Avalanche Forecast

Issued: Feb 7th, 2019 5:01PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Persistent Slabs, Wind Slabs and Deep Persistent Slabs.

cgarritty, Avalanche Canada

South Rockies.

Check out the Forecasters' Blog here for insight on the persistent slab problem emerging in the South Rockies.A Special Public Avalanche Warning is in effect in this region.

Summary

Confidence

High -

Weather Forecast

Thursday night: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southwest or west winds.Friday: Mainly cloudy with continuing isolated flurries bringing a trace to 3 cm of new snow, continuing overnight. Light east winds. Alpine high temperatures around -20 and falling over the day.Saturday: Mainly cloudy with continuing isolated flurries and a trace of new snow. New snow totals around 4-8 cm. Light northeast winds. Alpine high temperatures around -29.Sunday: Cloudy with sunny periods. Light northeast winds. Alpine high temperatures around -21.

Avalanche Summary

A social media post from the Marten area of Elk Valley 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.

Problems

Persistent Slabs

A weak layer of surface hoar is now buried 35-45 cm deep. This layer has been regularly producing large avalanches in adjacent regions where it is only slightly deeper. 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.

Likelihood

Possible

Expected Size

1.5 - 2.5

Wind Slabs

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.

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.

Likelihood

Possible

Expected Size

1 - 2

Deep Persistent Slabs

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.Watch for signs of instability such as whumpfing, cracking, or recent avalanches.Avoid steep, rocky terrain and shallow snowpack areas where triggering deep layers is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Valid until: Feb 8th, 2019 2:00PM