Avalanche Forecast

Archived

Feb 6th, 2021–Feb 8th, 2021

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 unlikely, human triggered possible.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Large human triggered avalanches are likely this weekend, particularly on slopes above 1600 m. Conservative terrain choices are critical right now. The persistent weak layer of surface hoar will be slow to gain strength.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Brrrr! Arctic air ushers in bitterly cold temperatures with no new snow in sight.

SATURDAY NIGHT: Overnight low temperature around -30 C, light to moderate north wind, trace of snow possible.

SUNDAY: Clear skies, daytime high temperature around -15 C, light northwest wind, no snow expected.

MONDAY: A few clouds, daytime high temperature around -25 C, light variable wind, no snow expected.

TUESDAY: Clear skies, daytime high temperature around -25 C, light north/northeast wind, no snow expected.

Avalanche Summary

No new avalanche observations to report from Friday.

On Wednesday and Thursday wind slab development was noted in the Kakwa, more details and images here.

On Wednesday there were reports of numerous natural avalanches 20 to 40 cm in depth running at and above treeline. A southwest slope produced a size 3 natural avalanche. These avalanches presumably ran on surface hoar which was producing very touchy conditions. There are some great visuals of this activity in this MIN.

Snowpack Summary

Since Wednesday the north has gotten 16 to 20 cm while the south half of the region has received 25 to 40 cm, with the Renshaw being the big winner.

This means that there is now 40 to 80 cm of snow resting on buried surface hoar which is most prevalent above 1600 m, it likely reaches into the alpine too, we're just not sure how high it extends.

Below 1600 m this snow is resting on a crust.

There are presently no deeper concerns in the snowpack.

Terrain and Travel

Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.