Watch for ongoing wind loading and wind slab formation in exposed terrain at higher elevations.
A persistent weak layer of surface hoar remains a concern on northerly aspects around treeline in the Flathead.
Watch for recent and ongoing wind slab formation on Sunday in exposed high elevation terrain. Wind transported snow was observed on Saturday caused by northwest wind. The wind direction is expected to shift to the southwest on Sunday with a few centimetres of new snow in the afternoon.
Persistent slab avalanches are still possible due to a layer of buried surface hoar around 40-60 cm deep. This problem is tricky to pin down because of its spotty distribution (it isn't a problem everywhere). It has been most reactive recently in the Flathead with reports of rider triggering (see MIN post), whumpfing and propagation in snowpack tests.
Steep, north-facing open treed features that are sheltered from the wind are the most suspect. Check out this post from the field team for the type of terrain we are avoiding.
The first in a series of storm systems is forecast to reach the region on Sunday afternoon.
Saturday Night: Mainly clear, moderate SW wind, treeline low around -12 °C.
Sunday: Increasing cloud cover with light snow in the afternoon up to 5 cm, moderate SW wind, treeline high around -4 °C.
Sunday night: Snowfall 10-20 cm, moderate SW wind, treeline low around -5 °C.
Monday: Snowfall 15-30 cm, moderate to strong SW wind, treeline high around -1 °C.
Monday night and Tuesday: Periods of heavy snowfall continuing overnight and then easing during the day, moderate to strong SW wind, freezing levels reaching near 2000 m.
No new avalanches were reported on Thursday or Friday. On Wednesday, skiers were triggering small wind slabs. The Avalanche Canada field team reported whumpfing and cracking in places where the late-January surface hoar is still preserved and reactive, but they didn't see any new avalanches.
Last Saturday, there was a machine-triggered persistent slab avalanche on a surface hoar layer in an open gully feature in the Rolling Hills area.
10-30 cm of old storm snow has been redistributed by recent variable winds earlier in the week which has formed thin wind slabs. Reports from Saturday suggest wind transport continues but wind slabs are expected to be relatively small and isolated. In south-facing terrain, the recent snow sits on top of melt-freeze crusts, and in exposed terrain, the recent snow sits over firm, wind-affected surfaces.
A buried surface hoar layer may be found 30-60 cm deep on sheltered, north-facing treeline-type features. This distribution of this layer is spotty in nature but has recently produced avalanches, whumpfing, and snowpack test results in the Flathead. While it does not appear to be as widespread or reactive in the Lizard, it has been found in some locations.
The lower snowpack is well consolidated, with a crust/facet layer from early-December found near the bottom of the snowpack. It is currently considered dormant but could become active later this season. Check out the forecaster blog for more information.
