Flurries and strong winds over the next few days will build fresh wind slabs in the alpine and exposed treeline areas. Watch for wind loading around ridgecrests and steep rollovers.
Forecast overnight flurries and strong winds will contribute to new wind slab development. Freshly wind loaded pockets will be most reactive to human triggers.
Steep sheltered slopes at lower elevations remain capable of producing human triggered storm slabs particularly in parts of the region where more than 30 cm of recent snow sits over surface hoar.
Some very large and destructive avalanches have been sporadically failing on deeply buried weak layers, predominantly on north through east aspects in the alpine. The bulk of events occur during periods of rapid loading by new snow or wind, or are triggered by very large loads (wind slab avalanche, cornice or snowcat). Human triggering can be possible from thin, rocky areas.
Wednesday night: Flurries bringing a trace to 10 cm new snow. Moderate to strong southwest wind. Freezing level valley bottom.
Thursday: Mix of sun and cloud with chance of isolated flurries late in the day. Moderate southwest wind, increasing to strong. Freezing level 600 m.
Friday: Flurries bringing 5-10 cm new snow. Strong southwest wind. Freezing level 800 m.
Saturday: Flurries bringing 5-10 cm new snow. Moderate southwest wind. Freezing level 500 m.
Human triggered slabs size 1-1.5 have been reported treeline and below, possibly running on patches of buried surface hoar. Last weekend, natural cornice falls are suspected to have triggered a number of natural wind slabs up to size 2.5 on north to east aspects in steep open terrain around treeline, one of which is described in this MIN report from Friday.
Some very large and destructive avalanches have been sporadically running on deeply buried weak layers near the bottom of the snowpack, predominantly on north through east aspects in the alpine. On Tuesday, a natural size 2.5 was observed. It is suspected to have started as a wind slab in a thin rocky area before stepping down. On Monday, two deep persistent slab avalanches size 2-3 were triggered from thin snowpack areas by very large loads pushed by snowcats.
Extensive wind effect in exposed alpine terrain with scoured and pressed windward surfaces and hard wind slab in lee features. In sheltered areas, recent snow may sit over patchy surface hoar or crusts on solar aspects and below 1200 m.
A couple of weak layers that formed in January now sit in close proximity to one another 60-120 cm below the surface and continue to give hard results in snowpack tests. Below, an early season crust lurks at the base of the snowpack. Some large avalanches have been triggered on these layers, usually during periods of rapid loading by new snow or wind and by large loads or from thin, rocky areas.
