New snow, wind and warm temperatures are expected to make for touchy conditions. Small avalanches or cornice failures could step down to a buried persistent weak layer that has recently been responsible for large avalanches around Golden.
Confidence
Moderate - Freezing levels are uncertain on Monday
Weather Forecast
SATURDAY: Up to 10cm snow overnight, with another 5cm possible thought he day, rain expected at lower elevations, moderate to strong westerly winds, freezing level between 1200 and 1000m. SUNDAY: sunny with cloudy periods, light westerly winds, 1200m freezing level. MONDAY: sunny with cloudy periods, light westerly winds, freezing level between 2500 and 3000m, +5C at 2500m.
Avalanche Summary
We continue to receive reports of natural and skier triggered windslab avalanches from across the region. However, the January surface hoar layer remains the major concern, especially in the north Purcells where it has been responsible for several recent large avalanches. On Saturday a size 3 sledder-triggered avalanche occurred in the Gorman Creek riding area near Golden. Around the same time, a size 3.5 skier-triggered persistent slab avalanche occurred a few drainages to the south of Gorman Creek on a north-facing alpine slope. Similarly destructive persistent slabs are expected to remain possible to human triggering for the forecast period.
Snowpack Summary
Reactive wind slabs exist in the lee of ridges and open treeline features. Continued warm temperatures are expected to encourage settlement in the upper snowpack. A persistent weak layer of surface hoar and facets buried in early January is now typically down 40-90 cm. The layer is slowly getting harder to trigger in many areas, however, reports of whumpfing and some recent large to very large avalanches around Golden indicate this layer is still very much a concern, especially in the north of the region. In general, the lower snowpack below this layer is well settled and strong.
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.