Avalanche Forecast

Wind slabs formed Thursday night in the Hurricane Ridge area near and above treeline on north through east aspects. You may still be able to trigger a wind slab avalanche in specific areas on Sunday. Cold temperatures will slow the healing process for this avalanche problem. 

Approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and any slope less than 35 degrees. 

In non-wind affected terrain, loose dry avalanches will continue to be the most identifiable and easiest to manage avalanche problem. Think about sluff management on very steep slopes and what would happen if a small but fast moving loose dry avalanche pushed you into or over a terrain trap.  

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.

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Uncertainty is high regarding how sensitive weak layers remain in the Hurricane Ridge area. Field observations suggest the deeper 2/8 persistent weak layer has become unreactive, but a newer buried surface hoar layer (2/19) may have taken it's place.

With high uncertainty regarding avalanche problems with serious consequences, it’s a good idea to maintain a wide margin for error. Choose supported slopes less than 35 degrees and if you choose to engage in avalanche terrain, identify zones of safety. If you encounter collapses or hear whumpfs in flat terrain, these are clear signs to avoid nearby steep terrain.  

Release of a cohesive layer of soft to hard 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 Slabs.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.

This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.