Avalanche Forecast

Archived

Apr 27th, 2014–Apr 28th, 2014

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Northwest Inland.

We are no longer issuing danger ratings for this region due to a lack of field data.Please refer to this blog post for more insight into managing the current conditions.

Weather Forecast

Synopsis: The weather should remain cool and unsettled with winter conditions at higher elevations through Monday. Expect light to moderate precipitation combined with increasing Southwest winds. A ridge of high pressure is forecast to build over the South and Central regions early next week. The ridge should bring warm temperatures and rapidly rising freezing levels, but may not be strong enough in the North to deflect Pacific moisture or clear the cloud from the skies.

Avalanche Summary

Expect new wind slabs and thin storm slabs to develop above recent melt-freeze crusts. These slabs may be easily triggered due to the hard sliding layer of the melt-freeze crust. Daily melt-freeze cycles may be weakening cornices, and they may fall off naturally or be easily triggered. Rain at lower elevations may cause new snow to weaken rapidly and slide out of steep terrain, sometimes gathering mass in constrained terrain features. Deep persistent weak layers may be triggered by rapidly warming temperatures, strong solar radiation, or rain.

Snowpack Summary

The spring snow-pack is comprised of many layers of melt-freeze crusts, thin new snow layers, and stiff wind slabs in the alpine. The snow-pack may be very different depending on elevation, with moist or wet snow in the valleys and near winter conditions in the alpine. The weather can change rapidly at this time of year, and this may result in different types of avalanche problems. Danger is most likely to increase if there is a substantial new snow storm with wind, or if the temperatures increase rapidly with or without sunshine. Our plan is to place a link in the headline that explains general risk scenarios associated with the forecast weather. We will not issue danger ratings for this region due to the lack of data as a result of professional operators closing for the season.

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.