Avalanche Forecast

Moderate -

The ridge that has delivered beautiful cold and clear conditions the last few days begins to collapse on Wednesday. High cloud invades the forecast region Wednesday and Thursday ahead of snow that is expected to begin in earnest Thursday night. Total storm amounts look to be on the light side for precipitable water, but, the cold nature of the flow should keep the snow very dry and light. This pattern continues with dribs and drabs of snow expected as we move through the weekend.TUESDAY NIGHT: Freezing level at valley bottom, very light variable wind at most elevations with strong northwest wind at ridgetop, no significant precipitation expected.WEDNESDAY: Broken cloud cover, freezing level at valley bottom, light variable wind at most elevations with strong northwest wind at ridgetop, trace of snow possible.THURSDAY: Overcast, freezing level beginning at valley bottom creeping up towards 1000 m in the afternoon, light west/southwest wind, trace of snow possible during the day with 10 to 15 cm possible Thursday night.FRIDAY: Overcast, freezing level near valley bottom, light southwest wind at most elevations with strong southwest wind at ridgetop, 5 to 20 cm of snow.

On Monday a natural size 2.5 wind slab avalanche was observed on a steep south facing feature at ridgecrest (2700 m). The wind slab had a crown 60 cm in depth. A cornice failure produced a size 3.5 deep persistent slab on a northeast facing slope at 3000 m that ran for 2 km. The crown was reported to be up to 300 cm in depth which suggests it failed on the late October weak layer at the very bottom of the snowpack.Wind slabs to size 2.5 were observed Sunday on north, northeast, south and southwest facing terrain features between 1900 and 2800 m. These were the wind slabs that formed during Saturday night's extreme wind event.On Thursday explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a great MIN report from January 22nd that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check it out here.

Last weekend featured warmth & extreme wind out of the south, southwest and northwest. This left a robust crust (up to 4 cm thick) on steep south facing aspects and redistributed snow into wind slabs which are growing old, tired and likely only susceptible to triggering in extreme terrain. The warmth allowed 10 to 50 cm of snow to settle into a consolidated slab above the mid-January persistent weak layer (PWL) which is made up of large surface hoar that is most prevalent at and below treeline. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The snowpack is harboring a nasty weak layer near the ground composed of weak facets above a crust. This interface continues to produce sporadic avalanches that are very large and destructive. Avalanches triggered on this weak layer take the entire seasons snowpack with it and have resulted in numerous close calls and serious incidents. This layer is most likely to be triggered from zones where the snowpack is thin and weak. Rock outcroppings and ridge crests around large open slopes and bowls in the alpine are particularly suspect