Avalanche
A heat wave has brought summer temperatures to the Rocky Mountains, and the wintry snowpacks are coming unglued. Numerous wet loose avalanches have been reported in the last several days, and as meltwater works its way deeper into the snowpack, the prospect of large wet slab avalanches grows more likely.
On Thursday, Alta, Utah, recorded a high of 61° F at its base area. Arapahoe Basin recorded highs of 51° F at more than 11,000 feet and has not cooled below freezing the past two nights. High pressure and warm temperatures are expected to persist for the next seven days, raising the risk of a wet slab avalanche cycle.
Wet slabs are currently on the problem list at nearly every backcountry avalanche forecast center in the West. Many mountain ranges have been experiencing a persistent weak layer problem that has now been combined with an intense heat wave. Avalanche forecasters are carefully monitoring the flow of liquid water in the snowpack, and in several cases, they have already observed weak layers becoming damp. When the critical amount of liquid arrives at these layers is still up in the air, and that uncertainty is reflected in many of the avalanche forecasts.
“Don’t entirely trust any of these slopes until temperatures dramatically cool down,” the Colorado Avalanche Information Center forecast said. “Each day, the sun climbs higher in the sky, and the oppressive heatwave sends meltwater deeper into colder snowpacks. Wet slabs release when meltwater reaches and pools at these weak layer interfaces. The exact timing is hard to predict, but our best guess is that it’s happening now,” the Sawtooth Avalanche Center forecast said.
The Bridger Teton Avalanche Center received an observation of a wet slab avalanche that appears to have released naturally. To the North, the Big Sky Ski Patrol reported a backcountry avalanche that could have been a wet slab released by rockfall. These smaller-sized avalanches indicate that water is definitely reaching weak layers and carving out slabs, and that larger, far more destructive wet slabs may be possible in the coming days.
With heat expected to persist and meltwater continuing to penetrate deeper into the snowpack, conditions are aligning for a potentially widespread wet slab cycle on the weekend.
