Avalanche Forecast

Issued: Feb 17th, 2018 4:46PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs, Cornices and Deep Persistent Slabs.

jmcbride, Avalanche Canada

South Rockies.

Intense snowfall beginning late Saturday afternoon and overnight, will increase avalanche danger on Sunday. Conservative terrain with no overhead hazard is a good choice.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Snow. Accumulation 10-20 cm. Ridge wind moderate to strong, east. Temperature -16. Freezing level valley bottom.SUNDAY: Cloudy, light flurries. Accumulation trace. Ridge wind moderate to strong, northeast. Temperature -20. Freezing level valley bottom.MONDAY: Mix of sun and cloud. Ridge wind light, northeast. Temperature -15. Freezing level valley bottom.TUESDAY: Mix of sun and cloud. Ridge wind light, southwest. Temperature -12. Freezing level valley bottom.

Avalanche Summary

Friday, ski cuts and explosive control produced loose storm snow avalanches up to size 1.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 last weekend and ran full path to valley bottom. See here for the MIN report. Avalanche activity will increase as a result of Saturday's storm event. Expect widespread storm slab activity and new cornice growth with intense snowfall and wind-loading. Rapid loading also has the potential to wake up buried weak layers. Conservative terrain with no overhead hazard is recommended.

Snowpack Summary

About 20-40 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 that is 100-150 cm deep, and second, a rain crust with sugary facets buried in late-November near the bottom of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.

Problems

Storm Slabs

New snow and wind will form touchy slabs, especially at higher elevations and in wind-exposed terrain. A slab release near the surface may step down and trigger deep persistent weak layers, resulting in large destructive avalanches.

Avoid avalanche terrain during periods of heavy loading from new snow and wind.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2.5

Cornices

Cornices have triggered very large avalanches recently. Avoid lingering in runout zones below large corniced slopes, and stay well back from corniced ridge lines if traveling above them.

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

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

Valid until: Feb 18th, 2018 2:00PM