Avalanche Forecast

Moderate - Timing or intensity of solar radiation is uncertain on Monday

The normal decrease in temperature with height has once again been replaced by an inversion. This classical pattern allows for cooler air to remain in the valleys while alpine temperatures rise to a degree or two above freezing. This setup should stick with us until Tuesday when warm air is expected to begin mixing into the valleys as an offshore front impacts the coast. The interior should remain mostly dry until a more robust system hits the south coast late Wednesday with precipitation spilling into the interior on Thursday.MONDAY: Scattered clouds in the morning, clearing throughout the day, freezing level at valley bottom with above freezing temperatures between 2200 m and 3000 m, light south wind, no snow expected. TUESDAY: Scattered cloud cover, freezing level initially at valley bottom, possibly rising as high as 2000 m. There may be a slight inversion, stay tuned for details. Moderate to strong southwest wind, trace of snow possible.WEDNESDAY: Scattered cloud cover, freezing level at valley bottom, rising to 1400 m in the afternoon, light to moderate southwest wind, trace of snow possible.

We received observations Sunday of a natural avalanche cycle to size 3.5 in the neighboring Central Columbias. These very large avalanches were running naturally on southwest, south and southeast facing alpine features and are thought to have been triggered by warming alpine temperatures and direct solar input. Similar activity was reported from the southern Purcells where natural avalanches ran to size 2 on southeast facing alpine features.On Saturday control work produced storm slab avalanches to size 2 on south and southeast facing alpine features. A cornice failure was also reported from a south/southeast facing alpine feature.On Friday we received reports of a widespread natural avalanche cycle to size 3.0 that had occurred during the previous 48 hour period. It's suspected that these avalanches initially failed on the early January interface before stepping down to the mid-December and possibly late November weak layers. Some themes that are emerging from recent activity in the Purcells and neighboring regions include accidental and remote triggering, 'step down' release types, releases on surprisingly low angle, supported terrain, as well as wide fracture propagations.

The last series of storms left a variable 10 to 60 cm of snow in their wake. Moderate to strong southwest winds previously formed wind slabs in upper elevation terrain. This snowpack is currently quite complex; there are three Persistent Weak Layers (PWL) that we are monitoring. The first PWL is known as the early January interface, it is 10 to 60 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects. It is thought to be widespread at all elevations bands and has produced numerous recent large avalanches. The next PWL is the mid-December facet/surface hoar/crust combination that is now buried 40 to 100 cm deep and is most problematic at and below treeline. This interface is not thought to be present in the alpine.The most deeply buried PWL is the late November rain crust. It is found 90 to 150 cm below the surface. This layer is considered dormant but it may be triggerable in thin spots around variable snowpack areas in the alpine.