Danger will increase on south facing slopes during afternoon warming. Solar radiation could be enough to trigger stubborn persistent slabs or cause cornice failures. Conservative route selection remains crucial at this time.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Synopsis: The weather pattern is generally stable with a weak northwesterly flow. Some convective flurries may happen in the afternoon.Wednesday: Sunny with a few cloudy periods, flurries with a trace of precipitation, freezing level at valley bottom overnight, rising to 1300m in the afternoon, winds light from the south west.Thursday: Cloudy with flurries, some parts of the region may receive 5 to 10 cm of precipitation. No overnight freeze, freezing levels up to 1400m, Winds moderate, gusting to strong from the south west.Friday: Cloudy with flurries. Some parts of the forecast area may get up to 10 cm of precipitation. No overnight freeze and freezing levels may go up to 1600m. Winds light, gusting to moderate from the south west.
Avalanche Summary
A low probability, but high consequence avalanche problem plagues the Columbia regions. Highly destructive and largely unpredictable avalanches are possible right now. Smaller avalanches continue to step down to older, deep persistent weak layers producing large destructive avalanches. Commercial operators reported two size 3 natural avalanches yesterday and numerous 1.5 to 2.5 avalanches on all aspects. Neighboring regions are also reporting large destructive avalanches on south aspects as well as north and east aspects. There is real concern that the weak layers will become reactive with rising temperatures and solar warming..
Snowpack Summary
The weekend storm produced 30-40cm of new snow. Reports suggest there is moist snow up to 1800m on all aspects and higher on south facing slopes. Stiffer wind slabs may exist in immediate leeward features on NW through E aspects in exposed terrain in the alpine.Three persistent weaknesses contribute to a highly variable, fundamentally unstable, complex snowpack with step-down potential. The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human-triggers, but still has the potential to produce large avalanches, and we continue to see fractures stepping down to this layer. The mid-February crust/facet/surface hoar layer is typically down at least 1.5m and direct triggering has become unlikely. However, large loads like cornices or smaller avalanches stepping down can still trigger this layer and produce very large avalanches.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of 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 Slab.
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.