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RegisterDec 10th, 2020–Dec 11th, 2020
South Rockies.
The recent 10-20 cm of new snow has a poor bond to the underlying crust. Pockets of stiff wind slab may be reactive to human triggers at treeline and in the alpine, especially on leeward slopes and behind terrain features.
High pressure mostly dominates with some clouds and the chance of flurries on Friday then sunshine and cool temperatures for the weekend. Sunday evening should see the next change with possible snow forecast. Alpine temperatures will be near -10 and freezing levels will be in the valley bottom. Ridgetop winds will generally be moderate from the south-southwest through the forecast period.
On Thursday, natural wind slab avalanches were reported up to size 2. The recent storm snow is not bonding well to the underlying crust. Wind slabs may be reactive to rider triggers at treeline and above on Friday.
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10- 20 cm of recent snow fell at upper elevations while the rest of the precipitation came in as rain or freezing rain. Recent reports suggest that the freezing rain occurred from 1800m to 2000m “ish” with rain at lower elevations which may have destroyed the surface hoar at 2000m and below. All elevations are now hosting a burley crust under the new snow.
Up high, stiff wind slab exists on leeward slopes where the new snow deposits into deeper drifts, especially where the new snow sits above this recent rain/freezing rain crust, or the older melt-freeze crust found on solar aspects. Digging deeper in the snowpack two crusts exist from November. One down approximately 30 cm, just below the old surface hoar, and the other sits deeper (down 70-90 cm) and is widespread up to 2500 m. The deeper crust seems to be bridged by a well-consolidated mid-pack in most areas. These crusts have shown no recent reactivity in snowpack testing but remain on our radar moving forward.
The snowpack is generally thin, wind hammered, variable in wind-scoured areas, and tapers rapidly at lower elevations. Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches.