Avalanche Forecast

Issued: Feb 27th, 2017 4:43PM

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

Avalanche Canada cam_c, Avalanche Canada

Conditions are primed for people triggering avalanches, which are expected to get bigger and more touchy with more snow and wind, and warmer temperatures. Deeper persistent slab problems are a real concern in northern parts of the region.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TUESDAY: Mainly cloudy with light flurries in the afternoon bringing trace amounts during the day and 3-8 cm overnight into Wednesday accompanied by strong to extreme southwesterly winds. Freezing level to 500 metres with alpine temperatures around -10 C.WEDNESDAY: Mainly cloudy with scattered flurries bringing around 5 cm of new snow. Strong westerly winds and freezing level to 1000 metres with alpine temperatures around -5 C.THURSDAY: Mainly cloudy with flurries bringing around10-15 cm of new snow. Strong southwesterly winds and freezing level to 1500 metres with alpine temperatures around -5 C.

Avalanche Summary

Reports from the weekend include one observation of a natural wind slab (size unknown, likely 1-2) on a northeast aspect in direct response to wind loading from the southwest, as well as strong northeasterly winds causing multiple natural avalanches up to Size 2 on lee aspects at treeline and above in the Duffey Lake area.Reports from last week and over the weekend include at least three persistent slab avalanches up to 1.5 m deep and Size 3 destructive potential in the Duffy Lake and Hurley Pass areas. The failure planes of each slide remain uncertain, but the early February surface hoar layer was suspected in at least one occurrence and facets in another.While wind slabs remain an ongoing concern throughout the region a low-probability/high consequence avalanche problem should be driving a more cautious approach to backcountry travel, particularly in the northern parts of the region.

Snowpack Summary

10-35 cm of recent snow (with the greatest accumulations in the Cascades) has been blown into touchy wind slabs by southwest an more recent northeasterly winds, which are bonding poorly to facets and buried surface hoar, as well as crust on previously sun-exposed slopes. Reports from the Duffy Lake area on Sunday include easy whumphing and cracking observed at ridge top. The widespread mid-February crust can be found down 20-60cm and seems to be well-bonded, although it has been faceting and weakening recently. In the northern part of the region, a facet/surface hoar weakness buried early February, is now down 60-100 cm and remains reactive in snowpack tests. It is also suspected as the failure plane in at least one of two recent large persistent slab avalanches in the Hurley Pass area. In the Cascades, the mid and lower snowpack are well settled and strong.

Problems

Persistent Slabs

An icon showing Persistent Slabs
A possible pattern of persistent slab avalanche activity has emerged in the northern part of the region. Anyone recreating in the mountains north of Pemberton is urged to choose conservative terrain and exercise extreme caution on northerly aspects.
Avoid steep convexities or areas with a thin or variable snowpack.Be cautious in shallow snowpack areas where triggering is more likely.Be aware of the potential for large avalanches due to the presence of deep weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 4

Wind Slabs

An icon showing Wind Slabs
Watch for wind slabs in the lee of exposed, higher elevation terrain features. Shifting winds mean that slabs can be found on a range of aspects.
Be aware of increased wind slab danger in the south of the region.Be cautious as you transition into wind affected terrain.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Feb 28th, 2017 2:00PM

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