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
5-10mm of 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 and mostly cloudy but sunny breaks are possible. Freezing levels should be around 2000m and alpine winds light-to-moderate from the SW. 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 2800m. On Saturday, freezing levels should fall back below 2000m and this should be the start of a cooling trend heading into next week. 5-10mm of precipitation are 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. Activity has tapered off on Tuesday. The only report is of explosives triggering a size 3 avalanche with a slab depth of 200cm. In the North Columbia region, isolated natural activity was reported on Tuesday. 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, 60-90cm of rapidly settling snow sits over the late-Jan crust/surface hoar layer. Rain has recently soaked the snow surface up to around 1700m and moist snow is reported to at least 2000m. 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 are expected to form in the alpine with the forecast strong winds from the SW-W and new precipitation. The mid-January surface hoar is typically down 80-120cm and has been recently reactive in many areas. 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.
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.