Avalanche Forecast

Issued: Mar 13th, 2015 8:56AM

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

pgoddard, Avalanche Canada

South Rockies.

Weather models are having trouble with the specifics of this weekend's weather. Any time it is raining, snowing or blowing, assume elevated avalanche danger.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Two pulses of precipitation are expected this weekend. The first, on Saturday, brings 5-15 mm rain with strong to gale SW winds and a freezing level near 2400 m. Late on Sunday and into Monday, it looks more hopeful for snow (10-15 cm) with the freezing level closer to 1200 m. Winds switch briefly to the NW before swinging back to the SW. Weather models are not handling the developing situation well, so I have little confidence in the specifics of the weather forecast.

Avalanche Summary

On Tuesday, our field team members in the north Elk Valley experienced several whumpfs on south facing treed terrain at 2200 m. They also experienced a whumpf of a hard slab near ridge top at 2450 m and saw a deep slab release on a sunny aspect that probably occurred some time in the last week. Recent loose wet avalanches up to size 1.5 appeared to have been triggered by solar warming. On Sunday, a skier-triggered slab released on a weak layer near the ground in Kananaskis Country. Rain, snow and wind forecast for the weekend are likely to drive natural avalanche activity.

Snowpack Summary

Rain is likely to weaken the snowpack below about 2000 m on Saturday, and may cause a natural cycle of loose wet or wet slab avalanches. At low elevations, thin snowpack areas may simply melt. On the highest peaks, new snow will probably be shifted by strong winds into slabs lee to the SW. Cornices may develop. The most prominent snowpack feature is a thick crust 10-30cm below the surface, extending up to around 2200m elevation. The support of this crust is breaking down in response to warm temperatures. Persistent weak layers below this crust still react in snowpack tests and could wake up with continued warming or loading.

Problems

Loose Wet

Rain is expected to weaken an already moist snowpack, and may drive a loose wet or wet slab avalanche cycle.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Cornices become weak with heating, so avoid exposing yourself to them.>Avoid steep or committing slopes if the snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Deep Persistent Slabs

We have concerns about this problem "waking up" with warm temperatures. A crust that previously isolated deep weaknesses has broken down with warming. Recent whumpfing indicates unstable snow.

Be aware of thin areas and rock outcroppings where you are more likely to trigger a deep slab.>Avoid large slopes during times of warm temperatures.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Wind Slabs

Areas of wind slab may be encountered near ridge top.

Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 14th, 2015 2:00PM