Temperatures are forecast to rise significantly early this week. This rapid increase in temperature will result in a spike in avalanche danger. For advice on how to manage these changing conditions please refer to the latest forecaster's blog.
Weather Forecast
Monday: Mainly sunny with valley cloud. An above freezing layer (AFL) is expected to develop between 1500 and 3000 m. Mountaintop temperatures should rise throughout the day. Winds are light from the northwest. Tuesday: Mainly sunny with valley cloud. The AFL strengthens with mountaintop temperatures climbing to at least +5. Winds are light from the northwest. Wednesday: Mainly sunny with valley cloud. The AFL will likely persist with mountaintop temperatures remaining above zero.
Avalanche Summary
There was a size 2 accidentally triggered slab avalanche in the Spearhead Range on Thursday. A thin wind slab was triggered near ridge top on a relatively low-angle slope, which then stepped down to a weak layer approximately 100 cm deep lower on the slope. This avalanche is suspected to have released on the early January surface hoar layer. We could see this weakness wake up this week as temperatures rise above zero in the alpine.
Snowpack Summary
The snow surface consists of thin new wind slabs, a sun crust, dry snow, or feathery surface hoar depending on aspect and elevation. Below this 40-70 cm of storm snow sits on a weak layer of surface hoar, facetted snow, and/or a crust. Snowpack tests on Wednesday continued to yield easy to moderate sudden planar, or "pops", results on this interface. No significant weaknesses have been reported recently below this in the mid snowpack layers. Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in steep, shallow, rocky terrain where more facetting has taken place.
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.