Avalanche Forecast

Issued: Jan 29th, 2018 4:43PM

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

mgrist, Avalanche Canada

South Columbia.

Heavy snowfall and rising temperatures will cause a widespread avalanche cycle. It's best to avoid all avalanche terrain, free from overhead hazard.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Tuesday: 5-15 cm snow Monday overnight into Tuesday, with another 10-15cm during the day. Moderate south-easterly winds. Alpine temperature near -8. Wednesday: Scattered flurries (5 cm snow possible). Moderate south-westerly winds. Alpine temperature near -8.Thursday: Scattered flurries (5-10cm snow). Light to moderate to strong south-westerly winds. Alpine temperature -7. More information can be found in the Mountain Weather Forecast.

Avalanche Summary

A widespread natural storm slab avalanche cycle to Size 3.5 was reported on Monday, at all elevations and aspects. Large avalanches were running even at low elevations. See here for a good example in a MIN report. 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. Expect natural avalanche activity to continue through Tuesday, with the potential for some surprisingly large avalanches given how many persistent weak layers exist in the snowpack.

Snowpack Summary

15-35 cm of storm snow fell Sunday into Monday and temperatures warmed up to -1 at tree line. The snow fell with strong south winds at times, producing wind slabs in lee features at tree line and alpine elevations and in open areas below tree line.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

Heavy snowfall and warming temperatures are a recipe for widespread avalanches. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.If triggered storm/wind slabs may step down to deeper layers and result in very large avalanches.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Persistent Slabs

Several weak layers are buried in the snowpack, creating very large avalanches when triggered.

Avoid open slopes and convex rolls where buried surface hoar may be preserved.Make conservative terrain choices, remembering avalanches may be surprisingly large.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

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