Recent storm snow combined with significant warming and solar radiation are driving the avalanche hazard, especially by the afternoon.
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Springtime cornices are large and unpredictable. The sunshine can pack a punch and lead to cornice failures. Give them a wide berth when travelling at ridge crest and avoid overhead exposure.
60-80 cm of recent storm snow sits above a crust at treeline and above. Warming and solar radiation will likely consolidate the new snow into a reactive slab, producing large avalanches. Avalanches may start as dry slabs in the alpine but entrain wet snow and run into below treeline elevations.
The warm-up last week produced some deeper and bigger avalanches that ran to the valley bottom. These failed on a December rain crust that exists a metre off the ground. There is a lot of uncertainty with this interface and whether it will wake up or not over the next two days.
Sun and warm temperatures will weaken the snow surface on sun-exposed slopes, creating wet avalanches. Watch for wet and heavy snow and be aware of overhead exposure to big sunny slopes.
Thursday: A mix of sun, clouds, and very WARM. Freezing levels rise to 2900 m by the afternoon. Alpine temperatures +3C and ridgetop wind moderate to strong from the southwest.
Friday: No overnight refreeze and WARM. The freezing level holds at 2900 m but should start to drop by 4 pm. Cloudy with a mix of rain and snow up to 15 mm. Ridgetop winds strong from the southwest.
Saturday: Cloudy and cold with new snow up to 10 cm. Freezing levels drop to 700 m and ridgetop winds switch to the northwest.
On Tuesday, numerous natural, explosive, and rider-triggered avalanches were reported up to size 3.5. Most of these avalanches failed within the recent storm snow, however, some of the larger ones were reported as a persistent slabs that failed on a buried crust.
Continued warm temperatures solar radiation will likely trigger a natural avalanche cycle on Thursday and Friday.
By Thursday afternoon, wet snow surfaces may exist to mountain top on most aspects leaving only high North facing terrain with some dry snow.
20 to 40 cm of recent storm snow has buried multiple crusts in the upper snowpack. Moderate to strong west/ southwest has redistributed some new storm snow in exposed high elevation terrain forming wind slabs and developing large cornices.
The new snow brings 60-80 cm above the crust from late March. This crust is present on all aspects up to an elevation of 2500 m.
The early-December rain crust is approximately a metre off the ground. Large slab avalanches failed on this interface last week following a rain and warming event. This layer may be active over the next two days of warm weather.
