Substantial warming and sun exposure this week are expected to wake-up deeply buried weaknesses within the snowpack. Conservative terrain selection is critical and it is best to avoid avalanche terrain during the heat of the day.
Summary
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
A blocking ridge of high pressure is the dominant feature for the week. Dry and clear conditions are expected for Tuesday through Thursday. Freezing levels are expected to climb to around 2700m on Tuesday afternoon and should be above 3000m on both Wednesday and Thursday afternoon, with cooling during the overnight periods. Strong northwest winds are expected on Tuesday in exposed terrain. Light to moderate northerly winds are forecast for Wednesday and light northwesterly winds on Thursday.
Avalanche Summary
On Sunday, a skier triggered a size 1.5 persistent slab avalanche on a steep roll on a northeast aspect at 1400m elevation. The slab was typically 40cm thick and released on a layer of surface hoar that was buried on March 23. A ski cut at the top of a steep north facing chute at 1100m elevation triggered a size 2 persistent slab which failed on a crust. A helicopter remotely triggered a size 1.5 wind slab from 150m away on an east aspect. Natural cornice releases were reported to have triggered slabs up to size 3.5 which were stepping down to ground. Point releases were reported up to size 2 and glide cracks up to size 2.5. Explosives also triggered a couple size 2 wind slabs on north aspects around 1500m. All of this activity was reported from north of Stewart. On Tuesday, substantial warming and sun are expected to result in natural cornice releases and may also result in deep persistent slab releases. Lingering wind slabs also remain a concern.
Snowpack Summary
10-30cm of recent storm snow has accumulated in sheltered areas at higher elevations. In exposed terrain, southerly winds have formed soft slabs in leeward features. A weak crust/surface hoar layer which was buried last week is down 30-40cm in the north of the region. A widespread crust/facet layer buried in early February and a lingering surface hoar layer from January can now be found down over a metre. These layers still have the potential to produce large avalanches, especially with a large trigger such as a cornice fall. Extra caution is required during periods of substantial warming and intense solar radiation, as these layers have the biggest potential to wake up. At treeline and below, spring melt-freeze conditions are already being reported. These conditions are expected to extend well into the alpine this week with the forecast warming and sun.
rbuhler,
Avalanche Canada
