Northwest Coastal

Incoming strong winds and heavy snowfall have increased the danger rating to high.

Seek conservative terrain choices that avoid avalanche terrain during this period.

New snow and a buried weak layer combined have the potential to produce very large avalanches.

Saturday: Numerous large (size 2) wind slab and storm slab avalanches have been reported. These avalanches were located on north aspect terrain between the elevation bands of 1400 to 1600 m. A few of them were naturally initiated with most being either explosive or ski-cut triggered.

Friday: Another round of ongoing avalanche occurrences has been reported, as visibility has been limited these reports suggest that many more have been occurring. Numerous both natural and explosive triggered large (size 2-2.5) have been reported. These avalanches have all initiated within the 1500 - 1600 m range just below ridgetop features. One very large (size 3) avalanche ran 1000 m in length and the common theme of running far and fast due to firm surface conditions has been a common theme. A rain-on-snow event triggered loose wet avalanches 1300 m and below.

On Thursday A naturally occurring and ongoing avalanche cycle was observed by numerous operations. Many of these avalanches were large (size 2). In the north of this forecast region, a very large natural wind slab avalanche (size 3.5) was reported.

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 simple non-avalanche terrain that is low-angle and well-supported. 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 15 to 40 cm Sunday night will add to 50-70 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.

Tonight a pacific storm front is scheduled to impact the forecast area and will be accompanied by heavy precipitation and strong southwesterly winds. Freezing levels are forecast to remain low initially, then begin to slowly rise to near 500 m. The brunt of the precipitation will likely occur on the direct western front ranges adjacent to the coast. As the storm moves over the region, precipitation amounts in areas removed from the coast are expected to be slightly lower.

Sunday night

Clouds and heavy snowfall begin in the late afternoon, with 10 to 25 cm of accumulation, alpine temperatures -6 °C. Ridge wind southwest 30 km/h gusting to 100 km/h. The freezing level slowly rises to 500 m.

Monday

Cloudy with snowfall, 10 to 25 cm of accumulation. Alpine temperatures -2 °C. Ridge wind southwest 80 km/h. The freezing level rises to 1000 m.

Cloudy with snowfall, 1 to 5 cm of accumulation. Alpine temperatures maintain at 0 °C. Ridge wind west 70 km/h. Freezing level 1500 m.

Cloudy with rain and snowfall, 5 cm of accumulation. Alpine temperatures 2 °C. Ridge wind west 50 km/h. Freezing level 2000 m.

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.