While temperatures remain unseasonably warm, treat the snowpack with an extra degree of caution.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Temperatures are very warm (freezing level peaking near 2500 m) on Thursday and Friday, before cooling on Saturday with the passage of a cold front. Light precipitation is expected on Friday, followed by 5-15 mm precipitation on Saturday. This tapers to flurries on Sunday. Winds are moderate SW, changing to NW on Saturday as the front passes through.
Avalanche Summary
No new avalanches were reported on Wednesday. On Tuesday, explosives triggered a size 3 avalanche with a slab depth of 200cm. A widespread avalanche cycle occurred on Friday through Monday during the storm. Human-triggering of the persistent slab and/or wind slabs remains possible.
Snowpack Summary
Recent storm snow appears to be settling and bonding with warm temperatures. SW winds have created areas of wind slab on some alpine and treeline lee features. Keep your eyes open for cornices, which may be sensitive to collapsing with the warm temperatures. The late-Jan crust/surface hoar layer, buried up to a metre deep, remains a key concern, as triggering this would produce a surprisingly large avalanche. The mid-January surface hoar is typically down 80-120cm and is unlikely to be triggered, apart from in a thin or rocky snowpack area. The mid-December weak layer is down over 120cm, but was generally unreactive through the storm.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.
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.