A strong storm over the last few days with heavy precipitation including snow and rain with strong winds has created dangerous avalanche conditions. Be cautious if you are traveling in the back-country. Avalanches are running to valley bottom.
Weather Forecast
The heavy precipitation overnight will backoff to light today, and the strong winds overnight should become light today and then rise back to moderate on Saturday. Overnight at Rogers Pass we recorded 1cm of snow and 28.5mm of rain. Light snowfall and cooling temperatures are forecast for the weekend.
Snowpack Summary
55cm of heavy, high density new snow now sits on top of the low density previous storm snow at treeline. The recent high winds have formed this snow into wind and storm slabs at treeline and in the alpine. Below 1700m there was a combination of rain and snow which did not refreeze overnight.
Avalanche Summary
A cycle of avalanche activity that began on Wednesday caused by rapid loading of the new snow by the very strong winds, and rising temperatures, continued yesterday. Numerous avalanches were observed yesterday running to valley bottom from artillery fire and natural triggers, with many in the size 3.5 range.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.