The warm, wet, and windy storm continues to result in HIGH avalanche danger.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Very strong Southwest winds and moderate to heavy precipitation is expected overnight and ending Saturday morning as the second of three pulses of moisture moves into the region. The North and East of the region may remain cooler due to the influence of the arctic air to the North. Freezing levels should be between 500 metres in the far north and 1800 metres in the Southwest. Cloudy with strong Southerly winds during the day on Saturday with light precipitation, and then moderate to heavy precipitation starting in the late afternoon or evening. Winds dropping to moderate on Sunday combined with light precipitation and freezing levels slowly dropping. A weak Low pressure system is expected to bring light to moderate snowfall on Monday combined with light Easterly winds.
Avalanche Summary
No new avalanches were reported on Thursday due to limited observations during the storm. There were a couple of size 1.0 storm slab avalanches on Wednesday that were triggered by skiers. The storm slab was reported to have settled into a more cohesive slab with the warming temperatures. Expect natural avalanche activity and avalanche size to increase with storm loading.
Snowpack Summary
The storm slab continues to develop and is up to 70 cm thick and sits on a variety of old surfaces including crusts, surface hoar, and old wind slabs. A crust can be found below about 1900m in the north of the region and below 2200m in the south of the region. At higher elevations the new snow has formed thick windslabs formed by strong Southwest winds. Several persistent weak layers can be found deeper in the snowpack that may be capped by the overlying crust at lower elevations. The mid-January surface hoar is buried between 60 and 100cm down and remains a concern at treeline and above. The mid-December surface hoar layer is now 100 to 140cm below the surface and appears to be slowly gaining strength.
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.