, overhanging cornices, especially during or shortly after warmups. These conditions can result in very destructive debris that runs across all elevation bands onto bare ground.