Avalanche Forecast

Moderate - Uncertainty is due to the limited number of field observations.

  

SATURDAY NIGHT: Snow; 5-10 cm. / Moderate to strong, southwest ridgetop wind / alpine low temperature -9 / Freezing level valley bottom.

SUNDAY: Mostly cloudy / Light, west ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

MONDAY: Mostly cloudy with sunny periods / Light, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

TUESDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

15-25 cm. of new snow since Christmas day has buried yet another weak layer of surface hoar that was widespread at treeline and below. Expect this new snow to become increasingly reactive to human triggers as it settles into a cohesive slab.

There have been numerous recent reports of dry loose avalanches(sluffs) running surprisingly fast and far below treeline.

On Wednesday, there was a report of several size 3 to 4 explosive triggered deep persistent and persistent slab avalanches in the north of the region along the Highway 1 corridor. These ranged from south and east aspects to northeast running from the alpine to the valley floor.

Reports on Tuesday showed a widespread storm slab and persistent slab avalanche cycle in the alpine and at treeline. Avalanches sizes ranged from size 1.5 to 3 on all aspects. Additionally, reports from Tuesday in Rogers Pass indicate several natural and explosives triggered persistent slab avalanches to size 4 running full path from the alpine to the valley floor Monday night. 

15-25 cm. of new snow since Christmas day has buried yet another weak layer of surface hoar that was widespread at treeline and below. Expect this new snow to become increasingly reactive to human triggers as it settles into a cohesive slab.

Lingering wind slabs formed last week may remain reactive on a variety of aspects due to shifting winds.

Just under the new snow, down about one meter below the surface is the mid December surface hoar. This layer had been failing naturally and has been quite sensitive to human triggering throughout the storm cycle. Large avalanches have been running on this interface connecting big terrain features. 

Below that lies the early December persistent weak layer, it's about 80 to 140 cm below the surface. This weak layer is a mixed bag that often presents as surface hoar and facets sitting on top of a supportive crust. This is a nasty weak layer, when avalanches fail on it, they have been large and destructive. Smaller avalanches in motion can step down to this one too.

• Uncertainty is best managed through conservative terrain choices at this time.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.