At higher elevations, Friday's storm is expected to form touchy wind slabs.
There is a lot of uncertainty about how buried weak layers are going to react to sun and warming this weekend. Use a conservative approach to terrain selection and watch for signs of instability.
Ongoing SW through NW winds have formed reactive wind slabs over the past few days. The storm on Friday is expected to form new wind slabs or continue to develop existing slabs in exposed terrain at higher elevations. These slabs are particularly reactive where they overlie buried surface hoar.
By Saturday morning, up to 50 cm of relatively unconsolidated snow will sit over the January 30 surface hoar. With warming and sun in the forecast, this snow may quickly settle into a reactive slab this weekend. There is a lot of uncertainty regarding the timing and spatial extent of this scenario but it is expected to be most likely in the eastern part of the region which received more recent snowfall. Treat open slopes at and below treeline with extra caution.
A ridge of high pressure builds on Saturday bringing dry and sunny conditions with mild temperatures.
Friday Night: Snowfall 5-10 cm, moderate SW wind, treeline temperature around -6 °C.
Saturday: A mix of sun and cloud, moderate to strong NW wind, freezing level reaching around 1500 m.
Sunday: Mainly sunny, light to moderate W wind, freezing level may reach over 2000 m in the late afternoon with an inversion.
Monday: Mainly cloudy with sunny breaks, moderate SW wind, freezing level over 2000 m in the morning with an inversion, breaking down through the day.
On Thursday, ski cutting triggered size 1-2 wind slabs mainly on NE aspects above 2100 m elevation. Widespread natural loose dry activity up to size 2 was reported just north of the region.
Human triggered storm and wind slabs up to size 2 have been reported each day this week, mainly at higher elevations on north through east aspects. Loose dry avalanches were also being reported in steep terrain features.
Prior to Friday's storm, up to 35 cm of snow from last Sunday buried the January 30 interface which consists of a melt freeze crust at lower elevations and on solar aspects extending into the alpine and widespread surface hoar in sheltered areas at and below treeline which is typically up to around 20 mm in size and very weak in some places. Prior to Friday's storm, the older storm snow had not formed a slab in most places except for where it was wind loaded. With warming and sun this weekend, rapid settlement is possible and this may result in the formation of a more widespread reactive slab over the weak surface hoar and crust. Ongoing wind over the past week has formed reactive wind slabs in exposed terrain at higher elevations and new wind slabs may build during Friday's storm.
A crust/surface hoar interface from mid-January was down around 50 cm prior to the new snowfall and has been dormant recently but like the more recent weal layer, there is still some concern that this layer may also wake up with some warming and sun.
The early December crust/facet persistent weak layer is buried down 100-200 cm and has been responsible for significant avalanche activity in this region during the first half of January. The layer is now considered dormant, but still remains a concern and we continue to track it in the snowpack. See the most recent forecaster blog on how to manage this layer, as it may come into play again later this season.
Check out this great video from Whitewater for a detailed look at the snowpack in that part of the region.
