Purcells

The storm is over and the new storm slab may take several days to settle and bond to the old surface. The mid-December buried surface hoar crust combination is expected to continue to be a tricky problem to solve.

Fair

Warm air that has been trapped in the alpine should move out and let the alpine cool down to about -5 by Thursday morning. The freezing level should also drop down to valley bottoms overnight, and stay there throughout the forecast period. Moderate Northwest winds overnight should become light Southerly during the day on Thursday. Valley temperatures dropping to about -18 by Friday morning with light winds and increasing cloud. Flurries or light snow during the day on Friday combined with light winds. Light snow overnight and during the day on Saturday with alpine temperatures around -8.

One natural avalanche size 3.0 on Wednesday from the North of the region on a South aspect that started from some solar warmed snow falling onto storm snow and then probably stepping down to the mid-December persistent weak layer. Explosives control work on Wednesday resulted in avalanches up to size 2.5 in the storm snow and up to size 3.0 in one case where the slide released and then went down to the ground. I suspect that natural avalanche activity will become less likely, and human triggering will continue to be likely-very likely.

There is a great deal of variability across the region. The West and South have received up to 60 cm of storm snow, quickly followed by high freezing levels and warm air up into the alpine. The North and East of the region have had 20-30 cm of cold dry new snow over the past few days with light Northeast winds, followed by some periods of solar radiation and warm alpine temperatures on Wednesday. The moist surface snow was sluffing naturally and triggering the storm slab in some areas on Wednesday. This new storm slab may be sitting on a patchy layer of surface hoar that was buried near the end of December. Deeper in the snowpack there is a persistent weak layer of surface hoar and crust that is now down about 60 cm. This persistent weak layer continues to likely-very likely to trigger from human activity.