Avoid avalanche terrain Saturday. The snowpack will take time to adjust to significant new loading from snowfall, extreme wind and rain.
Ongoing snowfall will continue to build touchy storm slabs at higher elevations. Forecast extreme winds and strong temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. A widespread natural avalanche cycle is expected and overhead hazard is a significant concern Saturday.
Likelihood of loose wet avalanches will decrease as freezing levels drop through the day. Skier triggered loose wet may still be possible at low elevations Saturday morning.
As recently as Tuesday, explosives testing continues to periodically trigger a weak layer of snow at the bottom of the snowpack. Significant new loads from snowfall and rain will weigh heavy on these deep instabilities. Especially where rain saturates down to the basal weak layers, large slab avalanches can be expected Friday.
Friday night: 40-70 cm new snow in the alpine with rain below 1500 m. Extreme southwest wind. Freezing level 1700 m.
Saturday: 10-15 cm new snow in the alpine, with rain below 1300 m turning to snow as freezing levels drop. West wind easing from strong to moderate. Freezing level 1500 m dropping to 500 m through the day.
Sunday: Mix of sun and cloud with flurries bringing 10-15 cm new snow. Moderate southwest wind. Alpine high -6 C. Freezing level 300 m.
Monday: Sunny. Light north wind. Alpine high -6 C. Freezing level valley bottom.
Natural loose wet avalanches running on the January 20 crust were observed up to 1900 m on Friday. Storm slabs up to size 2 were reactive to explosive and skier control work 1900-2000 m. Alpine observations have largely been obscured by poor visibility through the storm but a widespread avalanche cycle is expected to be ongoing through Saturday.
The deep persistent problem most recently reared its head on Monday with large explosive loads producing a size 2.5. in shallow, rocky terrain. There is potential for the new snow loads to induce failures on these layers resulting in very large and destructive avalanches.
By Saturday morning, storm totals are forecast to reach 80-100 cm with another 10-15 cm falling though the day. Forecast extreme winds and strong temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. At lower elevations new snow will overly a crust from the preceding rain as freezing levels drop through the day.
Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range. Loading from new snow and rain will further stress these buried weak layers where they exist.
