Improving visibility beckons us into the alpine, but we need to watch for fresh slab formation as northwest wind picks up Sunday. At and below treeline, 20 to 30 cm of storm snow rests on surface hoar which teeters on the brink of becoming a touchy storm slab problem.
A couple of weak layers formed in late November and early December are now sitting about 1 m below the surface. This layer may present as surface hoar, a crust, facets or a combination of those, depending on elevation and aspect. They can most likely be found in areas sheltered from the wind, but open to a view of the sky, such as near treeline.
20 to 30 cm of recent storm snow rests on a widespread layer of large surface hoar. The storm snow is teetering on the edge of becoming a potentially touchy slab problem, but it hasn't happened yet. Northwest wind Sunday is likely to form fresh sensitive wind fueled storm slabs in wind exposed features, especially steep pieces of terrain near ridge crest.
We’re entering a rather quiet period with no significant snow expected until Monday afternoon. The next 48 hours are marked by seasonally normal temperatures, potentially sunny periods and a bit of northwest wind at ridgetop.
SATURDAY NIGHT: Freezing level at valley bottom, light westerly wind largely confined to the high peaks, no significant precipitation expected.
SUNDAY: Scattered cloud cover at dawn building to overcast by sundown, freezing level at valley bottom, light west/northwest wind at most elevations with moderate to strong northwest wind at ridgetop, no significant precipitation expected.
MONDAY: Broken cloud cover, freezing level at valley bottom, moderate west/southwest wind, snow beginning late in the day, potential for 5 to 10 cm by Tuesday morning.
TUESDAY: Overcast, freezing level beginning at valley bottom rising to 1400 m by sundown, strong southerly wind, 2 to 10 cm expected during the day, 5 to 15 more cm possible Tuesday night.
Reported avalanche activity Friday was limited to small wind slabs and loose dry avalanches in steep features at treeline.
Reports from Thursday mostly describe sloughing and small loose dry avalanches up to size 1. Soft storm slabs propagating at ridgetops but breaking up quickly as they ran, were also limited to size 1.
Prior to the new snow, numerous natural, explosive and skier triggered avalanches size 2-2.5 on a variety of aspects have been reported recently throughout the region and in neighboring Glacier National Park. Some of these avalanches were triggered in areas of shallow snowcover or wind slab and stepped down to the persistent November layer resulting in avalanches large enough to injure or bury a person.
20-30 cm of new snow has covered a widespread layer of large, feathery surface hoar crystals. The new snow can be expected to gain cohesion and settle into a slab in the mild temperatures, especially at treeline and below.
The new snow also buried soft wind slab found in the lee of features such as ridge tops, ribs and gulleys.
A weak layer formed in late November is now buried around 1 m below the surface. This is the layer of concern relating to the persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. It can most likely be found in areas sheltered from the wind, but open to a view of the sky, such as near treeline. Below this, variety of crusts from late October are buried deeper in the snowpack.
