Quick report
- Red Flags
- Heavy Snowfall, Cracking, Collapsing, Poor Snowpack Structure
- Red Flags Comment
- <p>Was able to get cracking in the storm snow on slopes that held older, faceted snow on the snow surface. Did get a few collapses, but there didn't seem to be enough of a load on top of the facets to initiate collapsing.</p>
The first real storm of the year that falls onto an existing snowpack is always tricky as there is so much spatial variability. Most slopes facing the south half of the compass were bare dirt prior to this storm, so any storm snow instabilities should settle out quickly. The northerly aspects are more of a concern as many of these slopes had a patchwork of weak, faceted snow at the surface. In my field work today I was finding that the new snow was bonding reasonably well to the old snow where the surface was crusted. But on slopes where the old snow surface was weak and faceted, it was very easy to get cracking in the storm snow where the old snow was a reactive weak layer.
I would stay clear of avalanche terrain (slopes > 30°) on north-facing slopes at the mid and upper elevations as there is the potential for avalanches failing on this faceted layer. Avalanches may be triggered remotely and also occur naturally during any period of higher precipitation or any wind-drifting.
Photos are of cracking in the storm snow as well as a very weak pit on a NW aspect right at the transition point between mid and upper elevations.
For Friday's forecast, I am inclined to go with a Considerable danger rating for mid and upper elevation northerly aspects as the storm snow and fresh wind drifts are sitting on top of weak, faceted snow.
Snowpack
- Instability Comment
- <p>New snow was reactive with cracking on northerly slopes that had faceted snow on the old snow surface. Am selecting increasing danger with another round of snowfall expected overnight and into Friday.</p> <p>West/Northwest winds had relaxed by the time snowfall began ~6 am, but I was still finding a few shallow soft slabs of wind-drifted snow that were reactive to ski cuts with cracking. Winds are forecasted to increase overnight and into Friday morning - with plenty of low-density snow available for transport, I am expecting more sensitive wind drifts for Friday, especially at the upper elevations.</p>
Right-side up storm snow with denser snow (and some graupel mixed in) early in the storm followed by lower density snow. Some cracking in areas with with some wind-drifting making the storm slab a bit denser.