Avalanche Forecast

Archived

Jan 30th, 2018–Jan 31st, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

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.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.