Avalanche Forecast

Issued: Mar 10th, 2017 4:40PM

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

cgarritty, Avalanche Canada

South Coast.

Persistent weak layers are not typical on the South Coast. Backcountry users in the region need to keep in mind the possibility for storm slab avalanches to 'step down' well beyond the depth of new snow.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Saturday: Periods of snow and rain with 15-30 cm accumulating at higher elevations. Strong south winds, gusting to extreme. Freezing level to 1500 metres with alpine temperatures around 0. Sunday: Periods of snow and rain with 25-30 cm accumulating at higher elevations, mostly in the afternoon. Moderate to strong southwest winds. Freezing level to 1500 metres with alpine temperatures around 0. Monday: Approximately 10-15mm of rain over the day. Moderate to strong southwest winds. Freezing level to 1800 metres with alpine temperatures around +2.

Avalanche Summary

No new avalanches have been reported, but it should be noted that stormy weather has been discouraging backcountry travel and obscuring visibility into alpine terrain.On Wednesday, explosives triggered two size 1 storm slabs which released down 10-25 cm. These were described as having minimal propagation and minimal entrainment.Looking forward, expect a drastic change in avalanche hazards as you transition between elevation bands. Loose wet avalanche hazards will dominate where rain and wet snow accumulate, while thick, reactive storm slabs can be expected at higher elevations. This increases the need for awareness of overhead hazards. To complicate matters, large persistent slab avalanches may still be possible in isolated areas, and this potential increases while precipitation (especially rain) loads the snowpack.

Snowpack Summary

Another 15-20 cm of new snow fell in the North Shore mountains over Thursday night, bringing the typical storm accumulation in the past week to 130-200 cm. Our most recent winds have been from the south, but previous winds were more variable and formed wind slabs on all aspects below our most recent new snow accumulations. Mid storm layers in the upper snowpack have recently produced moderate, resistant results in snowpack tests. Below the recent storm snow, you'll find the late-February interface. This layer is composed of a sun crust on southerly aspects and surface hoar on shaded aspects. Recent snowpack tests of this layer have produced variable results with occasional sudden fracture character. With this in mind, conservative choices are still recommended until there is higher confidence in this layer becoming unreactive. We could still be in a low probability, high consequence scenario where very large avalanches remain possible in isolated areas. Substantial snowfall and warming in the forecast are two factors that may promote increasing reactivity at this interface over the weekend. the Below this interface, the mid and lower snowpack appear to be well settled and strong.

Problems

Storm Slabs

Another 15-20 cm of new snow is likely to accumulate at higher elevations by Saturday afternoon. Warm temperatures and strong to extreme winds will continue to promote the formation of touchy storm slabs that will be primed for human triggering.

Use extra caution on slopes if the snow is moist or wet.Minimize overhead exposure during periods of heavy loading from new snow, wind.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

Storm snow from the past week sits over a buried persistent weak layer and very large avalanches may still be possible in isolated terrain. The likelihood of a persistent slab release increases while new snow and rain add load to the snowpack.

Be aware of the potential for very large avalanches due to deeply buried weak layers.If triggered, storm slabs may step down to deeper layers resulting in very large avalanches.Minimize overhead exposure during periods of heavy loading from new snow, rain, and wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Wet snow and rain at lower elevations will allow surface snow to sluff easily from steep terrain. These sluffs may entrain significant mass and become a serious hazard, especially around terrain traps like cliffs or above terrain depressions.

Use extra caution on slopes if the snow is moist or wet.Be cautious of sluffing in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Mar 11th, 2017 2:00PM