A lull in avalanche activity Thursday says more about savvy backcountry use than it does about drastic changes in our problematic snowpack. A local guide put it well: choosing "fat snowpack, low angle" lines is the strategy to employ. We need more than a subtle change!
Shifting winds have been acting on 10-15 cm of loose snow sitting on a freezing rain or rime crust, likely forming small wind slabs on a wide range of aspects in exposed areas. Southwest winds will be the driver on Saturday.
A persistent weak layer of surface hoar responsible for many recent avalanches exists 50-70 cm deep in the snowpack - prime depth for human triggering large, destructive avalanches.
Weak, faceted grains make up the basal snowpack. Where supportive to riders, a melt-freeze crust may be providing a bridging effect, making it more difficult to trigger deeper layers. Be especially suspicious of shallow, rocky, or cross-loaded areas with variable snow depths.
Aside from thin surface sluffs running on Wednesday's rime crust, no new avalanches were observed on Thursday.
Reports continue to show a general quieting down of avalanche activity on persistent weak layers, with a few notable occurrences, like an anomalous natural size 2 on Wednesday near Ymir peak that may have failed on the early January surface hoar, considering its distance from the natural cycle on the weekend. A vehicle in the southern Valhallas triggered a size 1.5 on this layer on Wednesday as well.
On Tuesday, improved weather allowed for better visibility noting the widespread natural avalanche activity that occurred last weekend. Many of these avalanches failed on the early January surface hoar.
Explosive control results since this cycle have included large deep persistent slab avalanches up to size 3 and storm slabs to size 2.
Human triggering and remote triggering the layers responsible for these avalanches remains possible, with 1700-2100 m and east-to-northeast aspects being the critical elevation and aspect ranges for the early January layer.
In exposed areas, northerly winds have been redistributing 10-15 cm of new snow, likely creating small wind slabs in a reverse loading pattern. In many areas the new snow accumulated on a thin rime or freezing rain crust that formed in the region on Jan 18, a new layer for us to watch over the near term.
Including the new snow, about 30-40 cm has been settling and bonding to an older mix of wind-affected and sheltered lower density storm snow above about 1700 m and to a rain crust from mid January at lower elevations.
A more problematic layer of weak surface hoar from early January now sits preserved 50 to 70 cm deep, especially prevalent in sheltered terrain at treeline. This layer has been identified as the failure plane in many recent avalanches in the region and remains reactive in snowpack tests.
Another problematic layer composed of a facet/crust combination is down 60-90 cm (and 2-10 cm thick at treeline elevation). Below this, the mid-pack is settled and consolidated.
A concerning and weak layer of facets and crust 20-50 cm thick make up the basal snowpack.
Check out an awesome state of the snowpack video update HERE.
Friday night
Increasing cloud. Light to moderate northwest winds, easing and shifting southwest.
Saturday
Becoming cloudy with a short period of snowfall at the end of the day bringing up to about 5 cm of new snow or just over, mostly in the evening. Moderate to strong southwest winds, increasing over the day. Treeline high temperatures around -5
SundayBecoming sunny. Moderate to strong northwest winds easing over the day. Treeline high temperatures around -4.
MondayMainly cloudy with isolated flurries in the afternoon. Light variable winds, mainly westerly, increasing over the day and overnight. Treeline high temperatures around -6.
More details can be found in the Mountain Weather Forecast.
