Wednesday March 20, 2019

Friday March 22, 2019
Thursday March 21, 2019
Wednesday March 20, 2019
Confidence: High - Weather models in agreement, sufficient field weather and snowpack observations

Main Concerns

Cornice Fall, Wet Slab, Loose Wet, Deep Persistent Slab, Persistent Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Due to the rapid warming of the upper snowpack and the deeper persistent weak layers in the snowpack, we are cautioning people to select Simple Terrain. Simple terrain implies lower angled slopes under 30 degrees where multiple options exist to eliminate your exposure to avalanche terrain. Dense forests would be a great spot to recreate for now except keep an eye up for cornices overhead as these generally unstable areas are at an all time hazard and should be avoided.

Avalanche Summary

On Monday, there was a reported snowmobile triggered wet slide (size 1.5+) in the Gold River area on a cutblock slope steeper than 30 degrees. The rider caught in the avalanche was able to stay on the snowmobile and avoid getting swept down slope in the wet avalanche. No propagation but due to major warming of upper snowpack the wet avalanche entrained snow below it until hitting a road.

Currently the avalanche hazard rating is such that natural avalanches are likely and humans are very likely to trigger avalanches. For these reasons, we are maintaining the Special Public Avalanche Warning until further notice and urging people to recreate in areas under 30 degrees of slope angle.

Avalanche Problems

Cornice Fall

Above mountain top freezing levels will further weaken cornices. Friday’s rain could also exacerbate and further weaken cornices. Be very cautious in terms of your route selection and do not travel above, adjacent to or below slopes with exposure to cornices.

Wet Slab

Snowfall and wind events from this past week may provide appropriate bed surfaces for initiating avalanches due to major heating trend over the next few days. Slopes steeper than 30 degrees that received rainfall (Friday) or are wet from high air temperatures will be further aggravated by rising warm temperatures.

Loose Wet

The increase in temperature will add increased stress to the upper snowpack. Expect isothermal (melting and bottomless) type conditions at all elevation bands over the next couple days as the upper snow pack has undergone a major rapid warming phase. Slopes steeper than 30 degrees are now likely to experience a natural avalanche cycle. In addition to rapid warming, precipitation in the form of rain is expected Friday which will also overload the unstable upper snowpack.

Deep Persistent Slab

It depends on aspect (exposure to wind and sun), however there are two persistent weak layers (PWL’s) down 40-60cm and 60-80cm (depending on aspect and elevation). These PWL’s are likely to trigger on unsupported terrain steeper than 30 degrees. The upper snowpack will continue a sustained melting process for the next few days which will bring additional load and stress to these PWL’s, further increasing the likelihood of triggering.

Persistent Slab

It depends on aspect (exposure to wind and sun), however there are two persistent weak layers (PWL’s) down 40-60cm and 60-80cm (depending on aspect and elevation). These PWL’s are likely to trigger on unsupported terrain steeper than 30 degrees. The upper snowpack will continue a sustained melting process for the next few days which will bring additional load and stress to these PWL’s, further increasing the likelihood of triggering.

Snowpack Summary

The upper snowpack is undergoing a rapid melting process, with zero opportunity to refreeze overnight, we expect the upper snowpack to continue to provide wet avalanches until a major cooling trend can take effect.

There are two main persistent weak layers (PWL’s) in the upper 60 - 80cm of the Vancouver Island snowpack. The first PWL is surface hoar and can be found down anywhere from 40 - 60 cm down depending on aspect and elevation. The surface hoar hazard is widespread however it may not be present on certain specific solar aspects. The second PWL is a facet - crust interface and can be found down 60-80cm from the surface of the snow depending on aspect. Both of these layers are providing results on testing and we foresee the ability of initiation of these layers to increase in likelihood given the very warm air temperatures for the next several days. Near double digit air temperature in the Alpine (which we have not seen since January) have been melting the upper layers of the snowpack. The rapid warming of the snowpack will subsequently overburden these deeper PWL’s. The heating process increases the load and weight onto these PWL’s and will increase the likelihood of human triggering. For these reasons, we have initiated a Special Public Avalanche Warning in conjunction with Avalanche Canada for this week.

Snowpack Details

Surface30+cm of highly unstable, melting snow (isothermal snow). Week old storm and wind slab layers
Upper2 persistent weak layers are now overloaded with additional weight from melting snow above
MidVariety of melt freeze crusts from January freeze thaw cycle
LowerWell Settled

Past Weather

Double digit warm temperatures at Treeline Elevation. No new precipitation but the rapid warming is the reasoning for the Special Public Avalanche Warning.

Weather Forecast

Air temperatures will remain at near double digit temps at treeline on Wednesday. On Thursday, a cooling trend begins but temps will remain above zero. On Friday, a low of zero degrees is in the forecast however rain is also expected on Friday March 22 below treeline, which is why we will maintain a “considerable” danger rating for the treeline elevation band.

Wednesday - No precipitation, Moderate to Strong Winds from the ESE at 1500M of Elevation, Temps +11 to + 9, Freezing Level 3,000M

Thursday- No precipitation, Moderate Winds from SE, Temps +7 to +2, Freezing Level 2,500 M.

Friday - 3MM of Rain, Moderate Winds from SE, Temps +2 to 0, Freezing Level 1,300M

Posted on Tuesday March 19, 2019 by Ryan Shelly

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