Avoid all avalanche terrain during periods of heavy loading from new snow and wind. This storm will be a good test for the deeply buried persistent weak layer and very large natural avalanches are possible Tuesday.
New snow combined with strong southwest wind is expected to initiate a natural avalanche cycle that may involve layers buried deep in the snowpack. The storm is expected to produce 10 to 15 cm by day break and another 10 to 15 cm throughout the day Tuesday.
Tuesday's storm will be a good test for the late October facet/crust layer near the base of the snowpack. There is very little recent information about the sensitivity and distribution of this layer.
A storm begins to bear down on the region Monday night and is expected to deliver a significant amount of new snow and heavy wind through Tuesday evening.
MONDAY NIGHT: Snow, temperature around -15 C, strong to extreme southwest wind, 5 to potentially 15 cm of snow.
TUESDAY: Snow, heavy at times, 10 to 15 cm of snow expected during the day, temperature around -12 strong to extreme southwest wind. Potential for another 5 to 10 cm of snow Tuesday night.
WEDNESDAY: Broken cloud cover, daytime high temp around -10 C, light wind generally out of the south, trace of snow possible.
THURSDAY: Scattered cloud cover, daytime high temp around -12 C, light wind generally out of the west, trace of snow possible.
Tuesday's storm adds a significant new load to our juvinile snowpack in the form of new snow and wind. A natural avalanche cycle is expected and the deeper weak layers in the snowpack are guilty until proven innocent. We may see some deep natural avalanche activity Tuesday when the storm is in full force.
Avalanche control work on Saturday produced many large wind slab avalanches on NE facing features around 1700 m. Most of these avalanches stepped down to weak facets and rocks.
On Nov 30, a size 2.5 skier-remote persistent slab was reported on the MIN (see report here). The avalanche was triggered from around 100m away, by a group of 5 riders on an east aspect at 1400m. The avalanche was suspected to have failed on an early-season facet/crust layer.
As of Monday afternoon, the White Pass has picked up 5 new cm of snow. 5 to 15 additional cm are expected tonight and then as much as 15 cm is incoming tomorrow with strong to extreme southwest wind. This combo will form a fresh round of storm slabs that could be quite touchy, especially during the storm.
Snow depth at treeline is approximately 80-120 cm, depths in the alpine range from 100-200 cm.
A facet/crust layer can be found near the bottom of the snowpack. This layer was reactive to human triggering last week with a notable skier-remote avalanche on November 30th. Tuesday's storm will be a good test for this interface.
