Avalanche Forecast

On Wednesday numerous reports from professional operations outline a myriad of notable both storm and persistant slab avalanche occurrences. These avalanches were reported as natural, explosive controlled, and some accidentally triggered by skiers. One noted avalanche was a natural very large ( size 3 ) that scrubbed down to the ground. Primarily these avalanches occurred between 1700 and 1800 m on north-aspect terrain with most being large ( size 2 or greater).

On Tuesday, several natural storm slabs were observed (size 1-2) from the alpine and treeline. Numerous wet loose avalanches were observed at lower elevations where the precipitation fell as rain.

As the incoming storm will continue to add both mass and new snow supply to already touchy conditions. Riders should exercise restraint and patience as the new and past storm instability requires time to settle and bond. Choose low-angle well supported terrain and avoid steep and wind-loaded areas at upper elevations. Keep in mind the potential for deeper instabilities to produce large and surprising avalanches that will run far and fast.

Expected snowfall totals of 40 to 50 cm over the next 48 hours will add to 20-40 cm of recent reactive storm snow. At upper elevations, southerly winds are scouring windward areas and redistributing this storm snow into wind slabs in lee areas. Below 1000 m moist snow or a crust can be found at or near the surface.

A weak layer of surface hoar buried in early January is now down 30-60 cm. This layer is spotty in its distribution and is of greatest concern in sheltered and shaded openings at treeline.

Weak layers that were reactive over the Christmas and New Year's period have shown signs of bonding and gaining strength. These include a surface hoar layer buried on Dec 28 found 50 to 100 cm deep and a facet layer buried on Dec 23 found 70 to 120 cm deep.

Thursday night

Cloudy with heavy snowfall, 25 to 40 cm of accumulation. Alpine temperatures slowly rise to -5 °C. Ridge wind southwest 50 km/h gusting to 75 km/h. Freezing level rising to 500 m.

Friday

Cloudy with snowfall, 15 to 25 cm of accumulation. Alpine temperatures slowly rise to -2 °C. Ridge wind southwest 75 km/h gusting to 100 km/h. Freezing level rising to 1500 m.

Saturday

Cloudy with snowfall tapering in the afternoon, 5-10 cm of accumulation. Alpine temperatures cool to -6 °C. Ridge wind southwest 50 km/h gusting to 70 km/h. The freezing level descends to 500 m.

Sunday

Cloudy with some clearing and very light snowfall, with trace amounts of accumulation. Alpine temperatures continue to cool with a low of -9 °C. Ridge wind northwest 25 km/h. The freezing level descends to the valley bottom.

More details can be found in the Mountain Weather Forecast.

• Dial back your terrain choices if you are seeing more than 30 cm of new snow.
• Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
• Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.