If more than 5 cm falls and the wind is strong enough to blow snow around, elevate, alpine danger to Considerable for Wednesday.
Confidence
Fair - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
A weak disturbance is expected to bring light precipitation for Tuesday night/Wednesday morning before the ridge rebuilds once again.Wednesday: Expect around 5 mm with the storm overnight Tuesday and into Wednesday morning with ridgetop winds 20-30 km/h from the NW. Alpine temperatures are expected to fall (max of -4C expected) and the inversion temporarily disappears.Thursday: Dry. Alpine temperatures should stay cool, around -4C, but rising late in the afternoon. Ridgetop winds around 20-30 km/h from the NW.Friday: Dry. The inversion returns with an above freezing layer from around 2200 to 3200m. Valley cloud and alpine sunshine likely. Winds 20-30 km/h from the NW.
Avalanche Summary
On Tuesday, two size 2.5 avalanches released on the same slope about 50 m apart. They failed to ground and it is thought that one released naturally and the other released sympathetically in response to the first. These have been the only avalanches reported since Saturday, when a size 2.5 deep persistent slab avalanche was reported to have failed naturally on a southeast facing slope at about 2300m. The avalanche failed on basal facets. On the same day, a snowmobiler triggered what appears to be at least a size 2 slab avalanche form a rocky alpine slope in the Allen Creek area. Little is known about this avalanche.
Snowpack Summary
Snowpack depths vary, but in general there is now 200 to 250cm of snow at tree line and as much as 300 cm in select places in the alpine. In the south and to the east of the region, there are still areas with a relatively thin snowpack. Roughly 100cm of well settled storm snow exists as a stubborn hard wind slab in many areas. Heavy wind scouring is reported to have occurred on many exposed windward slopes. Steep, sun exposed features are most likely seeing a daily melt-freeze cycle while surface hoar has been growing in shaded terrain. Below the recently formed storm slab, you may find surface hoar buried around January 8th, especially on shady slopes below treeline. A basal facet/crust combo (weak sugary snow above and below a crust) near the ground is still a concern in some areas, and was the culprit with some of the very large recent avalanches. Likely triggers at this interface would include cornice fall, rapid temperature changes or thin spot triggering on an unsupported alpine or treeline elevation slope.
Problems
Wind Slabs
Wind Slab avalanches are the 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.
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.