Lingering storm instabilities will persist for several days, especially in the alpine. Human-triggering remains likely and conservative decision-making remains critical.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
A ridge of high pressure will build over the interior on Tuesday. Mostly cloudy conditions are expected but sunny breaks are possible. Light scattered flurries are expected in the morning but things should dry out by the afternoon. Alpine winds should remain light. Freezing levels on Tuesday are expected to be around 1600m but should fall to near valley bottom Tuesday overnight. On Wednesday, mainly dry conditions are expected with a mix of sun and cloud. Freezing levels are forecast to climb as high as 2000m by the end of Wednesday. Thursday might be the first day with a lot of sun and freezing levels are forecast to climb to around 2500m.
Avalanche Summary
Widespread natural, human-triggered, and explosive controlled avalanches up to size 3 were reported on Friday through Sunday. This includes both storm slabs and persistent slabs. Many avalanches started dry and ended wet, running to valley bottom. On Tuesday, natural avalanches remain possible at upper elevations but are generally not expected. Human-triggering remains likely and travel in avalanche terrain is not recommended until the storm slab has had a chance to stabilize.
Snowpack Summary
60-100cm of recent storm snow sits over the late-Jan weak layer at higher elevations. This snow is expected to be settling rapidly with the warmer temperatures. Rain has soaked the snow surface up to around 1900m and moist snow is reported to at least 2200m. Strong SW winds have formed wind slabs in exposed leeward terrain features. The storm slab sits on an old rain crust at lower elevations, variable surface hoar, and/or wind affected surfaces at higher elevations. The mid-January surface hoar is typically down 80-120cm and has been very reactive in some areas. The mid-December weak layer is down around 1.5m but has generally been unreactive.
Problems
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.
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.