The possibility exists for a large avalanche to run on deep weak layers due to the impact of warm temperatures and solar activity.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
The weather pattern is currently dominated by a strong upper ridge of high pressure giving dry conditions.Saturday: Slightly cooler air is expected to move in to this area through the day. Alpine temperatures will become considerably cooler, although still warm in the range of 0 to 5C. Winds are expected to pick up becoming moderate SW by the end of the day.Sunday: A cooler day with alpine temperatures around 0C. Winds should become light. Monday: Alpine temperatures once again climbing to +5 or possibly higher. Light winds.
Avalanche Summary
On Thursday, a natural avalanche occurred on the SE face of Mt. Rohr, size 2.5, running to mid runout on basal facets. On Wednesday, explosive control in the North Cascades produced a couple size 2.5 on N and NE aspects. In the same area, there was also some loose wet avalanches below treeline up to size 1. In the Northern part of the region, there was also report of remotely triggering a couple size 2 avalanches which would have run on basal facets in the alpine on NE aspects.
Snowpack Summary
Very warm alpine temperatures have created a moist snow surface. Previous winds have scoured windward slopes and sculpted sastrugi in exposed areas. Initially, the bond below the most recent storm snow was weak. However, settlement due to the warm temperatures appears to have settled the upper snowpack and it has appeared to have gained strength.There are two lower layers of note near the base of the snowpack. A facet/crust combo from late November (down approximately 100-120 cm) is still giving "sudden" results in compression tests and exists at treeline and alpine elevations. Facets and depth hoar likely still exist at the base of the snowpack, especially in areas where the snowpack was particularly shallow early on in the season. The most likely places you would find this problem is in the alpine in shallow rocky areas, and it has been most widely reported from the Duffey Lake and Chilcotin areas.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.