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Avalanche Forecast

Archived

Apr 20th, 2014–Apr 21st, 2014

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Avalanche danger can rise quickly with afternoon warming and solar radiation. Be aware of changing conditions and overhead hazards.For more insight into spring danger ratings, check out this blog post.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Some areas of the region may receive light precipitation on Monday while other parts may stay dry. A short period of moderate precipitation is expected late-Monday or early Tuesday. Dry, sunny conditions are expected for Wednesday. Monday: Precipitation 0-3mm, freezing level am: 1000m pm: 1500m, ridgetop wind: moderate S decreasing through the dayMon. Night: Precipitation 6-10mm, ridgetop wind: light variableTuesday: Light precipitation 1-4mm, freezing level am: 800m pm: 1500m, ridgetop wind: light variableWednesday: Mostly sunny, convective flurries possible, freezing level am: 700m pm: 1600m, ridgetop wind: light variable

Avalanche Summary

Reports from the north end of the region on Friday include sluffing from steep sun exposed slopes and isolated slab releases from leeward features on ridge crests. We are no longer receiving professional daily reports for the region so public observations are really appreciated right now. If you are out in the mountains, send your observations to [email protected]

Snowpack Summary

Highly variable spring conditions are expected in the region. At lower below-treeline elevations the snowpack is typically wet and isothermal. It has not been refreezing overnight and is melting quickly. Between roughly 1000 and 1500m, the snowpack is undergoing daily melt-freeze cycles. The same conditions can be expected on sun-exposed slopes all the way to mountain-top. On higher elevation north-facing slopes, dry snow can be found. Recent strong S through W winds have scoured windward slopes and created wind slabs in leeward slopes. The early February crust/facet layer is typically down 1.5m or more. A smaller avalanche or a cornice fall may still have the potential to step down to this layer causing very large, destructive 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.

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.