Avalanche Forecast

Issued: Jan 29th, 2018 4:32PM

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

mbender, Avalanche Canada

Lizard-Flathead.

Forecast freezing levels and precipitation amounts are uncertain Monday night through Tuesday. If precipitation falls as snow and is at the upper end of estimates, then avalanche danger will remain at HIGH in the alpine.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

TUESDAY: Flurries, accumulations 10-20cm Monday night into Tuesday and another 5-10cm though the day / Moderate to strong southwest wind / Alpine temperature -2 / Freezing level 1000mWEDNESDAY: Isolated flurries / Light to moderate southwest wind / Alpine temperature -7THURSDAY: Isolated flurries / Light to moderate south wind / Alpine temperature -6

Avalanche Summary

On Monday numerous natural and explosives controlled storm snow avalanches were reported to 2 and 2.5 on all aspects in the alpine and tree line. There was also a natural cornice triggered size 3 storm slab avalanche on a north east aspect in the alpine.Several large and very large avalanches have occurred on weak layers buried deep in the snowpack in the last week (including natural activity up to Size 3), highlighting that dangerous avalanche conditions exist within the region. Explosive control work last Friday and Saturday produced numerous storm slab avalanches Size 2-2.5, as well as several large, destructive Size 3-4, slab avalanches that failed on the mid-December and late-November layers, with crowns from 150-250 cm deep.

Snowpack Summary

There is possibly moist snow or a crust on the snow surface up to 1700m as a result of a high freezing level on Monday through Monday night. About 60-100cm of settled storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects, that was buried mid-January. Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets buried late-November is near the bottom of the snowpack and is now up to 200-250 cm below the surface. All of these layers remain active and have produced recent large, destructive avalanches.

Problems

Storm Slabs

New snow and has formed storm slabs, while winds are building cornice and loading lee slopes near ridge top. These slabs have shown the potential for wide propagations running long distances.

Choose low-angle, well supported terrain without convexities.If triggered, storm slabs may step down to deeper layers and result in large avalanches.Avoid freshly wind loaded areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Persistent Slabs

Several weak layers of concern are buried within the snowpack and produced several recent large and very large avalanches. Simple terrain with low angled, supported slopes is a good choice.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Watch for signs of instability such as whumpfing, or shooting cracks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 30th, 2018 2:00PM