Avalanche Forecast

Issued: Mar 4th, 2021 4:00PM

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

Avalanche Canada shorton, Avalanche Canada

Email

Cool cloudy weather has likely reduced the avalanche danger, but heightened conditions still exist on steep and wind loaded terrain.

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Cloudy, windy, and some light snowfall on the way.

THURSDAY NIGHT: Cloudy, moderate southwest wind, freezing level drops to 1200 m.

FRIDAY: Cloudy with some isolated flurries, strong south wind, freezing level climbs to 1800 m with treeline temperatures around -1 C.

SATURDAY: 5-10 cm of new snow by the morning then some sunny breaks in the afternoon, light southwest wind, freezing level climbs to 1300 m with treeline temperatures around -4 C.

SUNDAY: Cloudy with some isolated flurries, light south wind, freezing level around 1200 m with treeline temperatures near -5 C.

Avalanche Summary

Preliminary reports suggest warm weather on Thursday resulted in many small wet loose avalanches on steep south-facing terrain. On Wednesday, in addition to wet loose avalanches, there were a few human triggered slab avalanches showing the impacts of warming on slab avalanche conditions. Two notable incidents were on south-facing slopes in Glacier National Park, including a size 3 wind slab avalanche in a steep alpine couloir (MIN report) and a size 1.5 slab avalanche in below treeline terrain (MIN report).

Persistent slab avalanche activity has dramatically declined in the past week, with the last reports on Feb 24 (two size 3 explosive triggered avalanches on the late January weak layer) and Feb 26 (a size 2 human triggered avalanche in a cutblock on the February facet layer). At this point we are uncertain whether the recent warming has irritated the lingering persistent weak layers or whether they have gone dormant.

Snowpack Summary

Cool cloudy weather will likely form a surface crust on slopes that warmed up on Thursday, most likely all aspects below 2000 m as well as south-facing slopes at higher elevations. Lower elevations will likely have moist surfaces and high shaded terrain will have a mix of soft and hard wind slabs. The lower snowpack has been strengthening with reactivity on persistent weak layers on the decline. The two layers of concern have been a layer of facets that was buried in mid-February (60-100 cm deep) and a layer of surface hoar and/or crusts that was buried in late January (80-120 cm deep).

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.

Problems

Wind Slabs

An icon showing Wind Slabs

Wind slabs may remain reactive in steep open terrain at alpine and treeline elevations, especially on north and east aspects.

Aspects: North, North East, East, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

Warming temperatures may have temporarily increased the likelihood of large persistent slab avalanches. There are two potential layers of concern buried 60-120 cm deep across the region that have produced some sporadic activity over the past weeks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely

Expected Size

2.5 - 3

Valid until: Mar 5th, 2021 4:00PM