Storm slabs may be reactive to human triggering, especially in wind loaded areas, and at upper elevations. Watch for signs of instability such as whumphing, cracking and recent avalanches.
Weather Forecast
FRIDAY NIGHT - Mainly cloudy with clear periods / northwest winds, 10 km/h / alpine low temperature near -12SATURDAY - A mix of sun and cloud / northwest winds 10 km/h / alpine high temperature near -11SUNDAY - Mainly sunny / northwest winds 10-15 km/h / alpine high temperature near -9MONDAY - Flurries, 5-10 cm / south winds 20-40 km/h / alpine high temperature near -6
Avalanche Summary
On Friday, there were preliminary reports of a natural wind slab avalanche cycle to size 2.5 in the neighboring Glacier National Park region.On Thursday, there were several reports of human triggered wind slab, storm slab and loose snow avalanches, size 1-1.5, and natural loose and storm slab avalanches up to size 2.5.On Wednesday, a size 2 persistent slab avalanche was triggered by a cornice failure on a southeast aspect in the alpine. This avalanche reportedly failed on the late-January persistent weak layer.Persistent slab avalanche activity on the buried surface hoar layers (described in more detail in the Snowpack Summary) has tapered significantly. This has evolved into a low likelihood avalanche/high consequence avalanche problem at treeline and below.
Snowpack Summary
15-35 cm of recent storm snow is sitting mainly on wind slabs and facets (sugary snow), as well as surface hoar (feathery crystals) in sheltered areas and a crust on sun exposed slopes. There are two weak layers of surface hoar in the upper snowpack that were buried in late January and early February. They can be found between 40-90 cm below the surface. These layers consist primarily of surface hoar, though they may be associated with crusts on steeper, south facing slopes. These weak layers are most prominent at lower elevations, especially below treeline. The lower snowpack is generally considered to be strong, except for shallow, rocky areas where the cold temperatures continue to facet (weaken) the snowpack.
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.