Avalanche Forecast

Issued: Nov 26th, 2018 4:48PM

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

Avalanche Canada dsaly, Avalanche Canada

More snow and increasing winds increase the likelihood for slab avalanches to develop. If snowfall amounts exceed 25 cm, avalanche hazard will be higher than indicated.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain

Weather Forecast

Snow forecasts identify the largest snowfall amounts occurring in the St Mary's drainage area of the Purcells forecast region.MONDAY NIGHT: Cloudy with flurries / Accumulation: up to 10 cm / Alpine temperature: Low -1C / Light southwest ridge wind / Freezing level 1500mTUESDAY: Cloudy with flurries / Accumulation: up to 15 cm / Alpine temperature: High +1C / Light to moderate southwest ridge wind / Freezing level 1500mWEDNESDAY: Cloudy with sunny breaks and flurries / Accumulation: up to 5 cm / Alpine temperature: high 0C / Moderate decreasing to light southwest ridge wind / Freezing level 1600mTHURSDAY: Cloudy with sunny periods / Accumulation: trace / Alpine temperature: High -1C / Light ridge winds

Avalanche Summary

On Saturday, a large human triggered avalanche was reported in the South Columbia forecast region. The size 3 avalanche occurred on a steep, north aspect in the alpine and failed to ground, likely on the October crust. This avalanche is notable for the Purcells where we have a similar, but shallower snowpack than in the South Columbia, resulting in a higher possibility of impacting a weak layer near the ground. Find the MIN report here.Small windslabs have been triggered by skiers and explosives in cross-loaded and lee terrain features at treeline and alpine elevations. Earlier in the month, a natural avalanche cycle took place over the late October crust/facet combination. Be aware of the continued possibility for smaller avalanches to 'step down' or even initiate at this deeper layer.

Snowpack Summary

Snowfall through Monday afternoon has deposited up to 10 cm around the region. This added to recent snow, has buried a surface hoar/sun crust layer down about 10-30 cm. Reports in the region show this variable layer sitting above a layer of recently reactive wind slab. This wind slab layer overlies yet another widespread layer of surface hoar from mid-November, now found about 30-50 cm deep. A final, prominent feature of the snowpack is a combination of a melt-freeze crust and underlying sugary, faceted snow found around the base of the snowpack. Avalanches have been triggered where there is a slab above this crust.

Problems

Storm Slabs

An icon showing Storm Slabs
Up to 10 cm snowfall through the day on Monday has increased the load on this layer now buried about 10-30 deep. Older, stubborn wind slabs may be buried under more recent snowfall.
Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Caution in lee and cross-loaded terrain near ridge crests.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
A nasty combination of crust and sugary, faceted snow exists at the base of the snowpack in the alpine. This weak layer has already produced large avalanches in alpine terrain and ridge top features.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Nov 27th, 2018 2:00PM