Tricky winter conditions exist at higher elevations. Spring-like, convective weather directly influences the snowpack and avalanche hazard can change quickly. Use a conservative approach and watch for signs of instabilities.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
The current weather pattern is more winteresque than it has been all season. Im beginning to feel seasonally confused. Unsettled conditions expected as the next front passes. Behind this front, a moist onshore flow will be directed to coastal regions bringing precipitation and strong winds, especially to upslope areas. Wednesday will see a mix of sun and cloud, strong westerly ridgetop winds and freezing levels rising to 1500 m. On Thursday, anywhere from 10-20 mm of precipitation is expected with strong west winds and freezing levels near 1500 m. On Friday a strong ridge of high pressure will build and bring clear sunny skies accompanied by rising freezing levels to 2500 m.
Avalanche Summary
No recent observations. On Monday, no natural activity was reported but numerous size 1 storm slabs were easily triggered by the weight of a skier, especially in areas that saw some wind effect.
Snowpack Summary
Upper elevations have received 25-40 cm of recent storm snow. The new snow sits on a variety of old snow surfaces including crusts, facets and spotty surface hoar which was buried on April 10th. This interface has shown a poor bond and has been reactive naturally and to human triggers. Moderate to strong south west winds has redistributed the recent storm snow into wind slabs on leeward slopes and behind terrain features. The mid-March persistent weak interface has been producing hard but sudden planar results in snowpack tests. This remains a concern in the region. There may be a low probability of triggering this layer, however; if it is triggered the consequence would be high. Large looming cornices may become weak with solar radiation and daytime warming. If a cornice fails it could trigger a large avalanche from the slope below.
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.