A period of high danger continues. Expect heavy snowfall and strong winds that will continue both Friday night and into Saturday.
Seek conservative terrain choices, that avoid avalanche terrain during periods of high hazard. As the storm cycle continues, both the new snow and a buried weak layer combined have the potential to produce very large avalanches.
Expect continued snowfall and strong southwest wind to continue to build windslab.
Winds are expected to reach nearly 100 km/hr. Expect windslab to build lower in the terrain and downflowing wind to deposit snow near the base of steep cliffs and steep areas near ridgetops.
A series of storms are adding a significant load to buried weak layers in the upper meter of the snowpack. The primary layer of concern is a layer of surface hoar now buried 30-50 cm deep. This layer is spotty in distribution and is not present on the very western boundary of the region. Primarily the PWL is found inland and most likely to be a concern in sheltered and shaded openings around treeline.
The second layer is comprised of facets and in isolated areas surface hoar that was buried in late December. This layer is now down 70-120 cm. It has shown evidence of strengthening but remains on our radar as active loading continues.
Storm slabs will grow in size and sensitivity as the snowfall and wind increase. Expect the deepest and most reactive slabs to exist in wind-loaded terrain at upper elevations.
Keep in mind that storm slab avalanches have the potential to step-down to deeply buried weak layers, resulting in large and consequential avalanches.
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.
On Wednesday numerous reports from professional operations outline a myriad of notable both storm and persistent 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).
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 40-50 cm over Friday night and Saturday 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.
A strengthening pacific storm front is approaching the forecast area. Freezing levels are forecast to rise to near 1500 m and will be accompanied by strong southwesterly winds. 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 will be lower.
Friday night
Cloudy with snowfall, 20 to 50 cm of accumulation. Alpine temperatures slowly rise to -3 °C. Ridge wind southwest 75 km/h gusting to 100 km/h. Freezing level rising to 1200 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 easing to 20 km/h. The freezing level descends to 500 m.
SundayCloudy with some clearing and very light snowfall, with 1 to 5cm of accumulation. Alpine temperatures continue to cool with a low of -10 °C. Ridge wind southwest 50 km/h. The freezing level descends to the valley bottom.
MondayCloudy with snowfall, 5 to 15 cm of accumulation. Alpine temperatures maintain at -8 °C. Ridge wind southwest 40 km/h gusting to 60 km/h. Freezing level 500 m.
More details can be found in the Mountain Weather Forecast.
