Avalanche Forecast

Archived

Apr 12th, 2023–Apr 13th, 2023

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 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

Glacier.

Reactive storm slabs are propagating widely over a crust on solar aspects at treeline and alpine elevations, minimize your exposure where the sun is warming the snow surface.

Below treeline loose wet avalanches are easily triggered and gain mass quickly as the run on a widespread crust.

Confidence

Moderate

Avalanche Summary

Multiple solar triggered storm slab and loose wet avalanches up to size 3 were observed along the hwy corridor and in the backcountry on Wednesday. These avalanches showed wide propagation failing at the Mar 31 layer and running far into the runout zones. A field team was also able to easily trigger multiple small avalanches in the moist surface snow also failing on a widespread crust below tree line.

Snowpack Summary

35cm of storm snow and strong, gusty SW winds have formed a reactive storm slab, thicker in lee features. This slab is propagating and stepping down to the March 31 layer (crust on solar aspects, facet/surface hoar on polar aspects).

The snowpack is generally strong. However, the Nov 17 basal weakness can still be found near the ground in many locations.

Weather Summary

Calm weather prevails for the remainder of this week with gradually rising freezing levels and some isolated flurries.

Thurs: Mix of sun & cloud, Alp high -5*C, light W winds, 1600m FZL

Fri: Mix of sun & cloud, Alp high -5*C, light SW winds, 1700m

Sat: Cloudy w/ sunny breaks, flurries, Alp High -2*C, light SW winds, FZL 2000m

Terrain and Travel Advice

Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

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.

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.