Confidence
Poor - Timing, track, or intensity of incoming weather is uncertain on Sunday
Weather Forecast
For better or worse, weather models are far from perfect. They have a particularly tough time with situations like the one we're in now. The models call for rapidly changing freezing levels, strong to extreme winds out of the SW and uncertain precip amounts. My best guess for the Purcells is 15 cm of snow. The big winds will likely get right to work Saturday night out of the SW with sustained strong values, gusting extreme. Freezing levels will spike Sunday and may rise as high as 1800m. Cooling will build in Monday and then Tuesday looks to be fairly dry. This is all fine & good, but I must admit that my confidence in any model is quite low for the short term, so, take this weather forecast with a grain of salt and be ready for rapidly changing conditions.
Avalanche Summary
Control work in the Dogtooths continues to produce avalanches running to ground on basal facets & depth hoar in high elevation terrain with light loads. Further south, large loads produced very little results at mid elevations with large loads. Friday's winds formed stubborn wind slabs 20 - 30 cm in depth which were largely unreactive to skiers.
Snowpack Summary
The Purcell's are one of the more complex & variable snowpacks in the province right now.The region has received 70 - 130 cm of storm snow in the last week. A few shears are persisting in the new snow, but show signs of healing. Winds have been predominantly out of the W, SW, but some stations have reported NW winds in the last 24 hours. I've received obs of surface snow that is untouched by winds, and other obs where winds have produced a wind slab avalanche cycle. It's tough to put a pattern on what's happening out there. The reality is that it's highly variable drainage to drainage.The Friday (Jan.) 13th Surface Hoar is still reactive in compression test, producing moderate sudden planar results.The mid-December surface hoar/facet combo is down around 70 cm on the E side of the range & 230 cm on the west side. I suspect it's still susceptible to human triggering in the shallow snowpack areas.
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.
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.
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.