Avalanche Forecast South Rockies

Friday 8th February 2019

Avalanche Danger Ratings Fri 8th Feb 4:53PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Moderate Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs Deep Persistent Slabs Deep Persistent Slabs

Avalanche Canada Forecaster: cgarritty

Date Issued:

Valid Until:

Check out the AvCan South Rockies blog for advice on managing the persistent slab problem affecting the region. (Link Here)A Special Public Avalanche Warning is in effect in this region.

Confidence

High -

Weather Forecast

Friday night: Mainly cloudy with isolated flurries and a trace to 3 cm of new snow. Moderate to strong northeast winds, with stronger winds at lower elevations.Saturday: Mainly cloudy with isolated flurries and a trace to 3 cm of new snow. Strong northeast winds, strongest at lower elevations, easing over the day. Alpine high temperatures around -25.Sunday: Cloudy with sunny periods. Light variable winds. Alpine high temperatures around -22.Monday: Cloudy with sunny periods. Light southwest winds. Alpine high temperatures around -17.

Avalanche Summary

A social media post from the Marten area of Elk Valley on Thursday describes touchy persistent slab conditions, with lots of smaller slabs releasing over the mid-January surface hoar layer. Check out the post here. Of note is the fact that this area was previously untracked, leaving the mid-January layer undisturbed. This is something to bear in mind as dry conditions persist and the motivation to step out of well-traveled terrain increases. Areas where this layer is undisturbed are far more likely to hold reactive persistent slabs.

Snowpack Summary

Above 1700 m, 25 to 35 cm of recent snow overlies a variety of surfaces, including feathery surface hoar crystals in shaded and sheltered areas, wind-affected snow in exposed terrain, and a melt-freeze crust on southerly aspects. Below 1700 m, expect to find around 5-10 cm of low-density snow on a melt-freeze crust.The mid-January layer of surface hoar or a crust is buried around 35 to 45 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. The melt-freeze crust is found on south aspects at all elevations. This layer is the subject of our Special Public Avalanche Warning. A social media post from the Elk Valley Snow Shepherds from Wednesday does a great job of highlighting the issue. Check the link here.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. The basal snowpack is becoming even weaker under prolonged cold temperatures, especially in thin snowpack areas.

Persistent Slabs Persistent Slabs

Likelihood

Possible

Expected Size

1.5 - 2.5

A weak layer of surface hoar is now buried 35-45 cm deep. This layer is starting to react to human triggering, particularly in areas that haven't seen much traffic. It is best preserved in shaded, sheltered areas between 1600-2200 m.

Increase caution in open features at lower elevations, such as cutblocks, gullies, and cutbanks.Be aware of the potential for large avalanches due to the presence of buried surface hoar.Watch for signs of instability such as whumpfing, or cracking, especially from 1600-2200 m.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Wind Slabs Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Light new snow amounts and continually shifting winds are likely to build thin new wind slabs above a layer of older, increasingly stubborn slabs. The touchiest pockets will likely be adjacent to ridges.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with wind-loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

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Deep Persistent Slabs Deep Persistent Slabs

Likelihood

Possible - Unlikely

Expected Size

2 - 3.5

The bottom of the snowpack consists of weak and sugary faceted snow. The likelihood of triggering this layer may be relatively low, but the consequences remain high. Any deep persistent slab avalanche will be large and destructive.

Avoid steep, rocky terrain and shallow snowpack areas where triggering deep layers is more likely.Use conservative route selection, such as moderate-angled and smooth terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

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