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Avalanche Forecast

Archived

Mar 28th, 2020–Mar 30th, 2020

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

Regions

Northwest Coastal.

This forecast lacks field observations and has lots of uncertainty. This will be the last avalanche forecast of the season. Reactive storm slabs remain the primary concern, especially around ridge features and wind loaded terrain.

Confidence

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

Weather Forecast

Saturday night: Flurries and snow, 5-10 cm. Alpine low temperature -7 C.Moderate south-southwest wind.

Sunday: Flurries and snow, 5-15 cm. Alpine high temperature -4 C. Moderate south wind.

Monday: Cloudy with scattered flurries, up to 10 cm. Alpine high temperature -10 C. Light to moderate east wind.

Tuesday: Mostly cloudy. Alpine high temperature -10 C. Light east wind.

Avalanche Summary

A large (size 2.5) natural glide slab release was observed on Tuesday. The debris from the release overran the John Little Falls hiking trail. Natural glide slab activity has been a regular occurrence during recent periods of daytime warming, reinforcing the importance of avoiding glide cracks and areas exposed glide slab hazards.

There are very limited field observations at this time and no recent avalanches have been reported.

Snowpack Summary

Upwards of 10-30 cm of snow has accumulated around the region over the past few days, along with a steady westerly wind. This covers a variety of wind-affected surfaces and a melt freeze crust on south aspects and slopes below 1100 m.

A layer of surface hoar crystals is buried around 30-60 cm in sheltered areas at and below treeline, shallow enough for human triggering on steep slopes where it is preserved. Recent observations of this layer are lacking.

An early-season layer of faceted grains and a melt-freeze crust can likely be found near the base of the snowpack at high elevations. A large load, such as a large cornice fall, may have potential to trigger it.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.