South Columbia

More snow Monday night will add to the storm slabs at upper elevations. These may become more reactive as the day warms or if the sun appears on Tuesday. Also watch for loose, wet activity on sunny and lower elevation slopes.

Moderate - Due to the number of field observations

TONIGHT: Cloudy, flurries. Accumulation 15-25 cm. Ridge wind light to moderate, southwest. Alpine temperature near -5. Freezing level 1000 m.TUESDAY: Mostly cloudy, flurries. Accumulation up to 5 cm. Ridge wind moderate to strong, west. Alpine temperature near -6. Freezing level 1600 m.WEDNESDAY: Mix of sun and cloud. Ridge wind light, south. Alpine temperature near -4. Freezing level 1700 m.THURSDAY: Increasing cloud. Ridge wind light, southwest. Alpine temperature near -2. Freezing level 2100 m.

On Sunday warming and sunny breaks initiated widespread natural storm slab and loose, wet avalanche activity in the recent storm snow, up to size 2, on all aspects from 1500-2300 m.Saturday saw widespread avalanche activity with natural, cornice, skier, and explosive triggered storm slab releases (size 2-2.5) on all aspects in the alpine and in immediate lee areas at treeline.Friday there were reports of several natural and skier-triggered storm snow releases (size 1) in steep and leeward alpine terrain. As well as several natural storm slab releases up to size 2 on alpine, northeast through southeast aspects.Thursday pockets of reactive wind slab up to size 1 in alpine lees were reported, as well as skier-triggered, loose, wet avalanches to size 1.5 up to 2100m on solar aspects and below 1900m on north aspects. There were also reports from neighboring Glacier National Park on Thursday of a loose wet size 2 on a south aspect at 2100 m, and a size 4 slab that is thought to have been cornice triggered on a north aspect at 2800 m.Tuesday there was a report of a natural size 2 wind slab avalanche that was observed on a north facing feature at 2800 m.

About 30-40 cm of new snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south-facing slopes), while 50-60 cm of storm snow can be found at higher elevations. Below 2400 m this new snow has a surface crust becoming moist or wet by the afternoon.Within the upper snowpack there are now a few different crusts with only the most recently buried posing a concern with the recent storm snow.There is some lingering concern around the mid-March Persistent Weak Layer (PWL) in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche activity in the past week. It is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think larger triggers such as; sleds, step-down from a surface avalanche or, a cornice collapse).Deeper persistent weak layers from December and January are considered dormant at this time.