Strong winds have made triggering wind slab avalanches possible at upper elevations. Be careful in drifted areas and assess open slopes and rollovers where a weak layer may be preserved.
Recent snow accumulations ranging from 5-15 cm have been redistributed by strong west winds into wind slabs on lee features at upper elevations and have have contributed to cornice growth. Cornice falls may trigger avalanches on the slopes below.
A weak layer of surface hoar buried Jan 11 buried 20-50 cm deep may be found on sheltered, open slopes near treeline. There is uncertainty as to the distribution and sensitivity to triggering of this persistent slab problem across the region. Deeper layers from early December and November can still be found in the snowpack and remain a cause for concern in thick to thin areas at upper elevations. The possibility exists for avalanches in the surface snow to step down to these layers.
Tuesday night: Partly cloudy, strong west winds, overnight flurries with trace accumulations, alpine temperatures near -10 C.
Wednesday: Mainly sunny, light northwest winds, alpine high temperatures near -12 C.
Thursday: Mainly sunny, light northeast winds, alpine high temperatures near -14 C.
Friday: Mainly sunny, light northeast winds, alpine high temperatures near -15 C.
Recent strong west winds are expected to have formed wind slabs in lee features at upper elevations that may be possible to human trigger. Over the last few days, operators in neighboring Glacier National Park reported several large (size 2-2.5) wind slabs releasing naturally on a variety of aspects. Cornices may be reaching their breaking point and can act as triggers on slopes below. Avalanches breaking in the recent snow have the potential to step down to deeper layers, creating larger and more destructive avalanches.
This MIN report from the Quartz zone on Thursday shows a reactive layer of Jan 11th surface hoar on north-facing slopes near treeline. It may be possible to trigger this layer in areas where the surface hoar has been preserved.
In the aftermath of the storm last Tuesday, we received reports of avalanches reaching size 3 in the central part of the region, lending support to the idea that some larger releases may have involved more deeply buried persistent weak layers. Although avalanche activity on these layers from early December and November has been isolated, the possibility exists for large triggers to reactivate these deeper instabilities.
Strong west winds have scoured windward facing slopes and redistributed the 10-25 cm of snow into wind slabs that may be possible to trigger. The snow and wind over the past week have contributed to notable cornice growth. Sun crusts may be developing on steep solar aspects.
30-60 cm of snow from the past week has buried a weak of layer of surface hoar from Jan 11th. This persistent weak layer is most suspect in sheltered, open slopes at treeline. This layer had produced sudden results in snowpack tests at treeline elevations in areas north in the region near KHMR and warrants careful evaluation. Limited observations across the region make it difficult to get a sense of the distribution and sensitivity of this problem.
Two deeper layers of surface hoar from December 13th and December 7th may still be found down 100-150 cm. The Dec 7th weak layer consists of a combination of decomposing surface hoar with a crust and faceted snow. Avalanche activity on these persistent weak layers has dwindled in the last week, with snowpack tests results trending to resistant and unreactive.
The lower snowpack is characterized by a notable rain crust from early November that is surrounded by a weak layer of sugary facets. It may still be possible to trigger with large loads in steep, shallow, rocky areas with a thin to thick snowpack.
