Archived

Avalanche Forecast

Feb 14th, 2018–Feb 15th, 2018

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

4: High

The avalanche danger rating at treeline will be high

Below Treeline

4: High

The avalanche danger rating below treeline will be high

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 or cross-loaded slopes.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Cloudy, flurries. Accumulation trace. Ridge wind light to moderate northeast. Temperature -20. Freezing level valley bottom.THURSDAY: Mix of sun and cloud. Ridge wind strong west. Temperature -15. Freezing level valley bottom.FRIDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind moderate, northwest. Temperature -12. Freezing level valley bottom.SATURDAY: Snow. Accumulation 10-15 cm. Ridge wind moderate to strong, northeast. Temperature -20. Freezing level valley bottom.

Avalanche Summary

On 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 Thursday afternoon and overnight into Friday. Several storm slabs and deep persistent slabs to size 4 were reported when visibility improved on Friday. See this MIN post for more information. These avalanches are failing on weak layers deep in the snowpack and running to valley bottoms. See this video for more details.

Snowpack Summary

About 10-15 cm on new snow and strong to extreme winds have resulted in extensive scouring on windward slopes (generally north and west facing slopes) and the creation of wind slabs on down wind (lee) features higher up, on a wide range of aspects. 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 while avoiding all overhead hazard.

Avalanche Problems

Wind Slabs

Strong to extreme 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.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use extra caution as you transition into wind affected terrain.

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.

Be aware of the potential for large, deep avalanches.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Avoid steep convexities or areas with a thin or variable snowpack.

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3.5