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Avalanche Forecast

Archived

Mar 15th, 2021–Mar 16th, 2021

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

Regions

North Rockies.

Spring-like conditions will persist through the forecast period. Natural avalanche activity will likely spike in the afternoon when warming and solar radiation destabilizes the snowpack. 

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

A spring-like diurnal weather pattern is expected through the forecast period. This will bring rising freezing levels to 2000 m by the afternoon then falling back to the valley bottom overnight. No new snow is expected and mostly sunny skies will prevail.

Avalanche Summary

The warm weekend proved to show a widespread natural avalanche cycle primarily loose wet up to size 2 but natural cornice failures were reported as well as some wet slabs seen up to size 2 and potentially larger. Check out these excellent MIN reports from Saturday. 

Upper Burnt MIN Report.

Beaver Creek.

Bullmoose.

With warming and solar input continued, it might lead to deeper releases on the persistent weak layer this week.

Our field team found some large and disturbingly wide avalanches in the Hasler last Tuesday, with lots of compelling images in their MIN report here. It's suspected that these are running on facets that are about 80 cm below the surface.

This adds to the tally of recent large avalanches they started collecting in Pine Pass on Monday. 

Snowpack Summary

The northern portion of the region around the Pine Pass has picked up 35 new cm as of Saturday afternoon but very little new precipitation has fallen in the southern 2/3 of the region. This snow is expected to be redistributed by the strong southwest wind and also felt the heat of the rising freezing levels over the weekend.

Sun crust exists on solar aspects and a temperature crust may exist on all aspects to 1800 m. Wind effect is widespread in the alpine and treeline across the region.

About a metre of snow covers a weak layer of facets buried mid-February. Slightly deeper there is a widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.

Terrain and Travel

  • Avoid avalanche terrain during periods of strong sun.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.