Avalanche Forecast South Rockies

Sunday 10th February 2019

Avalanche Danger Ratings Sun 10th Feb 5:28PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Moderate Persistent Slabs Persistent Slabs Deep Persistent Slabs Deep Persistent Slabs Wind Slabs Wind Slabs

Avalanche Canada Forecaster: cgarritty

Date Issued:

Valid Until:

A trio of avalanche problems is making for tricky terrain selection in the South Rockies. Keep it simple and use low consequence slopes free of overhead hazard to manage your risk exposure.

Confidence

High -

Weather Forecast

Sunday night: Cloudy with clear periods and isolated flurries with a trace of new snow. Light to moderate southwest winds.Monday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds, increasing overnight. Alpine high temperatures around -16. Tuesday: Cloudy with scattered flurries bringing around 5 cm of new snow, continuing overnight. Light southwest winds, increasing to strong in the alpine. Alpine high temperatures around -11.Wednesday: Cloudy with continuing isolated flurries and a trace of new snow, with new snow totals of up to 10 cm. Flurries continuing overnight. Alpine high temperatures around -10.

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. Recent winds continue to redistribute loose snow and develop wind slabs. 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 - 2

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

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Deep Persistent Slabs Deep Persistent Slabs

Likelihood

Possible - Unlikely

Expected Size

2 - 3

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.

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

Aspects: All aspects.

Elevations: All elevations.

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Wind Slabs Wind Slabs

Likelihood

Possible

Expected Size

1 - 1.5

Light new snow amounts and continually shifting winds have been keeping wind slab problems alive at higher elevations. The touchiest pockets will likely be adjacent to ridges and around wind-exposed terrain features.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

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