Regions
Northwest Inland.
Wind slabs will be building at higher elevations: Dial back your terrain use on Tuesday and assess conditions carefully.
Confidence
Low - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
We're looking at a series of small systems impacting the region throughout the forecast period. The winter weather train keeps rolling into town! TUESDAY: 5-15 cm Monday overnight into Tuesday afternoon, strong southwest wind, freezing levels 1300m. WEDNESDAY: Lingering flurries (5cm possible) moderate south wind, freezing levels 1200m, alpine temperatures around -4 C. THURSDAY: Snow in the afternoon (5cm). Moderate south wind, freezing level around 1200 m with alpine temperatures around -3 C.
Avalanche Summary
On Sunday a Size 2 natural wind slab (average depth 40cm) was reported on a northeast aspect near 1800m in the south of the region. On Saturday, several wind slabs to Size 1.5 were reported on (east) northeast aspects in the north of the region.On Friday, loose snow avalanches were reported at treeline in steep terrain in the south of the region.The incoming weather will add load to the persistent slab, and human triggering remains possible in steep or unsupported terrain.
Snowpack Summary
Variable and unsettled weather has given 5-15cm of new snow in the past few days. Winds have been moderate to STRONG southerly, but most exposed surfaces are either heavily scoured or wind-pressed firm by now.Recent warming and sun have likely left a crust on solar aspects and below 1300 m (reportedly breakable crust below 1000m). Snow from the past week or so has settled into a 20-60 cm thick slab above an older crust interface. Reports suggest the bond to the crust is poor and has resulted in a reactive slab, in addition to weaknesses down 30-35cm within the storm snow itself (giving sudden planar results in snowpack tests).Weak sugary snow near the ground has been a dormant instability, but it may still be possible to trigger in steep rocky terrain.
Problems
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.
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.