Incoming snow raises avalanche danger
Ryan Summerlin January 16, 2012
Colorado Avalanche Information Center forecasters issued a special advisory for Colorado’s southwest and central mountains Sunday that warns of increased avalanche danger coming with the storm that was expected to push through Colorado at the tail end of the weekend.
Avalanche danger in the area is expected to raise from its current “considerable” rating on most aspects as soon as today, according to forecasts from the CAIC.
Last week, danger hovered around “moderate” to “considerable” on areas at and above tree line, with “low” danger below tree line on less-affected aspects. The danger was the likelihood of triggering small slides in weak snow that’s been wind-loaded.
The CAIC announcement encompasses Steamboat and Flat Tops through the Sawatch Range and Aspen to Grand Mesa and the San Juans, including Vail and Summit County.
In areas where the storm drops more than six inches of snow will be most affected, according to CAIC forecaster John Snook.
“Backcountry users will need to stay focused on rapidly changing snowpack conditions,” he wrote in his report. “Collapsing snow, cracking and recent slide activity are all signs of instability telling you to stay well away from terrain steeper than 30 degrees.
“Do not allow powder fever to steer you toward poor travel decisions in avalanche terrain.”
Up to a foot of snow is expected in Gunnison and the southern San Juans, which are favored by storms with southwest flow, with lesser amounts moving north through the western Sawatch Range, Eagle County and Steamboat Springs. Eastern zones, like Summit County, are expected to receive even less snow.
The storm is quick and powerful, with brevity that could limit total accumulations. But the brief period of moderate snow combined with moderate winds could add a quick load to the already weak snowpack.
Forecasters also expect temperatures to drop today, which will combine with the recently fallen snow and winds to generate brittle wind slabs.
Brisk alpine winds earlier this week affected snowpack with drifts and by creating wind slabs on aspects facing north through east to south. Several slides in the Vail Pass area stepped down into older snow layers on Thursday, marking the tenderness of the snowpack layers.
It’s all very weak, Snook says, with new wind slabs resting on persistent hard slabs.
Avalanche mitigation along Loveland Pass on Thursday triggered several medium sized hard slab avalanches in highly wind-affected areas that serve as a reminder of the week’s avalanche discussions.
“These stubborn slabs are hard to trigger, but a large avalanche is possible if you find a weak spot near the slab margin,” Snook wrote in his daily report. “Triggering a small avalanche in the recent wind slabs may also step down and release a larger persistent slab.”
He added that below treeline, triggering slides in the weak, sugary snow is still possible on shady, wind-protected aspects.