Avalanche Forecast

Archived

Feb 4th, 2021–Feb 5th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Rockies.

Strong winds from the northwest will likely redistribute recent storm snow to leeward slopes building reactive wind slabs. Natural avalanche activity may taper on Friday but skier and rider triggering is likely.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Forecast snowfall amounts are uncertain.

Weather Forecast

Friday: A mix of sun, cloud, and flurries accompanied by a strong northwest wind. Alpine temperatures near -10 and freezing levels in the valley bottom.

Saturday: Snow 5-10 cm. Moderate westerly wind. Alpine temperatures low at -23 and a high of -10.

Sunday: Snow 5-10 cm. Ridgetop wind switching to the East and blowing in the light values. Alpine temperatures low of -30 and high of -20.

Avalanche Summary

No recent reports on Thursday. On Wednesday, numerous loose-dry natural avalanches were reported up to size 1.

With forecast strong wind, fresh wind slabs, and recent storm slabs will likely remain reactive Friday. Loose-dry avalanches may occur from steep terrain features.

Snowpack Summary

Up to 35 cm of new snow fell by Thursday morning. The new snow accompanied by a strong west-northwest wind will likely redistribute some of this snow to leeward slopes and terrain features building fresh storm and wind slabs. A surface crust may exist at lower elevations. This additional snow brings up to 60 cm of storm snow (over the past week) that sits above a plethora of old snow surfaces. In the alpine and at treeline the buried surfaces consist of stiff wind affected snow, surface facets, sastrugi, pockets of soft snow, surface hoar in isolated areas sheltered by the wind, and a sun crust on steep solar aspects. Below 1900 m a thick crust can be found underneath the recent snow.

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack (80-150 cm deep). Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be carefully assessed and approached with caution.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
Avoid terrain traps where the consequence of any avalanche could be serious.
Be carefull with sluffing in steep terrain, especially above cliffs and terrain traps.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.