The persistent slab will remain extra sensitive due to the unseasonably warm temperatures. Conservative decision-making remains important, especially in the alpine. If the sun comes out, use extra caution on south-facing slopes.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Light scattered precipitation is expected Wednesday overnight with freezing levels around 1500m and strong alpine winds from the SW-W. Thursday is forecast to be mainly dry with a mix of sun and cloud. Freezing levels should be around 2000m and alpine winds light-to-moderate from the W. Light scattered precipitation is possible Thursday overnight. Friday should see dry conditions with a mix of sun and cloud. Freezing levels should spike on Friday at around 3000m. On Saturday, freezing levels should fall back below 2000m and this should be the start of a cooling trend heading into next week. Light scattered precipitation is currently forecast for Friday overnight and Saturday with strong alpine winds.
Avalanche Summary
A widespread avalanche cycle occurred on Friday through Monday during the storm. Natural activity tapered off on Tuesday but human-triggered and explosive-triggered avalanches to size 3 were reported. A skier triggered a persistent slab avalanche on the mid-Jan layer in the Dogtooth range and went for a ride. Explosives triggered several avalanches on the late-Jan layer and one skier remote was reported on the same layer. Explosives also triggered a size 2.5 avalanche on the November crust/facet layer in an area that had previously slide and then reloaded. On Thursday, natural activity is generally not expected but is possible on steep south-facing slopes if the sun comes out. Human-triggering of the persistent slab remains possible, especially on steep slopes and wind loaded features in the alpine. If new wind slabs form overnight Wednesday, they may be touchy on Thursday.
Snowpack Summary
At higher elevations, 40-60cm of rapidly settling snow sits over the late-Jan crust/surface hoar layer. Rain has recently soaked the snow surface up to around 2000m and moist snow is reported to at least 2200m. Overnight cooling may be forming a weak surface crust at some elevations. Strong SW winds had formed wind slabs in exposed leeward terrain features. New wind slabs may form in the alpine with the forecast strong winds from the SW-W. The mid-January surface hoar is typically down 50-80cm and has been very reactive in some areas. The mid-December weak layer is down around 1m but its reactivity has been isolated recently. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It has generally been unreactive but one explosive triggered avalanche occurred on it recently in a reloaded area that had slide previously.
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.
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.
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.