Archived

Avalanche Forecast

Feb 15th, 2018–Feb 16th, 2018

Alpine

3: Considerable

Treeline

3: Considerable

Below Treeline

2: Moderate

Alpine

3: Considerable

Treeline

3: Considerable

Below Treeline

2: Moderate

Alpine

4: High

Treeline

4: High

Below Treeline

3: Considerable

Regions: South Rockies.

Wind slabs, cornices and deeply buried weak layers are making for tricky conditions. The best approach is to choose conservative terrain, minimize your exposure to overhead hazards and avoid wind-loaded slopes.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

TONIGHT: Cloudy with clear periods, light flurries. Accumulation trace. Ridge wind strong, west. Temperature -13. Freezing level valley bottom.FRIDAY: Cloudy with sunny periods, light flurries. Accumulation trace. Ridge wind moderate to strong, west. Temperature -9. Freezing level valley bottom.SATURDAY: Snow. Accumulation 10-20 cm. Ridge wind strong, northeast. Temperature -11. Freezing level valley bottom.SUNDAY: Mainly cloudy, light flurries. Accumulation trace. Ridge wind moderate to strong, northeast. Temperature -22. Freezing level valley bottom.

Avalanche Summary

On Thursday both natural and skier triggered wind slabs up to size 1.5 were reported as well as loose, storm snow releases from steep rocky terrain.Tuesday we received reports of size 3 avalanches that were likely triggered by cornice fall over the weekend and ran full path to valley bottom. See here for the MIN report. A widespread natural avalanche cycle occurred late last week with several storm slabs and deep persistent slabs to size 4 reported. See this MIN post for more information. These avalanches were failing on weak layers deep in the snowpack and running to valley bottoms. See this video for more details.

Snowpack Summary

About 20-30 cm on new snow and winds have led to the creation of wind slabs on leeward features at upper elevations on a wide range of aspects. In sheltered areas near treeline and below, these slabs overly a layer of surface hoar buried mid-February that has produced very easy, sudden results in recent snowpack tests.The lower snowpack in this region is weak, with two main concerns: A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 100-150 cm deep. Second, a rain crust with sugary facets buried in late-November is near the bottom of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.The take home message is that weak layers are still active and deserve a lot of respect. The solution is to stick to conservative terrain and avoid overhead hazard.

Avalanche Problems

Wind Slabs

Winds have formed touchy slabs, especially at higher elevations and in wind-exposed terrain. Wind slabs may step down and trigger deep persistent weak layers, resulting in large destructive avalanches.

Use extra caution as you transition into wind affected terrain.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2.5

Deep Persistent Slabs

Several deeply buried weak layers have the potential to produce large avalanches reaching run out zones. Cornices have been a recent trigger for very large avalanches. Avoid shallow rocky snowpack areas where human triggering may also be possible.

Avoid steep convexities or areas with a thin or variable snowpack.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 4

Cornices

Cornices have triggered very large avalanches recently. Be especially wary of long runout distances in avalanche paths, and the possibility of mature timber being taken out by a surprisingly large avalanche.

Avoid steep slopes below cornices.Give cornices a wide berth when traveling on or below ridges.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3.5