Avalanche Forecast

Issued: Jan 31st, 2018 6:06PM

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

shorton, Avalanche Canada

Lizard-Flathead.

Although recent avalanche activity has declined, we've been in a prolonged period of significant avalanche activity. Uncertainty about deeply buried weak layers warrants conservative terrain choices.

Summary

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

THURSDAY: Light flurries with accumulations of roughly 5 cm / moderate west wind / alpine temperatures around -8 C.FRIDAY: Weak frontal system bringing 5-10 cm of snow / moderate west wind / alpine temperatures around -6 C.SATURDAY: Moderate snowfall (amounts highly uncertain at this point) / moderate to strong west winds / alpine temperatures around -4 C.

Avalanche Summary

No new avalanches were reported on Wednesday, suggesting the cooling trend has reduced the likelihood of natural avalanches for the moment.However, large storm slab and deep persistent slab avalanches have been reported on a regular basis for the past few weeks. On Tuesday, numerous large avalanches (size 2-3.5) were triggered naturally as well as with explosives. Many of the natural avalanches were triggered by cornices falling and releasing slabs on the December and November layers, producing 150-250 cm thick crowns. See the avalanche photos in this Mountain Information Network report for an example. The snowpack is still weak and additional stress (such as a cornice or person) could still trigger larger persistent slab avalanches.

Snowpack Summary

The most recent snowfall was accompanied with strong gusty winds, leaving touchy slabs in the alpine and large fragile cornices. Warm temperatures on Monday left moist snow and crusts up to 1700 m.For the past month we have seen regular avalanche activity on multiple weak layers. A layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects was buried mid-January and is now 60-80 cm deep. Another surface hoar layer from early-January is buried 90-110 cm deep. A widespread weak layer from mid-December is composed of facets, crusts, and surface hoar and is now buried 120-160 cm deep. Finally, a rain crust with sugary facets buried late-November is near the bottom of the snowpack and is up to 200-250 cm deep. The bottom line is the snowpack structure in this region is weak. Human triggering is most likely on the shallower weak layers, but any avalanche has the potential to step down to deeper layers and become much larger.

Problems

Storm Slabs

Recent storm snow remains a concern for human triggering, especially on freshly wind-loaded slopes. Furthermore, a small avalanche has potential to step down to deeper layers and become much larger.

Choose low-angle, well supported terrain without convexities.Avoid freshly wind loaded areas.Watch for whumpfing, hollow sounds, and shooting cracks.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

Several deeply buried weak layers are regularly producing large destructive avalanches. Cornices have been a common trigger, so be sure to avoid exposure to overhead hazards.

Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Avoid steep convexities or areas with a thin or variable snowpack.Avoid steep slopes below cornices.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Feb 1st, 2018 2:00PM