North Rockies Avalanche Forecast

Mar 9th, 2020 5:00PM

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

New snow forecast for Tuesday is expected to arrive with moderate to strong west and southwest wind. This will make wind slabs at upper elevations the main concern.

Summary

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

MONDAY Night: Mainly cloudy with scattered flurries, accumulation 5 cm. Moderate to strong west wind. Alpine temperature around -10.

TUESDAY: Cloudy with flurries, accumulation 5-15 cm. Strong southwest wind. Alpine temperature around -7. Freezing level 1000 m.

WEDNESDAY: Cloudy with sunny periods and isolated flurries. Moderate to strong west wind. Alpine temperature around -9. Freezing level 600 m.

THURSDAY: Cloudy with sunny periods. Moderate to northwest wind. Alpine temperature around -11. Freezing level at valley bottom.

Avalanche Summary

There was a report of rider triggered size 2 avalanche in the Pine Pass area on Saturday at tree line on a northeast aspect. The fracture was approximately 50-70 cm deep. There was also a report of a snowmobile triggered avalanche in the Mackenzie area on the same day. There are not a lot details regarding these two events, but they were possibly triggered in wind loaded areas. Additionally the fracture depths correspond to the approximate depth of a weak layer of surface hoar that was buried near the beginning of February. This surface hoar may have become more reactive due to the snow stiffening above with wind loading.

Snowpack Summary

10-20 cm new snow is forecast to arrive Monday night and through Tuesday. This will add to the equivalent amount from last week. Strong west winds are expected to redistribute the new snow into lee terrain at upper elevations.

The recent snow all sits on either old wind affected snow, rain crust below 1200 m or sun crusts on south and west facing slopes.

The lower snowpack is strong and well-bonded in many parts of the region. However, given the large extent of the region it remains important to understand snowpack conditions in your local riding area. 

The Pine Pass and MacKenzie areas have a weak layer of surface hoar roughly 100 cm below the surface that was a problem around treeline elevations in mid-February, but appears have gained strength since then.

The eastern slopes of the Rockies have many shallow rocky slopes that could harbour weak basal facets.

Cornices have grown large and should be given wide berth, especially if you're travelling on ridge lines.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs are most reactive during their formation.
  • Watch for avalanche hazard to increase throughout the day.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely-Very Likely

Expected Size

1 - 2

10-20 cm of new snow is forecast to arrive Monday night and through the day Tuesday along with moderate to strong west and southwest winds. Expect wind slabs to develop in the lee of terrain features. Avalanche danger will gradually increase through the day. In the Pine Pass and Mackenzie areas, these wind slabs are possibly adding additional load to a weak layer of surface hoar that may be found at the treeline elevation band.

Aspects:

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

Elevations:

Alpine, Treeline.

Valid until: Mar 11th, 2020 2:00PM