South Rockies Avalanche Forecast

Mar 5th, 2020 4:00PM

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

We're not expecting much overnight re-freeze Thursday night which may allow for increasingly sensitive cornices Friday. Watch for changing conditions late in the afternoon, a bit of precipitation and wind are expected before sunset.

Summary

Confidence

Low - Uncertainty is due to the timing of the incoming weather system. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Dramatic weather through the forecast period.

THURSDAY NIGHT: Freezing level around 2100 m, moderate to strong southwest wind, no precipitation expected.

FRIDAY: Scattered cloud cover in the early morning building to overcast in the afternoon, freezing level around 1900 m, moderate to strong southwest wind picking up in the late afternoon, 5 to 15 mm of precipitation expected in the late afternoon/early evening, falling as rain at lower elevation and snow up high.

SATURDAY: Overcast, freezing level returning to valley bottom just before dawn and then staying near valley bottom all day, light variable winds at lower elevations, strong southwest wind in the alpine, 10 to 25 cm of snow possible.

SUNDAY: Broken cloud cover, freezing level near valley bottom, light to moderate southwest wind, no significant precipitation expected.

Avalanche Summary

No avalanches have been reported since last week, but there have been limited field observations. A few natural size 2 wind slabs have been reported on north and east aspects in the neighbouring Kananaskis region.

A very large (size 3) deep persistent slab avalanche was observed north of Sparwood last Friday on a steep southeast facing alpine slope. This follows a pattern of sporadic deep slab releases in the upper Elk Valley including this natural avalanche from Feb 11 and this sled triggered avalanche from Feb 9. These types of large avalanches will be most likely during periods of heavy loading or intense warming.

Snowpack Summary

A storm passing through Tuesday night delivered 5-10 cm to the region with closer to 15-20 cm along the northern parts of the region near Kananaskis Country. This snow was accompanied by strong to extreme wind from the west and formed fresh wind slabs in exposed terrain. A crust can be found near the surface up to 2300 m on solar aspects and up to 1700 m on all other aspects.

A thick rain crust sits 40-80 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17. The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Choose gentle slopes without steep terrain above.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Avoid exposure to overhead hazards when solar radiation is strong.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Recent snow has been blown around by strong to extreme wind from the west over the past few days. Watch for wind slabs in the immediate lee of ridges. 

Aspects:

North, North East, East, South East, South.

Elevations:

Alpine, Treeline.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

2.5 - 3.5

Weak snow at the bottom of the snowpack hasn't gone away unfortunately, and will continue to be a concern on big terrain features. Evidence of deep persistent slab avalanches has been focused in the Sparwood-Elkford area over the past month. Human triggering is most likely around steep rocky terrain features, or anywhere the snowpack is thin and weak. Natural triggering is possible on slopes below cornices and on slopes that warm up in the heat of the day. 

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Mar 6th, 2020 5:00PM