Avalanche Forecast

Issued: Feb 25th, 2014 8:23AM

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

bcorrigan, Avalanche Canada

Purcells.

Hazards may increase with rising temperatures and solar warming on South aspects. See the forecasters blog for more information on current tricky conditions.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

The arctic ridge of high pressure dominates conditions for the forecast period. Clear and dry conditions are expected for the next three days with a bit of a warming trend. No precipitation in the forecast for the next few days.Tuesday night: Clear, Freezing level at valley bottom, ridge top winds light variableWednesday: Sunny, freezing level around 1000m, possibility of an alpine temperature inversion, ridge top winds light-variable.Thursday: Sunny with cloudy periods, freezing level around 1200m, ridge top winds, light to 25Km/h.Friday: Sunny, freezing level at valley bottom, ridge top winds from the North at 15 Km/h

Avalanche Summary

Natural avalanches are still occurring up to size 3 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 human triggering right now and 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

A cohesive slab with an average thickness of 1.3m sits on a nasty persistent weak layer (surface hoar/facet/crust combo) that was formed during the preceding month of cold, dry weather. This weak layer is widespread at all elevations and aspects, and is creating problems even in previously skied terrain. Large settlements and whumpfs have been reported at all elevations. We have received numerous reports of remotely-triggered avalanches from as far as 500m away which indicates a high likelihood of large propagation within the weak layer. Touchy conditions are expected to remain in place longer than we're normally accustomed to. Recent strong winds out of the SW through NW have created wind slabs on lee features in wind exposed areas at treeline and above. In many wind loaded areas, a slab of up to 2 m thickness overlies the persistent weak layer creating conditions for very large avalanches.Weak basal facets and depth hoar have been noted in reports from some areas, but triggering has now become unlikely. For the most part, the mid and lower snowpack are strong and well consolidated.

Problems

Persistent Slabs

A dense slab from the last series of storms sits on top of a touchy persistent weak layer. This slab has shown a propensity for remote triggering and large propagation. In wind-loaded areas the slab is up to 2m thick.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 6

Wind Slabs

Previous storms winds have created stiff wind slabs on lee terrain features. The primary wind direction was SW but we also had some NW winds. Weak cornices are also a concern and have the potential to trigger large avalanches on the slopes below.

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

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Feb 26th, 2014 2:00PM