Expect new snow and strong winds to form storm slabs and grow cornices. Sloughing, and cracking around skis and sleds are signs that the new snow is bonding poorly to the old surface. Avoid wind loaded areas with pillowy or chalky looking snow.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
TONIGHT: Snow. Accumulation 10-15 cm. Ridge wind strong to extreme, southwest. Temperature -12. Freezing level valley bottom.SUNDAY: Snow. Accumulation 5-10 cm. Ridge wind moderate to strong, west. Temperature -8. Freezing level valley bottom. MONDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light to moderate, southwest. Temperature -8. Freezing level 700 m.TUESDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light to moderate southwest. Temperature -6. Freezing level 900 m.
Avalanche Summary
From Tuesday through Friday this week, there have been numerous reports of skier triggered slab avalanches up to size 2 on predominantly steep, southeast to southwest-facing features between 1600-2000 m, that failed on the mid-February crust. As well as explosive control results up to size 2, and a remotely triggered (from a distance) pocket of hard wind slab (size 1) near ridge top. On Monday, natural wind slab avalanches to size 2.5 were reported on a southwest through northwest aspects between 1800m and 2400m.Last weekend (Feb 17 & 18) there was a report of a wind slab release stepping down to deeper weak layers and triggering a size 3.5 persistent slab, on a south west aspect near 2300m. Although deeper, persistent avalanche activity has become less frequent over the past week, light triggers in shallow rocky areas, as well as large triggers such as a cornice collapse or step down from a wind slab release, still have the potential to result in large destructive avalanches.
Snowpack Summary
About 10 cm new snow now covers the old snow interface which consists of sugary facets, as well as sun crusts on solar aspects and surface hoar on shaded, wind-protected slopes. Below this interface lies another interface, with similar character and distribution that was buried mid-February and is now 40-60 cm below the surface. This layer has been reactive in recent snowpack tests and several avalanches have been reported to have failed on this layer in the past week. Within the mid and lower snowpack are several persistent weak layers that are beginning to show signs of improving but still remain suspect. Two surface hoar/ crust layers buried in January are now 150-200 cm below the snow surface. At least one of these layers can be found on all aspects and elevations.Deeper in the snowpack (200 - 250 cm deep) is a facet/crust/surface hoar layer buried in December that is most prevalent at treeline elevations and below.Near the base of the snowpack is a crust/facet combo layer buried in late November.
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.