Avalanche Forecast

Issued: Feb 28th, 2014 8:20AM

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

bcorrigan, Avalanche Canada

Purcells.

Although the frequency of natural avalanches has gone down recently, the possibility of triggering a large, destructive avalanche is still very real. See the Forecasters Blog for more insight into this tricky situation.

Summary

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

The ridge of high pressure continues to dominate the forecast. Dry cold arctic air has moved into the region and will remain for the next few days. By the end of the weekend we should see more seasonal temperatures with some precipitation. For a more in-depth look at upcoming weather conditions, check out the: WEATHER OUTLOOK Friday night: Clear with a few clouds, freezing level at valley bottom, no precipitation in the forecast, ridge top winds from the north to 20 Km/h.Saturday: Sunny, freezing level at valley bottom, ridge top winds from the southeast around 15 Km/h.Sunday: Sunny, with a few clouds, freezing level at valley bottom, ridge top winds light to 15 Km/h from the SE. Possibility of an alpine temperature inversionMonday: Cloudy with isolated flurries, freezing level at valley bottom, ridge top winds from the south 10-20 Km/h.

Avalanche Summary

Natural avalanches are still occurring up to size 2.5 in the forecast area, and as temperatures warm up may increase in frequency. Cornices failures may also occur with the warming temperatures and will certainly add to the hazard.Conditions are ideal for rider triggering right now. We have received numerous reports of skier triggered and skier accidental avalanches, many of which have released quite deep in the snowpack. Neighboring areas have reported avalanches that were remotely triggered from a considerable distance.

Snowpack Summary

The storm slab of about 1 metre overlies a persistent weak layer, (surface hoar/facet/crust combo) that was formed during the preceding month of cold dry weather. The storm slab appears to be gaining strength with settlement and warm temperatures but the persistent weak layer beneath it remains widespread at all elevations and aspects. Although this weak layer is not as reactive as it has been, it's still a very real concern. Surface hoar and near surface facetting is occurring on protected/shaded aspects, and solar aspects are moist to quite high elevations during the day with sun crusts forming at night. Winds shifting from south west to north east will signal wind slab development on south east slopes when the arctic outflow arrives from the northeast.Large settlements and whumpfs are still being reported indicating the ability of this weak layer to fail. Remotely triggered avalanches tell us it has the ability to propagate over large distances. Touchy conditions will remain for the near future.

Problems

Persistent Slabs

A dense storm slab now lies over a touchy, persistent weak layer. This weak layer can be triggered remotely (from a distance) and propagate over large areas. In wind-loaded areas the slab may be up to 1.5m thick. Use conservative terrain choices.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Use very conservative route selection, stick to simple well supported terrain that is low consequence and free of overhead hazard.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Previous storm winds have created wind slabs on lee terrain features. The primary wind direction was SW but we're about to get some NE winds. Cornice failure is also a concern and has the potential to trigger large avalanches on the slopes below.

Avoid freshly wind loaded features.>Minimize overhead exposure; avalanches triggered by windloading may reach run out zones.>Travel on ridgetops to avoid wind slabs on slopes below.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Mar 1st, 2014 2:00PM