Avalanche Forecast

Issued: Mar 18th, 2016 9:21AM

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

bcorrigan, Avalanche Canada

Kootenay Boundary.

With warming temperatures, avalanches may run naturally, especially on steep sun affected slopes. Cornices have grown large and will weaken with rising temperatures. Be conservative with terrain choices.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

The ridge will remain in place through Saturday as a southwesterly flow brings warm air into the region for Saturday and Sunday. FRIDAY: The freezing Level is forecast to climb above 1500 m, returning to valley bottom overnight, light easterly winds, with no precipitation forecast. SATURDAY: Freezing level starting at valley bottom climbing to 2500 m in the afternoon, light to moderate southwest winds, no precipitation. No overnight temperature recovery expected. SUNDAY: Freezing level holding at 2500 m, moderate southwest winds at ridge top, light precipitation expected. Increasing cloud cover will likely trap warm air leading to a greenhouse situation.Â

Avalanche Summary

It's been a very active period with numerous large natural and human triggered avalanches being reported over the last few days. On Wednesday a skier remote triggered a cornice failure from a few meters away on a north/northeast facing slope around 2100 m in the Rossland range. When the falling chunks of cornice impacted the slope below it triggered a very large (size 3) avalanche that ran on the March 6th crust. Natural cornice failures were also reported. A second skier triggered avalanche (size 2) was reported on a northeast facing feature near 2000 m. Numerous loose wet avalanches to size 1.5 were also reported from solar aspects. ( facing southerly) On Monday a sleddder triggered a size 2 avalanche on a north facing feature at 1900 m failing on the late February surface hoar which resulted in a fatality in the Mt. Mackie area southwest of Castlegar.

Snowpack Summary

The recent storm snow of 40 to 60 cm continues to settle above a mix of crusts at treeline and below. In some drainages these storm slabs may be sitting on a thin crust that was initially buried on March 11th. A second crust, (the early March melt/freeze crust) can be found down 50 to 80 cm. The late February (Feb 27th) persistent weak layer of buried surface hoar down is now down 70 to 120 cm and has been the interface for some large avalanches. I suspect that this weak layer is more prominent on northerly (shaded) aspects at and above 1700 m. This surface hoar layer may also be associated with a crust on solar aspects. With the forecast of sun and strong solar radiation, triggering this deep weak layer may become easier. Pay attention to moist or wet surface snow as a sign that solar radiation is strong and deep weak layers may become reactive.

Problems

Storm Slabs

Recent storm slabs and cornice growth continue to be a concern for human triggering. Forecast strong solar radiation may increase the reactivity of the slab and the likelihood of triggering large destructive avalanches.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Avoid freshly wind loaded features.>Choose well supported conservative lines and watch for clues that indicate instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

Surface hoar buried down about one metre has been recently triggered by light loads like a single skier or rider. Strong solar radiation and warm daytime temperatures may increase the likelihood of triggering.

Surface avalanches in motion could step down and initiate persistent slab avalanches which have the potential to be large and destructive.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Loose Wet

Strong solar radiation and warm temperatures may result in loose wet snow releasing naturally from steep terrain. A skier or rider may also trigger a loose wet avalanche that could affect buried weak layers and trigger a large destructive avalanche.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 19th, 2016 2:00PM