Regions
Northwest Inland.
The wet, warm, and windy storm will result in High avalanche danger.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Stormy conditions over the next few days. 10-15 mm of precipitation are expected Friday night combined with strong Westerly winds and freezing levels around 1600 metres. Another 10-20 mm of precipitation combined with very strong Southwest winds on Saturday as freezing levels spike up to about 2000 metres. The latest models are showing the Sunday storm moving faster and bringing another 10-15 mm of precipitation by late morning, and then becoming mostly flurries or showers as the freezing level creeps down below 1500 metres. Monday should continue to be mild with moderate winds and freezing levels dropping below 1000 metres.
Avalanche Summary
Periods of heavy snow or rain, strong ridge winds, and warming will probably tip off a natural avalanche cycle in parts of the region. We could see wet activity at lower elevations with storm/wind slabs where snow accumulates. There is also potential for deep persistent weaknesses to be overloaded producing isolated very large and deep slides.
Snowpack Summary
Warm temperatures have promoted rapid slab settlement and wet loose surface snow at lower elevations, while southwest winds continue to build slabs on leeward slopes with cornices overhead in exposed treeline and alpine terrain. A recent report from the Ashman area mentioned whumpfs and other signs of instability associated with roughly 30 cm of recent snow rapidly settling into a slab under warm temperatures and significant wind. A surface hoar layer buried at the start of January may be around 40-60 cm deep now. In the mid-pack, a crust weakness buried in mid-December seems to be unreactive for the time being. Near the base of the snowpack is the crust-facet combination buried in November that could remain problematic, especially in shallower snowpack areas with heavy loading and warming.
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.