Avalanche Forecast
Regions: Mt Hood.
Recent wind slabs are becoming more difficult to trigger, however shifting winds have transported snow to a variety of slopes above treeline. You could still trigger a wind slab on steeper wind-loaded slopes, so continue to travel with caution at higher elevations. In exposed terrain, recent snow may be stripped to a strong rain crust.
Discussion
Avalanche and Snowpack Discussion
Following rain and freezing rain Saturday, 10-12 inches of snow accumulated Saturday night and Sunday with strong WNW winds. Winds shifted to easterly and transported snow to a variety of aspects making wind slabs possible on all aspects. Mt. Hood Pro-patrol found fresh but stubborn wind slabs up to 2' deep near treeline. More importantly, wind slabs had developed on unusual aspects, cross-loaded slopes and formed on open slopes below treeline. Winds had scoured ridges to the most recent firm icy crust in many areas. We have no recent observations from above treeline due to the recent stormy conditions.Â
Snowpack Discussion
December of 2018 was fun (from a forecasting perspective) with three pronounced avalanche cycles, a couple different persistent weak layers, some rain events, and a flurry of human triggered avalanches to ring in the New Year. Most importantly, it seems that we made it through the last days of 2018 without anyone getting seriously hurt by an avalanche.
The deep (Dec 9) layer responsible for many of the avalanches early in the month no longer seems to be a problem in the western zones. That said, it is still possible to trigger an avalanche on its counterpart (or basal facets) in the eastern areas.
A widespread layer of surface hoar formed around Christmas. Late December storms preserved this layer in areas above the rain line and we have numerous (more than a dozen) reports of people triggering avalanches on it in the last three days. At least 4 people were caught and carried during this period, but so far we have no reports of serious injury. Most of these avalanches were soft slabs, D1-D2+, but there were several harder wind slabs in the mix.
It appears that the layer is most reactive and/or prevalent in the Crystal Mountain backcountry and in the mountains around Leavenworth and west of Mazama.
Surface Hoar can be an especially tricky and persistent weak layer. Read more about it here.
Avalanche Problems
Wind Slabs
Wind slabs formed over the weekend are gaining strength, becoming more difficult to trigger. Backcountry travelers and local professionals reported finding wind slabs in unusual locations due to shifting wind directions. You may still trigger wind slabs on convex rollovers, near the sides of cross-loaded gullies, and on wind drifted snow below ridgelines. These wind slabs have formed over a very strong freezing rain crust formed last Saturday to at least 7300 ft.
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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1