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Avalanche Forecast

Archived

Mar 15th, 2020–Mar 16th, 2020

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

Regions

Purcells.

Expect an upward swing in temperatures as the freezing level rises on Monday. This shift in temperature may result in a rise in the likelihood of triggering persistent slab avalanches. Be especially cautious underneath steep sun exposed slopes and around rock outcrops.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SUNDAY NIGHT: Mainly clear, light northeast wind, alpine temperature -8 C.

MONDAY: Clear skies, light northwest wind, alpine temperature -1 C, freezing level 1800 m.

TUESDAY: Mix of sun and cloud, light northwest wind, alpine temperature -2 C, freezing level 1700 m.

WEDNESDAY: Mix of sun and cloud, light northwest wind, alpine temperature -4 C, freezing level 1500 m.

Avalanche Summary

There were reports of a few natural wind slab avalanches on the weekend size 1.5 to 2.5 on north and southeast aspects in the alpine. 

Snowpack Summary

Recent moderate to strong northeast and east wind has redistributed the snow and formed wind slabs at all elevations. New snow from last week may sit on a weak surface hoar layer and a sun crust on steep solar aspects. 

A weak layer of surface hoar buried February 22 may be found 50-100 cm deep. It may sit over a crust on solar aspects. This persistent weak layer will likely remain a problem until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.

Deeply buried facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.