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Weather Summary

Cloud cover varied between partly cloudy to overcast this afternoon. Light winds blowing along ridgelines.

Avalanche Observations

Avalanche Observation Comments:

I did not observe any new avalanches today.

Snowpack Observations

Primary goals were to look at an older bed surface from the big avalanche cycle two weeks ago to see how these might behave when reloaded, to look at snow surfaces heading into the storm (how much did wind break up the weak layers, etc.), to check in on our solar persistent slab problems (ran out of time for this one), and see how much the warmth was impacting the snowpack.

Widespread avalanche activity on 12/11-12/12 resulted in a significant amount of terrain with exposed bed surfaces from that cycle. I've been thinking about how these will behave with additional loading. I poked into a bed surface in sheltered middle elevation and one in wind-exposed upper, both on shaded slopes. At middle, the slide had failed on 11/27 weak layer near the tail end of the storm and had received roughly 15 cm of snow since. This snow had faceted significantly and was capped by the rain crust + SH described below. This was all resting on a stiffer surface underneath. Plenty of coverage left to produce avalanches and a "great" new weak layer on top, yuck. Bed surfaces that look like this will undoubtedly be able to produce another round of avalanche activity. At upper elevation the one surface I was able to approach had been largely re-drifted by solstice winds. In places the original bed surface was exposed and scoured down to, in others stiff slabs rested on top of the bed surface. There is a degree of unpredictability/variability in how surfaces that look like this will behave. In general, I'm looking at bed surfaces as suspect and expect we will see plenty of repeat offenders during the upcoming storm.

The solstice wind-event moved around lots of snow and resculpted the snowpack in exposed terrain. Despite this, I was able to find a relatively impact snowpack in most places I looked. There are certainly some places where the wind helped things out, but mostly it just built some stiff drifts/slabs along ridgelines. Here, snow surfaces were wind polished, faceted, slippery windboard. Where the snow surface was less disturbed I found a pretty ugly upper snow package: the 12/11 rain crust sits 5-6cm below the snow surface and is accompanied by micro facet chains below. Ice lenses like this are excellent vapor barriers and gradiet concentrators. This layer doesn't exist in all of our mountains, but is pronounced in our southern mountains and is something we will be dealing with going forward. This rain crust had somewhat faceted away at elevations below the inversion, but was still present as an obvious ice lens once you climbed up 300-400'. On top of this sat some small facets, some standing 3-8mm SH, a bit more snow, another set of 3-8mm SH, and another light dusting of snow on top. Quite a 6cm package of snow! This will make avalanches when loaded.

Avalanche Problems

Primary concerns were the multiple persistent weak layers in the snowpack, recently wind-loaded slopes, and weirdness associated with warm air temperatures.