Warm temperatures rising well into the alpine, combined with periods of sun and a chance of rain, will make for touchy avalanche conditions. Minimize your exposure to avalanche terrain if the snowpack is becoming moist.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A pacific frontal system will affect regions to the west and north more significantly. High freezing levels will mean that precipitation will likely fall as rain. On Friday expect isolated wet flurries in the alpine, with some sunny breaks. Alpine temps are expected to reach 4'C with SW winds gusting to 60km/hr. Overnight forecast precipitation amounts vary from a trace to 10mm with freezing levels from 2500-3000m. On Saturday expect increasing sun in the afternoon, which may destabilize the new snow at higher elevations. Alpine temps will be 2'C with W winds gusting to 55km/hr. Overnight freezing levels are expected to lower to 1400m, which will hopefully provide some recovery. Sunday will be unsettled with a mix of sun and cloud, isolated flurries and freezing levels rising to 2200m.
Avalanche Summary
No new avalanches were reported on Wednesday, but visibility was poor. On Monday a size 3 was remotely triggered from a steep unsupported roll, and a size 2 was accidentally triggered by skiers. Both occurred on N-NE aspects around 2200-2300m and were 20 to 50cm deep. A solar induced natural avalanche cycle occurred Tuesday afternoon up to size 2 on southerly aspects, and explosive controlled size 2-3 slab avalanches were initiated from steep N-NE aspects above 2300 m.
Snowpack Summary
Warm temps, sunny periods and high freezing levels will make surfaces moist, with no overnight recoveries expected. At treeline and above storm snow amounts from last weekend vary. The NW part of the region received up to 60 cm while the Dogtooth received around 30 cm and the far south received close to zero. This dense storm snow sits over the mid-March interface which consists of a series of crusts, old wind slabs, facets and surface hoar. On a NE aspect at 2375m on Wednesday tests results showed that this interface was easy to trigger and likely to propagate. In exposed terrain, strong SW winds had redistributed new snow into wind slabs on leeward terrain features and slopes. Below this interface is the mid-February facet/crust interface. The mid-February layer has not been reactive in the Purcells but has been very reactive in the neighboring North Columbia region. Deeper persistent weak layers that have been dormant for several weeks are not currently a problem but still have the potential to wake-up with major warming or heavy loading. Persistent weak layers may be suspect in shallower snowpack areas.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.