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Avalanche Forecast

Archived

Nov 22nd, 2019–Nov 23rd, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

New slab development begins with incoming snow and wind. Watch for changing conditions, especially in windy areas where 15 cm of snow could accumulate by the end of the day. Deeper layers remain a concern.

Confidence

Low - Uncertainty is due to the timing of the incoming weather system. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Friday night: Increasing clouds, freezing level around 1200 m, light southwesterly winds, and a trace of precipitation.

Saturday: Overcast, freezing level around 1200 m, moderate southwesterly winds, and 5-15 cm of snow.

Saturday night: Another 5-15 cm of snow possible with southwesterly winds. Higher precipitation amounts will fall in the northern part of the region.

Sunday: Continuing flurries, winds shifting to the west/northwest, and the freezing level dropping from 1200 m.

Avalanche Summary

The last reports of avalanches came in on Tuesday, November 19th. 

Snowpack Summary

The incoming storm brings a change and a test for our snowpack. After a week of clear skies, the existing snow surfaces may not bond well with the new snow. As the new snow accumulates, it could develop into a reactive slab, especially in drifted areas near and above tree line. 

The incoming storm presents an opportunity to observe how the problem weak layers (late October crusts) buried 40-70 cm deep in the snowpack react to a new load. 

The average snowpack depth at tree line is approximately 100 cm.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.