New snow and strong winds Friday night will continue to build wind slabs at treeline and above. The new snow may bond poorly to the underlying crust. Watch for sluffing in steep terrain and loose, wet releases on sunny slopes.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TONIGHT: Mostly cloudy, flurries. Accumulation 10-15 cm. Ridge wind strong to extreme, southwest. Alpine temperature near -5. Freezing level 1200 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, light flurries. Accumulation 2-4 cm. Ridge wind light to moderate, southeast. Alpine temperature near -5. Freezing level 1500 m.MONDAY: Mainly cloudy, light flurries. Accumulation 2-4 cm. Ridge wind light to moderate, east. Alpine temperature near -7. Freezing level 1000 m.
Avalanche Summary
Wednesday there was a report of natural cornice failure that resulted in a size 2.5 wind slab release on a northeast aspect at 2700 m, while a skier was able to trigger a size 2 wind slab (40 cm deep and 100 m wide) on a recently buried crust on a similar aspect at 2400 m. There was also a report of a remotely triggered (from a distance) size 1 wind slab in an east-facing gully at 2300 m.On Tuesday a natural size 2.5 cornice failure on a north facing alpine feature did not produce any additional avalanche activity when it impacted the steep slope below. In a different location a skier intentionally trimmed a cornice so that it would fall onto a north facing slope at 2500 m. When the small piece of cornice impacted the slope it triggered a size 1.5 wind slab avalanche 30 cm in depth. A natural size 2.5 wind slab was observed on a cross-loaded east facing feature at 2400 m too.On Monday steep solar aspects produced natural loose wet avalanches to size 2 between 2000 and 2600 m. A size 3 natural cornice failure was also reported from a north facing slope at 2600 m.
Snowpack Summary
A thin surface crust is now present on all aspects to at least 2000 m. This crust likely goes even higher on south facing aspects, while 10-25 cm of cold snow can still be found on high elevation northerly facing aspects. 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 in wind-loaded areas.There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 60 to 100 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
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.