Sunday March 17, 2019

Tuesday March 19, 2019
Monday March 18, 2019
Sunday March 17, 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 major warming trend and the persistent weak layers in the snowpack, we are cautioning people to select Simple Terrain. Simple Terrain implies lower angled slopes generally 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 tree bombs as treeline vegetation will continue to shed snow from their limbs over the next few days.

Avalanche Summary

There is a Special Public Avalanche Warning (SPAW) on Vancouver Island due to the sustained warming trend taking place for the next several days here on Vancouver Island. Snowmobile Triggered Loose Wet Avalanche (size 1.5+) was triggered today March 18th in the Gold River area in a cut block.

Avalanche Problems

Cornice Fall

Above mountain top freezing levels will further weaken cornices that developed over the past week from extreme winds and new snow. Be very cautious in terms of your route selection and do not travel below slopes with overhead exposure from cornices.

Wet Slab

Recent 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 or wet snow will be further aggravated by rising warm temperatures.

Loose Wet

The increase in temperature will add increased stress to the upper snowpack. Expect isothermal type conditions below treeline as the upper snow pack has undergone a major temperature shift from cold to warm and snowfall to rainfall. Slopes steeper than 30 degrees are now exposed to a major warming trend over the next few days and will become very likely areas to trigger avalanches.

Deep Persistent Slab

Two persistent weak layers (PWL’s) down 40-60cm and 60-80cm (depending on aspect and elevation) will become likely to trigger on unsupported terrain steeper than 30 degrees. The upper snowpack will begin 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

Two persistent weak layers (PWL’s) down 40-60cm and 60-80cm (depending on aspect and elevation) will become likely to trigger on unsupported terrain steeper than 30 degrees. The upper snowpack will begin 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

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) will begin to melt snow at the snowpack surface which will subsequently overburden these deeper PWL’s. The heating and melting process increases the load and weight onto these PWL’s and will increase the likelihood of human triggering. For these reasons, we may initiate a Special Public Avalanche Warning in conjunction with Avalanche Canada for this upcoming week.

The avalanche hazard below treeline will be less of a hazard due to the fact that this elevation band has been exposed to warmer temperatures for a longer period of time and therefore the upcoming warming trend will not have as dramatic an effect, as the BTL snowpack is already undergoing a melting process. That being said, people are likely to initiate avalanches on steep unsupported terrain below treeline.

Snowpack Details

SurfaceHeavy and moisture laden snow, less heat affected in Alpine (by Monday all elevation bands will undergo major warm up!
UpperTreeline upper snowpack is warm wet and limited chances to refreeze overnight
MidTwo major Persistent Weak Layers (Surface Hoar 40-60cm down and Facet layer 60-80cm down
LowerWell Settled

Past Weather

Air Temperatures have gradually been increasing over the past week with temperatures dropping below zero overnight. Precipitation has come in the form of rain below 1,100M of elevation and snow above.

Weather Forecast

If forecast models are accurate, air temperatures will rise well above mountain top (10,000ft) for the next several days. No cooling below zero degrees is expected until later in the week once temperatures start to drop again.

Sunday - 1mm of rain, light winds from the South shifting to North, temps +2 to +6 , freezing level 2,700M.

Monday- no precipitation expected, moderate winds from ESE, temps +7 to +9, freezing level 3,200 M.

Tuesday - no precipitation expected, strong winds from ESE, . temps +8 to +6, Freezing level 2,700M

Posted on Sunday March 17, 2019 by Ryan Shelly

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