Heavy snow is forecasted for the North Purcells on Saturday. Exercise extra caution during and after the storm.
Weather Forecast
20-25cm of new snow fell yesterday and overnight under the influence of light to moderate winds that trended from SE to SW and increased to gusts of 30km/h this morning. Up to 25cm of new snow is expected to fall in the north of the region on Saturday under light winds and a freezing level rising from 500m to 1000m. Southern parts of the region are expected to receive only trace amounts of new snow.
Avalanche Summary
Recent and forecasted snowfall are amplifying concerns for slabs and cornices forming at higher elevations and in exposed terrain. Recent reports include a natural Size 2 storm slab avalanche on a steep fan below a large alpine face in the Glacier Creek area. Check out the MIN report for for details including a photo.
Snowpack Summary
Snowfall from yesterday and overnight totaled 20-25 cm and contributed to a highly variable HS reported at 80-150cm yesterday. The new snowfall was accompanied by light to moderate winds, which will promote the growth of both cornices and touchy wind slabs that already exist in the region. Storm snow since Nov 13 has now accumulated to 60+cm and is settling into a cohesive slab over the hard Nov 13 CR. This crust is the primary weakness of concern and is expected to become increasingly reactive as the slab above settles and stiffens. Buried surface hoar has also been reported down 40cm on north aspects at upper treeline elevations, where it gave easy to moderate snowpack test results. The snowpack below treeline is creeping toward threshold for avalanches, but early season hazards such as hidden rocks, stumps, and open creeks remain the primary hazard here.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.