Avalanche Forecast

Expect warm air temperatures and sunny skies to allow wet avalanche conditions to quickly develop Sunday. New rollerballs, fresh fan-shaped avalanche debris, and wet surface snow deeper than your ankle all indicate that you may be able to trigger a loose wet avalanche on similar slopes. Expect these conditions to develop first on E-S aspect but become prevalent in all locations as the day continues. Don’t underestimate these loose wet avalanches. Avalanche observations form the past week have reported small loose wet avalanches gouging into older snow layers, growing large, and traveling further than normal.

Cornices have grown large over the winter in many locations. As the temperatures warm and the sun comes out, these hanging blocks of snow will begin to droop and fail. It is very difficult to determine when and where this will occur. Do not linger in locations where cornices are above you.  Choose travel routes and techniques that minimize your exposure this difficult to assess overhead hazard.

We have received reports of isolated but very large deep wet slab avalanches over the last week in many of the Cascade West zones. This is a reminder that older deeper weak layers may still exist in the snowpack. These layers have become wet with recent warming. In most cases these avalanches appear to have been triggered by a cornice fall or a loose wet avalanche. Do not hangout in locations below very large avalanche paths where these low-likelihood high-consequence avalanches could occur.

Generally cold temps and radiational cooling should allow for a strong overnight freeze of the snowpack Saturday night. Minimal new snow was reported at NWAC weather stations Saturday. Locally higher amounts may have occurred in areas closer to the Cascade crest.

In most near and below treeline locations the surface snow consist of a melt-freeze crust. The thickness and strength depends on aspect and elevation. On shaded slopes above treeline pockets of cold dry surface snow may still be found. The upper snowpack is a combination of frozen melt-freeze crust, weak large melt forms, and strong rounded grains. Areas of weak older snow can be found in some locations, however we do not have adequate information about the distribution of these layers.

We have very limited information about older persistent weak layers on the east slopes of the Cascades. You are most likely to find a reactive persistent weak layer on shaded aspects or at higher elevations above recent rain events. Large cornice failures are the most likely way to trigger such a layer. If you have any information on snowpack conditions consider sharing your observations with NWAC on our public observations page.

Two common persistent weak layers seen in the Northeast Cascades are:

• 3/25 and 3/22: Buried surface hoar layers found on shaded aspects near and above treeline.
• 2/13 Facets above a firm and thick melt-freeze crust can be found in many locations near and above treeline. This layer is thought to be dormant at this time but may re-awaken with a substantial weather input.

Lower elevations further east of the crest have melted back for the season and no longer present an avalanche risk. 

Observations

An avalanche professional traveling in the Stuart Range this week reported a widespread loose wet avalanche cycle Thursday with warm air temperatures and clear skies. Above 6500’ dry snow was still found including lingering wind slabs. This resulted in a skier triggered wind slab on an E aspect at 7800’. Several large and very large (D2-D3) slab avalanches from earlier in the week were also observed.