We're going from cold and stormy to unseasonably warm and sunny in quite a hurry which is expected to de-stabilize our snowpack. Cornice failures and very large natural avalanches are possible as we head into the warm spell.
Warming temperatures will exacerbate this problem. 30 to 70 cm of storm snow fell across the region over the last few days which has been formed into slabs by strong southwest wind. Large human triggered wind slabs remain likely. The new snow may be resting on surface hoar and facets which could set up a scenario where wind slabs remain surprisingly touchy.
Persistent slab avalanches ran during the storm and the coming warm temperatures are combining with direct sunshine. This is combo that could easily lead to cornice failure and natural triggering of very large persistent slab avalanches running on the November crust.
Wednesday marks the first day that the cold storm snow will feel both above freezing temperatures and direct sun. Loose wet avalanche activity is expected to be widespread.
Wednesday looks to be warm right up into the alpine. Temperatures return to more seasonal norms Thursday and Friday before an Atmospheric River delivers what is expected to be heavy precipitation on Saturday.
TUESDAY NIGHT: Freezing level around 2500 m through the night, strong to extreme southwest wind, 1 to 5 cm of snow possible at ridge top with rain falling at most elevations.
WEDNESDAY: Mostly clear skies through the bulk of the day with cloud cover increasing after sunset, freezing level holding at 2500 m, strong to extreme southwest wind, no precipitation expected.
THURSDAY: Overcast, freezing level between 500 and 1200 m, moderate to strong southwest wind, 5 to 10 cm of snow.
FRIDAY: Overcast, freezing level between 500 and 1500 m, strong south/southwest wind, up to 5 cm of snow possible.
Warm temperatures and direct sunshine are coming our way. Natural avalanches are possible.
We've got some more details from the natural avalanche cycle that occurred during the storm Nov 28 through 30th.
In the North, around Bear Pass wind slabs from size 2 to 3 released naturally in steep alpine features. Several persistent slabs up to size 3.5 were observed which likely failed on the November 3rd crust.
Around Terrace, the Skeena and Bulkley valleys, moist avalanche debris from size 2 avalanches was observed. This makes sense as there was much less storm snow around Terrace when compared with the north.
The storm over the last few days produced 30 to 70 cm of snow above 500 m. Areas to the north and west of the region got the bulk of the snowfall.
The new snow may be resting on the late November surface hoar and facets which could set up a scenario where storm slabs are surprisingly touchy.
Strong to extreme winds generally out of the south/southwest have formed wind slabs in open features at upper elevations.
We're learning that the early November crust is widespread, even in the alpine and treeline elevations. You should be able to find it 25 to 50 cm above the ground.
The total snowpack depth is roughly 150 to 200 cm at upper treeline and alpine elevations. The bottom of the snowpack consists of several thick crusts. There could be weak snow developing around these crusts in colder inland parts of the region.
