Avalanche Forecast

Issued: Jan 6th, 2018 6:28PM

The alpine rating is moderate, the treeline rating is considerable, and the below treeline rating is moderate. 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. Wind slabs in the alpine and near tree line are a significant concern too.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

Occasional flurries with minor accumulations through the forecast period.SUNDAY: Cloudy with flurries / Moderate to strong west wind / Alpine temperature -4 MONDAY: Cloudy with isolated flurries, accumulation 3-5cm possible / Light southwest wind / Alpine temperature -2 TUESDAY: Flurries becoming snow overnight (5 - 10 cm possible) / Moderate southwest wind / Alpine temperature -4

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

Strong to extreme south west winds picked up on Friday and redistributed snow into wind slabs on north through east aspects, as far down as tree line elevations. Some windward slopes have been scoured to ground. Temperatures have also warmed up significantly from the deep freeze, causing the storm snow from late December to settle and take on more slab-like properties at lower elevationsThe 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 proven to be reactive to human triggers. The lower snowpack is composed of mostly soft sugary faceted snow and early season crusts. Avalanche hazard is likely one step lower in areas east of the divide due to shallower snowpacks and the mid-December layer being less prominent.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 reactive to human triggers and may not improve anytime soon.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Wind Slabs

Strong south west winds have created fresh wind slabs at higher elevations.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 7th, 2018 2:00PM