Regions
Northwest Inland.
Please check out the new Forecaster's Blog for more detailed information on incremental loading, and "The Tipping Point"
Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Light-moderate amounts of snowfall are expected Tuesday night into Wednesday morning. Ridgetop winds from the West near 75km/hr overnight, tapering off to 40km/hr from the NW on Wednesday. Thursday may bring some flurries, but mainly dry, cooler conditions with the associated ridge. Freezing levels will remain at valley bottom. Friday brings light snowfall, and changing moderate winds from the East.
Avalanche Summary
No new avalanches have been reported.
Snowpack Summary
About 20 cm of snow that fell over the past week sit on a variety of old surfaces. These surfaces include: melt-freeze crusts that exist on all aspects at lower elevations and on south-facing slopes higher up and well-settled powder on shaded aspects in the alpine. Weak surface hoar crystals (size 3-4mm) are sandwiched between the old surfaces and the newer snow and have recently shown easy compression test results. The distribution of the surface hoar seems to be up to treeline on all aspects and on sheltered features in the alpine. This upper snow pack structure will be the big thing to watch as the overlying slab develops. I expect to see gradually increasing reactivity in the surface hoar interface with incremental loading and higher winds forecast for this week. Check out our Forecaster's Blog for some insight on incremental loading and the "Tipping Point" The mid and lower snowpack are generally well settled and strong.
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.