Conservative travel is recommended at all elevations because of generally poor snow quality and uncertainty from limited data.
Confidence
Low - Due to the number of field observations on Friday
Weather Forecast
Cooler temperatures with light flurries are expected Friday and Saturday until the next warm and wet storm on Saturday night and Sunday.FRIDAY: Cloudy with flurries, accumulation 5-15 cm / Moderate to strong southwest winds / Alpine temperature -7 C / Freezing level 1300 mSATURDAY: Cloudy with light flurries, accumulation 2-5 cm / Moderate to strong southwest winds / Alpine temperature -5 C / Freezing level 1500 mSUNDAY: Flurries in the morning and rain in the afternoon, accumulation 10-20 mm / Strong southwest winds / Alpine temperature 0 C / Freezing level 2000 m
Avalanche Summary
Many natural and explosive-controlled avalanches were observed on Wednesday and Thursday. Loose wet avalanches were generally size 1 and 2 and most often observed at treeline and alpine elevations and on all aspects. The slab avalanches were generally size 2-3 and between 1700 and 2700 m on all aspects. The natural avalanche activity should decrease into Friday with the cooler temperatures and decreased precipitation.
Snowpack Summary
The wet weather on Thursday dropped around 30 mm of rain onto the snowpack, likely to mountain top for most of the region. Rain switched to snow Thursday afternoon, which may not bond well to the underlying wet snow. Deeper in the snowpack, there are two weak layers, including a layer down around 50 to 80 cm at treeline elevations as well as a crust with weak facets around it down around 80 to 130 cm. The layer down 50 to 80 cm may be more prominent in the northern area of the forecast region and the crust may be widespread across the forecast region. Both layers may not be as prominent below treeline, particularly below 1500 m. There is much uncertainty with the spatial variation of these layers, largely because of limited data in the forecast region.
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.