Observations in the region since the storm are limited to weather stations! Increase your caution as you reach your target of upper elevations where rain-wetted snow gives way to dry and where melt-freeze crust is thin or absent. This is also where settling storm snow is most likely to react to a human trigger.
Moderate to heavy rainfall at mid and lower elevations likely led to moderate to heavy accumulations of dry snow and dangerous surface instabilities forming in the alpine and possibly at upper treeline. The greatest concern is for wind loaded areas.
No new avalanches were reported in the region on Tuesday, which should be weighed against the fact no new reports of any kind were received.
A widespread cycle of natural wet loose avalanches occurred with rain in Kootenay Pass on Tuesday. Touchy surface instabilities composed of dry snow were likely widespread at any higher elevations that escaped the downpour.
Looking forward, elevations that saw moderate to heavy rain should see avalanche activity drastically reduce with overnight cooling periods. Areas where new surface crust is very thin and especially where it is absent will likely still harbour upper snowpack instabilities with wind slabs being the most likely.
As an indication of how much precipitation fell in the region since April 9, Kootenay Pass (1780 m) saw about 100 mm that equated to a roughly 30 cm increase in snowpack height. Strawberry Pass (1575 m) was closer to 50 mm and a 15 cm snowpack increase. A lot of rain has fallen in the Kootenay Boundary at most elevations, but there is some uncertainty about how much dry snow not capped or topped by rain crust exists at the region's highest elevations. Is it 40 cm? 90 cm? The potential for surface instabilities changes significantly between the two!
Where dry snow accumulations exist, even if topped by a thin crust, slab avalanche danger remains a concern. This is especially important in wind affected/loaded areas where the most recent wind slabs are likely to be found and are most likely to be human triggerable.
Whatever dry snow has accumulated has for the most part buried a widespread crust. The exception is on north-facing slopes at treeline and above, where the storm snow sits on old, faceted surfaces, and on surface hoar in some sheltered areas.
Where a thick rain crust or settled moist snow exists at the surface, avalanche danger will be tied almost exclusively to daytime warming and daily penetration of isothermal (melt) conditions into the upper snowpack. The wetter snow becomes and the deeper the wetness goes, the greater the hazard from wet loose avalanches.
The mid-snowpack is generally well-settled.
In some areas, the lower snowpack includes a layer of weak facets near the ground. No recent avalanches have been reported on this layer. However, we continue to track the layer and watch for any signs of it becoming active again.
Wednesday night
Mainly cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light to moderate northwest winds.
Thursday
Mainly cloudy with continuing flurries bringing a trace to 10 cm of new snow, rain below about 1400 m. Light west winds. Treeline high temperatures around 0 with freezing levels to 1800 m.
Friday
A mix of sun and cloud with isolated wet flurries or showers. Light southwest winds. Treeline high temperatures around 0 with freezing levels to 1800 m.
Saturday
Sunny. Light to moderate south winds. Treeline high temperatures around +1 with freezing levels to 1900 m.
More details can be found in the Mountain Weather Forecast.
