Avalanche Forecast

Wednesday's reports continue to show a general slowing down of avalanche activity with a few notable occurrences, like an anomalous natural size 2 near Ymir peak that may have failed on the early January surface hoar, considering its distance from the natural cycle on the weekend. A vehicle in the southern Valhallas triggered a size 1.5 on this layer as well.

On Tuesday, improved weather allowed for better visibility noting the widespread natural avalanche activity that occurred last weekend. Many of these avalanches failed on the early January surface hoar.

Explosive control results since this cycle have included large deep persistent slab avalanches up to size 3 and storm slabs to size 2. Human triggering and remote triggering remain possible, with 1700-2100 m and east-to-northeast aspects being the critical elevation band and aspects for the early January layer.

Up to about 10cm of new snow has accumulated on a thin rime crust throughout the region on all aspects and elevations. This will be an interface to watch with the next snowfall and/or wind loading.

Including the new snow, about 30-40 cm now has been settling and bonding to a mix of wind-affected and sheltered low-density storm snow above about 1700 m and a rain crust at lower elevations.

A weak layer of surface hoar now sits preserved 50 to 70 cm deep, especially prevalent in sheltered terrain at treeline. This layer has been identified as the failure plane in many recent avalanches in the region.

A facet/crust layer is down 60-90 cm (and 2-10 cm thick at TL elevation). Below this, the mid-pack is settled and consolidated.

A concerning and weak layer of facets and crust 20-50 cm thick make up the basal snowpack.

Thursday nightSome clearing. Light west or southwest winds increasing a bit and shifting decisively to northwest in the morning.

Friday

A mix of sun and cloud. Light to moderate northwest winds, potentially strong in the alpine. Treeline high temperatures around -4.

Increasing cloud with a short period of snowfall at the end of the day bringing up to 5 cm of new snow, ending quickly in the evening. Moderate to strong south winds, increasing over the day. Treeline high temperatures around -5

Mainly sunny. Moderate to strong northwest winds easing over the day. Treeline high temperatures around -4.

More details can be found in the Mountain Weather Forecast.

• Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
• Wind slabs are most reactive during their formation.