North Columbia

A Special Public Avalanche Warning is in effect in this region.Ongoing warm temperatures Monday are expected to initiate natural avalanche activity and further increase the likelihood of large human triggered avalanches.

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The normal decrease in temperature with height has once again been replaced by an inversion.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 1600 m and 3300 m, light to moderate south/southeast wind, no snow expected. TUESDAY: Increasing cloud cover, freezing level at valley bottom with above freezing temperatures between 700 m and 2200 m, moderate to strong south wind, no snow expected during the day, 1 to 5 cm possible Tuesday nightWEDNESDAY: Broken cloud cover, freezing level at valley bottom, rising to 1300 m in the afternoon, moderate southwest wind, trace of snow possible.

We received observations Sunday of a natural avalanche cycle to size 3.5. 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. On Saturday natural avalanches to size 3 were reported on northwest though south facing terrain between 1800 m and 2700 m.Widespread avalanche activity occurred Thursday and Friday with numerous reports of slab avalanches reacting to both explosive control work and human triggering. All aspects were involved as avalanches ran to size 2.5 on the January 5th interface. Reports of ongoing remote triggering (from a distance) speak to the reactivity of this interface. Some of the notable themes that are emerging from recent activity include accidental and remote triggering, 'step down' avalanches, avalanches on surprisingly low angle/supported terrain, and wide fracture propagations.

The last series of storms left 40 to 70 cm of snow in their wake. Moderate to strong southerly winds previously formed wind slabs in upper elevation terrain. This snowpack is currently quite complex; there are three active Persistent Weak Layers (PWL) that we are monitoring. The first PWL is known as the early January interface, it is 40 to 70 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 60 to 140 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 down 90 to 150 cm below the surface and has been less reactive in recent snowpack tests but it may still be susceptible to human triggering, especially in alpine terrain features with a thin or widely variable snowpack.