Kootenay Boundary

A touchy storm slab is expected to increase in size and destructive potential with snowfall forecast for Tuesday night.

High

Clear skies and valley cloud are forecast for Monday as the dry ridge of high pressure holds on for one more day. On Tuesday a Pacific front will move inland bringing up to 10cm of snow on Tuesday night and an additional 10cm on Wednesday. Ridgetop winds associated with the front will be strong and southwesterly. Freezing levels will hover around valley bottom on Monday and then rise to about 1300m with the passage of the front.

Over the past few days we've received a quite few reports of skier-triggered storm slabs in the size 1-2 range from the Nelson area. In one case, a size 2 storm slab was remotely triggered from a distance of 5 metres. Recently buried surface hoar was the culprit in all of these avalanches. Storm slab avalanches are expected to increase in size and reactivity with snowfall forecast for later in the week.

20-40 cm of recent storm snow has fallen in the last week. Warm temperatures and southerly winds have encouraged the formation of isolated pockets of soft slab at and below treeline. Thicker wind slabs are expected to be lingering in leeward features in the alpine. The new snow is resting on a widespread layer of surface hoar. These weak crystals sit above a melt-freeze crust on solar aspects or facets in shaded areas. Between 40 and 60 cm below the surface, the mid-December interface can be found. This layer consists of surface hoar, facets, and/or a melt-freeze crust. Recent snowpack tests from around Kootenay Pass area suggest that it could still be capable of producing human triggered avalanches. The early December rain crust can be found about 20 cm below that, up to an elevation of 1400m. This layer is thought to be gaining strength. The snowpack below this layer is generally strong and well-settled.