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Avalanche Forecast

Jan 30th, 2018–Jan 31st, 2018
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: South Columbia.

Conditions remain primed for human-triggered avalanches. Give the snowpack time to settle: Simple terrain is recommended for the time being.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday: Scattered flurries (5 cm snow possible). Light westerly winds. Alpine temperature near -8.Thursday: Occasional flurries (5-10cm snow). Light to moderate south-westerly winds. Alpine temperature -7. Friday: 10-20cm of snow. Moderate south west winds. Alpine temperature near -5. More information can be found in the Mountain Weather Forecast.

Avalanche Summary

A widespread natural avalanche cycle to Size 4 was reported on Tuesday, at all elevations and aspects. Large avalanches were running even at low elevations. See here for a good example in a MIN report. Many large avalanches were also running on the mid December persistent weak layer, down approximately 150cm.On Saturday a human-triggered Size 2.5 avalanche was reported near 2300m on a south west aspect in Glacier National Park. See the MIN report for incident details. Conditions will remain primed for human triggered avalanches, with the potential for some surprisingly large avalanches given how many persistent weak layers exist in the snowpack.

Snowpack Summary

60-90 cm of snow fell from Sunday through to Tuesday and temperatures warmed up to -1 at tree line on Monday. Winds were strong to extreme from the south, building cornices and creating wind slabs on lee (down wind) slopes.The new snow sits on a complex snowpack and there are three active weak layers that professionals are monitoring:1) 70-110 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at tree line elevations and possibly higher. 2) Deeper in the snowpack, the early-January persistent weak layer is 100 to 140 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands. 3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 120 to 170 cm deep. It is most problematic at and below tree line.

Avalanche Problems

Storm Slabs

Warming temperatures put heavier snow on top of lighter dry snow - a recipe for an unstable snowpack. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.
The new snow will require several days to settle and stabilize.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Be wary of slopes that did not previously avalanche.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3

Persistent Slabs

Several weak layers are buried in the snowpack, creating very large avalanches when triggered.
Make conservative terrain choices, remembering avalanches may be surprisingly large.Avoid open slopes and convex rolls where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 4