South Columbia Avalanche Forecast
Mar 1st, 2019 4:51PM
Variable new snow amounts now blanket our wind slab problems. Keep recent wind loading patterns in mind, even if you're traveling through low density new snow.
Friday night: Cloudy with clear periods and isolated flurries with a possible trace of new snow. Light variable winds.Saturday: Sunny with cloudy periods. Light northeast winds. Alpine high temperatures around -18.Sunday: Sunny. Light northeast winds. Alpine high temperatures around -15.Monday: Sunny. Light northeast winds increasing over the day. Alpine high temperatures around -12.
On Wednesday, a few rider triggered wind slab avalanches up to size 2, on primarily northerly aspects at treeline and above were reported.Persistent slab avalanche activity on the mid-January weak layer has slowed down, but not stopped. This layer has created a low likelihood, high consequence scenario in the snowpack at treeline and below. Check out the great photos from a recent MIN. Take note of the low angle terrain and the light load of a single ski track that triggered this avalanche. This avalanche also stands out for its 2000 m elevation, which is considerably higher than most recent persistent slabs have been reported.
Recent strong northeasterly ridge-top winds have created wind slabs on lee features at treeline and above. Below this wind affected layer, older buried wind slabs exist on a variety of aspects. These remain a concern for overlying facets (weak, sugary snow), causing them to remain reactive for longer than is typical for a wind slab problem.There are two prominent weak layers in the upper snowpack. One was buried at the end of January, and the other mid-January. They are approximately 40- 60 cm and 60-90 cm below the surface. Both layers consist of surface hoar (weak, feathery crystals) and may be associated with a crust on steep, south facing slopes. These weak layers have been most prominent and most reactive below treeline.The lower snowpack is generally considered to be strong, except for shallow, rocky areas where the cold temperatures continue to facet (weaken) the snowpack.
Recently formed wind slabs can be found primarily on southwest aspects. Below them, hard, buried wind slabs on all aspects have continued to surprise riders. Thin to thick rocky areas are likely places to trigger these.
Avoid slopes that sound hollow or drum-like.Steep and rocky terrain are likely places to trigger buried wind slabs.Avoid wind loaded pockets, especially near ridge crests and roll-overs.
Reports of persistent slab avalanches are becoming less frequent, suggesting a lower likelihood, but high consequence avalanche problem. This problem requires discipline and careful terrain selection to manage effectively.
Use conservative route selection; choose moderate angled terrain with low consequence.Avoid low elevation cut-blocks where this layer is well preserved.Avoid steep, open and/or sparsely treed slopes at and below treeline.
Elevations:Treeline, Below Treeline.
Valid until: Mar 2nd, 2019 2:00PM