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Avalanche Forecast

Archived

Apr 12th, 2017–Apr 15th, 2017

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.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Waterton Lakes.

Keep an eye on Thursday's weather - forecast freezing levels and precipitation vary between forecasts. Avalanche danger will depend on new snow amounts. Watch for temporarily elevated danger if rain falls on fresh snow in the lower Alpine.

Weather Forecast

Thursday:  Rain (snow at Alpine elevations), 10-15mm forecast. Ridge wind: Moderate Southerly. Freezing Level 2200- 2500m. Treeline low 0.5, High 2.Friday: A mix of sun and cloud, the odd flurry. Ridge wind Strong SW. Freezing Level 1700m.  Treeline Low -6, High -4.Saturday: Mostly cloudy, isolated flurries possible. Ridge wind: Moderate SW.

Snowpack Summary

A generally well settled spring snowpack, with thick supportive crusts at/near the surface. Rain at/below Treeline may soften these crusts. New snow in the Alpine will be redistributed by wind, building slabs on lee slopes.Well preserved, loose facets make up the lower snowpack in isolated Alpine areas. These have been unreactive for several weeks.

Avalanche Summary

On Tuesday, forecasters observed several small (Size 1) Loose Dry avalanches on NE - SE aspects, in extreme (unskiable) Alpine terrain. These happened as strong April sun hit cold new snow for the first time.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Thursday

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.