New snow and strong winds Friday night will form fresh storm slabs. These will likely be most reactive in wind-loaded areas and where a crust has been buried. Also watch for sluffing in steep terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TONIGHT: Mostly cloudy, flurries. Accumulation 10-25 cm. Ridge wind strong to extreme, southwest. Alpine temperature near -5. Freezing level 1400 m.SATURDAY: Mix of sun and cloud. Ridge wind strong easing to moderate, southwest. Alpine temperature near -5. Freezing level 1500 m.SUNDAY: Mostly cloudy, flurries. Accumulation 5-10 cm. Ridge wind light, east. Alpine temperature near -5. Freezing level 1500 m.MONDAY: Mostly cloudy, flurries. Accumulation 4-6 cm. Ridge wind light, east. Alpine temperature near -7. Freezing level 1000 m.
Avalanche Summary
Thursday there were reports from Glacier National Park of a loose wet size 2 on a south aspect at 2100 m, and a size 4 wind slab that occurred overnight and is thought to have been cornice triggered on a north aspect at 2800 m.Wednesday there was a report of a natural cornice failure that resulted in a size 2.5 wind slab release (50 cm deep and 200 m wide) on a northeast aspect at 2600 m, north of Glacier National Park.On Tuesday in the neighboring Glacier National Park, all aspects were involved as natural loose wet avalanches ran size 2.5 to 3 between 1950 and 2700 m.Loose wet avalanches to size 2 were reported from all aspects between 1000 and 2300 m Monday. In the neighboring Glacier National Park, loose wet avalanches to size 3 were reported from solar (south and west) aspects to size 3 between 2000 and 2300 m. A size 1.5 storm slab was ski cut from a northwest facing feature at 2400 m.
Snowpack Summary
A thin surface crust is now present on all aspects to at least 2300 m. This crust likely goes even higher on south facing aspects, while 20-30 cm of cold snow can still be found on high elevation northerly facing features. There are now a few different crusts in the upper 50 cm of the snowpack, with only the upper, most-recently buried crust posing a concern with new snow in wind-loaded areas. There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 70 to 110 cm below the surface. This buried crust/surface hoar interface was widely reactive last week, but has not produced any avalanche activity in the last few days. It is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or a cornice collapse).Deeper persistent weak layers from December and January are dormant at this time.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.