Avalanche Forecast

Issued: Jan 10th, 2018 4:46PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs and Persistent Slabs.

mconlan, Avalanche Canada

Lizard-Flathead.

Very dangerous avalanche conditions. Travel in avalanche terrain is not recommend.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

THURSDAY: Cloudy with snowfall, accumulation 15 to 25 cm, light to moderate southwesterly winds, alpine temperature near -10 C, freezing level below valley bottom.FRIDAY: Mostly cloudy with early morning snowfall, light to moderate westerly winds, alpine temperature near -9 C, freezing level near 1000 m.SATURDAY: Mostly cloudy with intermittent snowfall, moderate to strong westerly winds, alpine temperature near -5 C, freezing level near 1200 m with possible inversion conditions.

Avalanche Summary

A widespread natural avalanche cycle was observed on Tuesday and Wednesday. Numerous large avalanches (size 3 to 3.5) were triggered in the alpine and ran to near the valley floor and numerous size 2 avalanches started at and below treeline. Operators also reported numerous large human, vehicle, and remote-triggered avalanches. Some of these avalanches ran on relatively shallow slope angles (around 30 degrees) and in fairly dense trees. Expect continuing avalanche activity on Thursday. The natural cycle will probably slow a little as temperatures cool, but as long as it is snowing and blowing, avalanche activity will likely continue.

Snowpack Summary

The snowpack reached its tipping point on Tuesday and Wednesday as warming and precipitation combined to overload persistent weak layers in the snowpack and create a large natural avalanche cycle. More snowfall on Thursday will continue this dangerous trend.Over 100 cm has fallen in the past few days. The snow fell relatively warm with moderate winds, which has formed storm slabs. Deeper in the snowpack, an unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations. Below, a rain crust that developed late-November with associated sugary facets are also being stressed. Snowpack test results show sudden fracture characters and high propagation potential for both of these buried layers, indicating that they can be triggered and could propagate into large, destructive avalanches. This has been the case, as shown in the Avalanche Summary.

Problems

Storm Slabs

Many avalanches have been naturally and human-triggered in the recent 100+ cm of snow. If triggered, storm slabs could step down to deeper persistent weak layers.

Avoid exposure to overhead avalanche terrain. Large avalanches may reach the end of run out zones.Avoid exposure to terrain traps where the consequence of any avalanche could be serious.Use caution when entering lee areas. Recent wind loading may have created wind slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 3

Persistent Slabs

Skier and machine traffic have triggered large avalanches on buried weak layers, even in relatively dense trees and shallow slope angles. These weak layers are touchy and can produce large, destructive avalanches that run far.

Travel in avalanche terrain is not recommended with current conditions.Minimize overhead exposure during periods of heavy loading from new snow and wind-transported snow.Use caution above cliffs and terrain traps where avalanches may have severe consequences.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 4

Valid until: Jan 11th, 2018 2:00PM