Avalanche Forecast

Issued: Jan 5th, 2018 5:36PM

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

mgrist, Avalanche Canada

South Rockies.

Expect persistent slab avalanche activity to continue as the snow sitting above the persistent weak layer further settles and consolidates. Adopt a conservative approach in the coming days.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Occasional flurries with minor accumulations through the forecast period.SATURDAY: 2-5cm Friday overnight into Saturday, with another 2-5cm possible throughout the day / Strong to moderate southwest wind / Alpine temperature -4 / Freezing level 900mSUNDAY: Cloudy with flurries / Moderate west wind / Alpine temperature -4 MONDAY: Cloudy with isolated flurries, accumulation 3-10cm possible / Light southwest wind / Alpine temperature -3

Avalanche Summary

Continued avalanche activity was observed in steep low elevation terrain (road cut banks) in the Elk Valley on Wednesday to size 1.5. These were triggering very easily. See here for details in the MIN. On Monday, a machine triggered Size 1.5 persistent slab avalanche was reported running on the mid December surface hoar layer, down 35 cm at that location (1700m). See the details here in a Mountain Information Network (MIN) post. Expect to see persistent avalanche activity continue as temperatures revert to a normal regime (warmer in the valleys and colder with elevation) and snow sitting above persistent weak layers settles more rapidly.

Snowpack Summary

Up to 45 cm of snow fell to end 2017. Since then, temperatures have warmed up from the deep freeze and moderate to strong winds (primarily from the south west) have redistributed that snow into wind slabs at tree line and above. Some windward slopes have been scoured to ground. The main concern in the snowpack is a weak layer buried mid-December, which consists of a crust on solar aspects and feathery surface hoar in sheltered terrain at and below tree line. This layer has consistently shown to be reactive to human triggers. The lower snowpack is composed of mostly soft sugary faceted snow and early season crusts. Avalanche hazard for tree line elevations and below may be one step lower in areas east of the divide.See here for a recent forecaster blog for a summary of the tricky conditions in the snowpack and strategies on how to work around a persistent slab problem.

Problems

Persistent Slabs

A weak layer composed of surface hoar and/or crusts is buried 35-70 cm below the surface. This layer continues to be very reactive to human triggers and may not improve anytime soon.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Choose supported terrain without convexities at treeline where buried surface hoar may be preservedWatch for signs of instability such as whumpfing, or cracking.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Wind Slabs

Moderate winds have created fresh wind slabs at higher elevations. In the south of the region, the winds were from the south-west. In the north of the region the winds were from the north east.

If triggered, the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Jan 6th, 2018 2:00PM