Copious precipitation with balmy mid-mountain temperatures means certainty about dangerous avalanche conditions increases with elevation. Travel in the alpine is not recommended!
A crust / facet layer from November was buried 50 to 100 cm before the storm. Conditions have lent well to cleaning out and stabilizing the problem, but it may still be possible to trigger, particularly in thin-to-thick areas in the alpine.
30 - 60 cm of new snow is expected to build a serious storm slab problem for Wednesday. Expect accumulations, wind loading, and most importantly, avalanche danger, to be greatest in the alpine.
Last Wednesday, a size 3 avalanche stepped down to a persistent weak layer near Allison Pass. See photo captions for more details.
Although observations are scant, it's likely the atmospheric river caused more persistent slab activity where this layer exists up high, and wet loose activity everywhere else there is snow.
Looking forward, a switch to heavy snowfall at higher elevations should form a reactive storm slab problem for above-threshold areas on Wednesday.
35 - 60 cm of new snow should accumulate above 1500 m by end-of-day Wednesday, mostly overnight, with amounts increasing with elevation. This will cover a rain-soaked snowpack that was 80 - 140 cm deep abefore the storm. There's not much snow below 1500 m.
A crust with facets, formed in mid-November, exists about 50 to 100 cm deep. Although all the rain ought to have cleaned out this problem where it existed, it's hard to gain total confidence in it with limited observations and as loading continues.
Tuesday Night
Cloudy with increasing, warming precipitation bringing 30 to 50 cm of new snow to the alpine, diminishing with elevation with rain below about 1500 m. 50 km/h southwest ridgetop wind. Treeline temperature -2 °C. Freezing level 1400 m.
Wednesday
Cloudy with easing flurries bringing 5 to 10 cm of new snow. 40 to 60 km/h west ridgetop wind. Treeline temperature -5 °C. Freezing level 900 m.
Thursday
Mostly cloudy with wet flurries bringing about 5 cm of new snow to high alpine, light rain everywhere else. 40 to 60 km/h southwest ridgetop wind, increasing. Treeline temperature 2 °C with freezing level reaching 2000 m.
Friday
Mix of sun and clouds with scattered flurries and a possible few cm of new snow. 20 to 30 km/h southwest ridgetop wind. Treeline temperature -5 °C. Freezing level 900 m.
More details can be found in the Mountain Weather Forecast.
