Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Mar 16th, 2020–Mar 18th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Watch for lingering wind slabs in the alpine. New soft slabs formed below treeline on the weekend and overlie a persistent weak layer of surface hoar--this creates the unusual situation where low elevation danger remains a concern while upper elevations gradually improve. 

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Monday Night: Flurries possible but no significant accumulation. Moderate to strong winds changing from westerly to northerly at ridgetop. Light and variable winds below treeline. Temperature falling to -10 or so. Mostly cloudy.

Tuesday: No significant precipitation. Light to moderate wind from the northeast at ridgetop. Light northeast winds below treeline.Temperatures -5 to -15. A few clouds.

Wednesday: No significant precipitation. Light winds from the north and northwest at ridgetop. Calm to light and variable winds below treeline.Temperatures -5 to -10. A few clouds.

Thursday: No significant precipitation. Light and variable winds. Temperatures -5 to -15. A few clouds.

Avalanche Summary

A wind slab avalanche cycle up to size 2.5 was observed on Saturday. One size 3 was reported on a south aspect as well. No avalanches were reported at lower elevations where surface hoar is known to exist but observations are scarce.

Natural avalanches are unlikely in the next few days as a cooling trend occurs. However, human triggering of isolated lingering wind slabs at upper elevations remains a possibility, especially on steep southerly slopes if the sun is strong. At lower elevations, human triggering of avalanches is also possible where slabs, even very soft ones, may now exist over persistent weak surface hoar layers, again perhaps somewhat more likely on sunny slopes.

Snowpack Summary

Temperatures had less of an effect over the weekend than expected but the sun was strong enough to create a new surface crust on steep southerly terrain, probably more so at lower elevations. Winds have continued to transport snow at upper elevations creating new wind slabs in some areas that were unstable on Saturday. At lower elevations, winds have created soft slabs in open areas below treeline. Two surface hoar layers 50-60cm and 75-90cm below the surface remain a concern especially if there's a slab on the surface from warming and/or winds over the weekend. 

A cooling trend will likely tighten the bonds in the snowpack for the next few days. In the alpine, where windslabs are the main issue, this will probably improve some of the instabilities that came up over the weekend. However, at lower elevations more cohesion in the upper snowpack could actually increase the sensitivity of the persistent weak layers of surface hoar. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Approach lee and cross-loaded slopes with caution.
  • Be very cautious in open terrain features, such as cutblocks, gullies, and cutbanks.

Problems

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.

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.