Avalanche Forecast

Issued: Feb 27th, 2014 8:20AM

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.

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 - Timing or intensity of solar radiation is uncertain

Weather Forecast

The ridge of high pressure continues to dictate conditions for the forecast period. Cold, dry arctic air scheduled to move back into the region. Strong arctic outflow winds have already begun and will continue into the coming weekend. For a more in-depth look at the weather, check out the latest: Weather Outlook Thursday night: Cloudy periods, freezing level at valley bottom, trace of precipitation,...ridge top winds, light to 25Km/h.Friday: Sunny, freezing level at valley bottom, trace of 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 north gusting to 40 Km/h.Sunday: Sunny, freezing level at valley bottom, trace of precipitation, ridge top winds light.

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 from the last series of storms now lies above a touchy, persistent weak layer. This slab has shown a propensity for remote triggering and propagating over wide distances. In wind-loaded areas the slab may be up to 1.5 metres 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

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Wind slab development may now switch to south and south west slopes as the incoming arctic air drives down from the north east. This may build cornices in places not usually seen.

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

Expected Size

1 - 4

Valid until: Feb 28th, 2014 2:00PM