Cornice failure, loose wet avalanches and even slab avalanches are possible as the upper snowpack feels the strong sun and warming temps for the first time today. Really watch your exposure to overhead hazard, it would be easy to be surprised by weird avalanches today.
10 to 35 cm of storm snow was heavily affected by shifting wind Wednesday that even got into tree'd terrain. As temperatures warm and the sun comes out over the next few days human or potentially even natural avalanches become more likely.
Weak snow at the bottom of the snowpack hasn't gone away unfortunately. As temperatures warm and the strong sun comes out over the next few days we need to be thinking about the potential for large destructive avalanches. Cornice failures become more likely during these kinds of conditions and a failing cornice could be the perfect trigger for the deep persistent slab. Human triggering would be most likley around steep rocky terrain features, or anywhere the snowpack is thin and weak.
Clear skies and warm sun for the next couple of days...
WEDNESDAY NIGHT: Freezing level at valley bottom, light southwest wind at lower elevations, moderate to strong northwest wind at ridge top, no precipitation expected.
THURSDAY: A few clouds, freezing level starting at valley bottom rising to about 1900 m, light southwest wind at lower elevations, strong northwest wind at ridge top, no precipitation expected.
FRIDAY: Clear skies, freezing level starting near valley bottom rising to about 2300 m, light to moderate southwest wind at lower elevations, strong southwest wind at ridge top, no precipitation expected. Freezing level holding around 1900 m Friday night.
SATURDAY: Broken cloud cover, freezing level lowering from 1900 m to 1500 m, light to moderate southwest wind, 4 to 8 cm of snow expected.
We're short on post storm observations, but control work produced storm slabs to size 1.5 Monday and Tuesday that were most problematic near ridge crest. On Wednesday a small storm slab was reported that may have failed on surface hoar.
The most recent deep persistent slab activity we know about is described in this MIN report from February 11 and this MIN report on February 9th. This layer may become reactive again with warming temperatures and the appearance of the strong late winter sun.
The 10 to 35 cm of snow from Sunday/Monday has been absolutely hammered by wind Wednesday as evidenced in this MIN submission. Wind was strong enough to get into below treeline features even. Wind stiffened slabs now rest on a variety of old surfaces including a firm crust on solar aspects, soft faceted snow, possibly surface hoar in sheltered areas, and old wind slabs near ridge crest.
A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17.
The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.
