Recent storm snow combined with significant warming and solar radiation are driving the avalanche hazard, especially by the afternoon.
Check out the Forecaster Blog for additional details.
Springtime cornices are large and unpredictable. The sunshine and warming 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 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, especially on sun-exposed slopes, creating wet avalanches.
Thursday: A mix of sun, clouds, and very WARM. Freezing levels rise to 3000 m by the afternoon. Alpine temperatures +5C and ridgetop wind moderate to strong from the southwest.
Friday: No overnight refreeze and WARM. The freezing level holds at 3000 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 1000 m and ridgetop winds switch to the northwest.
On Tuesday, a natural avalanche cycle was noted up to size 2, mostly storm slabs and one persistent slab. A couple of skier remotely (from a distance away) triggered slabs were seen up to size 1.5 and dry loose avalanches up to size 1.5.
On Monday, evidence of a widespread natural avalanche cycle up to size 3 but the average storm/ wind slabs were reported to size 2 and failed in the recent storm snow. Some larger avalanches may have failed on the end of March melt-freeze crust. Most notable was a natural size 3.5 storm slab that started at 2600 m and ran to the valley bottom.
Warm temperatures and solar radiation will likely trigger a natural avalanche cycle on Thursday and Friday
By the afternoon on Thursday, wet snow surfaces may exist to mountain top on most aspects leaving only high North facing terrain with some dry snow.
15 to 30 cm of storm snow has blanketed the region and buried multiple crusts in the upper snowpack. Moderate to strong west/ southwest wind has redistributed some of the new storm snow in exposed high elevation terrain forming wind slabs and developing large cornices.
The new snow brings 60-80 cm above will a crust from late March. This crust is present on all aspects up to an elevation of 2600 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 weathern.
