Avalanche Forecast

Unsettled conditions are expected on Monday as a weather system off the north coast moves southward resulting in a shifting wind direction and lower freezing levels for the region. The system is expected to reach the region Monday evening bringing light snowfall for Tuesday. 

Sunday Night: Partly cloudy, light to moderate NW wind, freezing levels around 2200 m.

Monday: A mix of sun and cloud, light to moderate NW wind, freezing levels around 1500 m.

Monday night and Tuesday: Light snowfall 5-10 cm, light to moderate NW wind, freezing levels around 800 m.

Wednesday: Sunny, moderate to strong NE wind, freezing levels around 500 m.

On Saturday, a natural size 2.5 persistent slab was reported on a northeast aspect in the alpine. This avalanche propagated 300 m wide and is assumed to have failed on the February crust/facet layer. A variety of natural loose wet avalanches up to size 2 were also reported. One of these triggered a slab which failed down 50-80 cm, presumably on the crust/facet layer. Some natural cornice failures were also reported which had occurred sometime in the past three days and had triggered slabs on the slopes below. 

On Friday, three size 1.5-2 persistent slab avalanches were human triggered and failed on a weak crust/facet layer buried late-February. This MIN report describes one of them which was on a west aspect at around 1950 m and released down 50 cm. Another was on an east aspect at around 1800 m elevation and the third was on a steep convex feature at treeline. Some human-triggered loose dry avalanches were observed on north aspects and some solar-triggered loose wet avalanches were observed on steep sun-exposed slopes. 

On Thursday, several persistent slab avalanches were reported up to size 2.5. Four of these were natural and the rest were human-triggered including one which was remotely triggered. Two of the naturals were on south aspects which were triggered by loose wet avalanches stepping down. Most of the rest of the activity was on northerly aspects. The majority of the activity appears to have occurred between 1600 and 2000 m elevation. Slab thickness was typically 30-70 cm and the failure plane was a combination of the mid-February and late-February weak layers which may be acting as more of a single thick weak layer. 

A surface melt-freeze crust is now expected on all aspects to at least 2000 m and on sun-exposed slopes into the alpine. Dry surface snow is still expected on high elevation shaded aspects, and recent periods of moderate northerly wind may have redistributed this old storm snow and formed wind slabs in exposed high elevation terrain. 

A weak crust/facet layer which was buried late-February is typically down 30-60 cm and has been responsible for numerous human-triggered avalanches between Wednesday and Friday. The interface has been most reactive on shaded aspects between 1600 and 2000 m. There were also some avalanches on southerly aspects earlier in the week but with each subsequent day of melt-freeze conditions, the persistent problem has become unlikely on sun-exposed slopes. 

Cornices had been reported to have grown large during last week's storm, primarily on north and east aspects, and there were a few cornice failures over the weekend. Cornices are expected to be less of a concern on Monday as freezing levels drop and there is less sun in the forecast. 

• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.