Avalanche Forecast

Archived

Dec 7th, 2019–Dec 8th, 2019

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Rockies.

If we get less than 15 cm Saturday night into Sunday; treat the alpine as CONSIDERABLE. Clear skies and pow are rad, but we all need to keep the terrain choices conservative Sunday, it's a long winter and we're just getting to know our young snowpack.

Confidence

Low - Forecast snowfall amounts are uncertain. Uncertainty is due to the limited number of field observations.

Weather Forecast

The weather pattern is setting up to offer the South Rockies a decent amount of storm snow Saturday night into Sunday morning before an Arctic Ridge takes over for the work week.

SATURDAY NIGHT: Freezing level around 1200 m lowering to valley bottom by dawn, moderate to strong west/southwest wind, 5 to 20 cm of snow expected.

SUNDAY: Overcast at dawn, clearing by mid-morning, light to moderate northwest wind, a few cm of snow possible.

MONDAY: Scattered cloud cover, freezing level at valley bottom, light west/northwest wind, no significant precipitation expected.

TUESDAY: Scattered cloud cover, freezing level at valley bottom, light southwest wind at valley bottom, potentially strong northwest wind at ridgetop, no significant precipitation expected.

Avalanche Summary

Recent avalanche observations are limited. A couple of small wind slabs triggered by explosives were reported over the past week.

Large explosives in early season control work have triggered several large avalanches stepping down to deeper weak layers. While human triggering these larger avalanches remains unlikely in the short term, these results are indicative of persistent weak layers lingering in the snowpack that may become more reactive with additional loading.

Snowpack Summary

The 2 to 5 cm of snow that fell Friday Night brings the storm total to 10 to 15 cm from this week's scattered flurries.

Crust layers from November and October can still be found deeper in the snowpack (check out this MIN report from Mear Lake). As the load on these weak layers increases with new snow and wind, these persistent weak layers could become more reactive.

Snowpack depths are highly variable this early in the season with amounts ranging between 50-100 cm at higher elevations and tapering rapidly below treeline.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.