Avalanche Forecast

Issued: Mar 17th, 2014 11:10AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Deep Persistent Slabs and Loose Wet.

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Tuesday

Weather Forecast

Overview: A ridge of high pressure will bring dry conditions to the region on Tuesday. A frontal system will bring moderate snowfall on Wednesday before the dry ridge rebuilds on Thursday.Tuesday: Mix of sun and cloud / Light to moderate northwest winds / Freezing level at 1500mWednesday: 10-20cm of snow / Moderate to strong southwest winds / Freezing level at 1400mThursday: Mix of sun and cloud with light flurries / Moderate northwest winds / Freezing level at 600m

Avalanche Summary

Although observations were limited on Saturday, a size 3 natural persistent slab avalanche was triggered on a south aspect in the north of the region. The avalanche is thought to have failed on a recently buried crust/surface hoar interface. On Sunday observations were somewhat limited; however, widespread storm slab activity to size 2 was reported in the north of the region where recent accumulations were higher. Further south in region several size 1.5 natural storm slabs were reported with a few explosive controlled storm slabs to size 2.

Snowpack Summary

Up to 45cm of recent storm snow exists and has been blown by strong winds into much deeper deposits in lee terrain. These recent storm accumulations overlie crusts on previously sun-exposed slopes and surface hoar in shaded terrain. Rain at lower elevations continued to saturate the snowpack and lower elevation surfaces may now exist as a refrozen crust. Below the new snow, 60-100cm of settled snow has been bonding poorly to buried surface hoar and crusts. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been highly variable in terms of reactivity and is still very difficult to trust. Needless to say, any avalanche at these deeper, persistent interfaces would be large and destructive.Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Problems

Storm Slabs

Recent storm accumulations may take longer to bond due to the presence of buried surface hoar and crusts. Watch for increased triggering in wind-exposed terrain, or when solar radiation is strong.

Choose conservative lines and watch for clues of instability.>Be cautious as you transition into wind affected terrain.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Deep Persistent Slabs

Recent storm accumulations have added stress to a number of persistent weaknesses which exist in the mid and upper snowpack. Any of these weaknesses would be destructive if triggered. Watch for increased sensitivity with forecast solar radiation.

Be aware of the potential for large, deep avalanches.>Good day to make conservative terrain choices.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 5

Loose Wet

With forecast sunny breaks on Tuesday loose wet avalanches will become likely on sun-exposed slopes. Pushy loose wet activity may also trigger deeper, more destructive avalanches.

Watch for clues, like sluffing off of cliffs, that the snowpack is warming up. >Sluffs may trigger deeper instabilities.>

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Mar 18th, 2014 2:00PM