The snowpack may take time to recover from the weekend warming and the buried surface hoar may remain reactive, especially in the west of the region where the overlying slab is thickest. Ongoing wind slab development should be expected in exposed high elevation terrain.
Recent strong winds from the SW through NW have formed reactive wind slabs in exposed terrain at higher elevations. These slabs are particularly reactive where they overlie buried surface hoar.
Cornices may remain weak from the recent warming.
20-40 cm of settling snow sits over the January 30 surface hoar. This layer was responsible for several natural and human-triggered avalanches over the weekend, and is expected to remain reactive on Monday. Treat open slopes at and below treeline with extra caution.
The warm air in the alpine is forecast to persist overnight and there is some uncertainty if it will linger into the morning. By midday, the warm air should have exited and alpine temperature are expected to return to below freezing.
Sunday Night: Mainly clear, light to moderate SW wind, freezing level as high as 2500 m with a temperature inversion.
Monday: Increasing cloud cover in the afternoon with light snow in the north of the region, moderate to strong SW wind, afternoon freezing levels reaching around 1500 m.
Tuesday: Mainly sunny, light to moderate W wind, freezing levels reaching around 1500 m.
Wednesday: A mix of sun and cloud, light to moderate NW wind, freezing levels climbing to around 2000 m.
On Saturday, several natural wind slabs up to size 1.5 were reported throughout the region. Ski cuts triggered a couple small slabs and some small loose avalanches in steep terrain. A skier remotely triggered a size 1.5 slab from 5 m away on a west aspect at 1900 m which failed on the late-January surface hoar down 55 cm in the deeper western part of the region. Explosives triggered a size 2 cornice which released a slab on the slope below.
20-40 cm of rapidly settling snow now typically overlies the January 30 interface which consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, widespread surface hoar in sheltered areas at and below treeline, and small facets in some areas. With the recent warming, the surface snow has settled into a cohesive slab over the weak layer and a new surface crust will likely form as temperatures drop.
Periods of strong wind over the weekend, mainly from the southwest through northwest, have formed reactive wind slabs in exposed terrain at higher elevations. Ongoing wind on Monday will likely continue to develop reactive wind slabs where there is still loose snow available for transport.
Several old surface hoar layers are now buried in the upper snowpack 40-70 cm deep. While these old layers appear to have gone dormant, there is still an isolated chance of avalanches stepping down to a deeper layer.
The early December crust/facet layer of concern sits around 80 cm deep in the eastern Purcells and shallow terrain, and up to 150 cm in the west. This layer produced numerous large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season.
