Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to how the snowpack will react to the forecast weather.

Saturday night: Clear, decreasing northeast wind, alpine temperature -16 C.

Sunday: Clear, light northeast winds, alpine high temperature -5 C, freezing level 600 m.

Monday: Clear, light variable winds, alpine high temperature -1 C, freezing level rising to 2200 m in the southern half of the region.

Tuesday: Clear, light northeast winds, alpine high temperature 0 C, freezing level 1000 m. 

Avalanches are expected to become more reactive with a rapid warm-up and intense solar radiation.

Over the past several days, large (size 2) human-triggered avalanches have been reported releasing in a drifted snow/weak interface combination and breaking 20-80 cm deep. These avalanches primarily occurred on leeward features above 1400 m. Cornices have also grown large with the recent weather, and a cornice failure could trigger a wind slab avalanche on the slope below. 

Last week, there were reports of large (size 2-2.5) human-triggered avalanches failing on the March 1st surface hoar layer. Over the past two weeks, avalanches have been reported on an earlier surface hoar layer from February 19th as well as a deep persistent slab failing on basal facets. This pattern highlights how shallow avalanches in the surface snow have the potential to strain multiple weak layers in the snowpack and release larger avalanches.

Temperatures are forecast to rise from -25 C to -5 C in the span of 24 hours and with intense solar radiation on Sunday. This significant warm-up is expected to rapidly destabilize surface snow and cornices as well as add significant strain to buried weak layers. 

Over the past few days, strong easterly winds drifted the 15-30 cm of recent snow into wind slabs in a reverse-loading pattern. Wind slabs will likely be more reactive where this snow rests on a weak layer of surface hoar and/or a crust on solar aspects. Cornices have also grown large with the recent weather, and a cornice failure could trigger a wind slab avalanche on the slope below.

Loading from new snow and wind has made several deeper weak layers problematic over the past week. A surface hoar layer from March 1st may be found 40-80 cm deep, and another combination of surface hoar and sun crust from February 19 may sit 60-90 cm deep. These layers seem to be most sensitive to human triggering at treeline elevations. 

A couple of weak layers that formed in January are buried in close proximity to one another 80-140 cm below the surface. Below that, an early season crust/facet layer lurks at the base of the snowpack. Sunday's warm-up may have the potential to re-awaken these deeper layers.

• Stay off recently wind loaded slopes until they have had a chance to stabilize.
• Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.