Expect touchy avalanche conditions at all elevations. Wind-kissed storm slabs have potential to propagate widely and loose dry avalanches are likely on steep, sheltered slopes. Stick to low consequence terrain.
We have uncertainty around residual reactivity of a few layers in the upper snowpack which have been largely dormant during the dry spell but may become reactive with new snow loads. These layers are detailed in the second paragraph of the snowpack summary.
New snow is is adhering poorly to previous surfaces, especially where it sits over surface hoar or a crust. As a result, storm slabs are touchy and have potential for wide propagation.
Loose dry avalanches run easily in wind sheltered areas where the snow hasn't formed a slab.
Read about the crust that never dies in our latest forecaster blog.
Found 100-180 cm below the surface with weak sugary crystals (facets) on top, this crust often wakes up as the weather changes, triggering large avalanches at all elevations including some unusual areas such as the middle of slide paths, open trees, and burns. With the added stress of this weekend's snow load, potential exists for storm slab avalanches to step down, resulting in very large and destructive avalanches.
The Monashees will see highest snowfall amounts out of this storm.
Sunday night: Snowfall 10-25 cm, moderate SW wind, treeline temperature around -7 °C.
Monday: Flurries up to 5 cm, light to moderate NW wind, treeline high around -9 °C.
Tuesday: Mostly cloudy with scattered flurries, moderate NW wind, treeline high around -13 °C.
Wednesday: Mostly cloudy, light wind, treeline high around -18 °C.
The theme during the dry spell last week was large cornice failures and wind slab avalanches size 2-3 on north to east aspects in the alpine. On Friday, wind slabs were reactive to explosives up to size 3 and skier traffic up to size 1. Dry loose avalanches were also observed up to size 2.
On Tuesday, a natural size 1.5 persistent slab was reported on an E aspect at 1900 m in the Monashees north of Revelstoke, likely failing on one of the surface hoar or crust layers 30-45 cm deep.
Deep persistent slab activity on the early December facet/crust layer slowed down during the dry spell. Most recently, two naturals were reported on Monday, size 2.5-3. Between January 20 and 23, numerous very large (size 2.5-4.5) deep persistent slab avalanches occurred on this layer, typically 100-150 cm deep.
New snow continues to accumulate over faceting wind affected surfaces in the alpine, a melt-freeze crust on steep solar aspects & low elevations and a widespread layer of large surface hoar crystals, especially prominent in shady, wind sheltered areas at elevations near the top of the previous valley fog layer (1200-2000 m). New snow is expected to adhere poorly at this interface.
There are three prominent layers in the upper snowpack which have been largely dormant during the dry spell but may become reactive with new snow loads. These include a layer of surface hoar down 20-30 cm, a layer of facets and/or surface hoar from early January down around 40-60 cm, and a thick layer of facets from the end of December down close to 1 m.
The primary weak layer that remains a widespread concern across the Columbia Mountains is a deeply buried crust/facet layer that formed in early December. It is typically down 100-180 cm, but as deep as 250 cm in wind-loaded terrain. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered. Check out our latest forecaster blog on the crust that never dies.
