Where more than 30 cm of storm snow accumulates the avalanche game is on! Unless you know how to avoid travelling in avalanche terrain and minimizing exposure to overhead avalanche hazard, don't go.
A weak layer of surface hoar from mid-January was buried on open, sheltered slopes near and below treeline. I'm uncertain whether it will become active, but with new snow accumulating over the next several days it could be tested.
Storm snow amounts of 60 cm (or deeper) by Monday evening will be common in the region. Given moderate southerly winds, expect fresh windslabs. All this snow will be "upside down" with the warm (cohesive, slabby) snow on top. I expect Storm Slab avalanches to become more common, deeper, wider, and run further.
There may be a second surface hoar layer and temperature / density changes within this recent snow that serve as failure planes. Anticipate increased reactivity anywhere slab properties develop in this recent 5 to 45 cm of snow due to wind loading or warm temperatures as freezing levels rise.
A storm system off the BC coast will continue to pump moisture into the region on southwesterly winds.
SUNDAY Night: Around 10 cm more snow overnight with favoured areas getting 15 cm. Moderate southwest wind. Temps remaining warm with the zero degree elevation around 1000m, around -5 C at treeline.
MONDAY: Continued snow with another 15 to 25 cm expected Continued moderate southerly winds. Continued warm temperatures between 0 C and -5 C near treeline.
TUESDAY: More snow, 10 to 15 cm. More moderate SW wind. More temperatures at treeline just a few degrees below zero.
WEDNESDAY: The weather pattern changes as the wind shifts toward the northwest, temperatures cool, and the air dries out.
On Friday & Saturday avalanche activity was primarily small dry loose avalanches (sluffs) or small storm slabs. Two reports from the Monashees NW of Revelstoke are illustrative: this MIN from the 30th and this MIN from the 29th.
Initial reports from Sunday are of Storm Slab avalanches running within and at the bottom of the new snow.
Combining previous reports (e.g. those linked above running on surface hoar) with forecast snow fall amounts suggest an active natural cycle with increasing fracture depth and avalanche size. With poor visibility and people riding near treeline my spotlight is aimed at those surface hoar layers where avalanches could be deeper, wider, and run further than expected.
We're in a period of continued snowfall. With 10 to 30 cm today the storm snow totals are approaching 40 to 60 cm and more is forecast. With another 20 to 40 on the ground by Monday night or Tuesday morning some areas could approach the 100cm milestone! Moderate to strong southerly winds will build windslabs. Temperatures are warming so the coldest (lightest, least cohesive) snow is at the bottom, warmer (cohesive, slabby) snow is above.
The storm snow rests on the January drought layer: surface facets (sugary granules), surface hoar, wind hardened and sun crusts, etc.)
Observers continue to find a deeper preserved layer of surface hoar from earlier in January down 40-80 cm in sheltered, open slopes near treeline. Recent tests with sudden results suggests a need for continued assessment. Honestly, this storm is going to test the mid-January Surface Hoar layer (which I'm introducing as a new Avalanche problem).
The mid and lower snowpack is generally strong. Prolonged periods with no avalanche activity and unreactive snowpack tests results show the November & December layers (crust & facets) are dormant.
