Avalanche Forecast

Issued: Mar 19th, 2016 9:14AM

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 - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

The high pressure ridge over the interior of the province should remain until late Sunday afternoon. Warm southerly winds will continue driving the freezing level to 2500 m late Saturday through Sunday, then begin to drop late on Sunday afternoon to around 1500 m. No overnight temperature recovery expected. Precipitation is forecast to begin late Sunday afternoon and continue through Tuesday with 10 to 15 mm forecast, most likely falling as rain below 1500 m. Wednesday should be dryer with the freezing level dropping to 1000 m overnight.

Avalanche Summary

Reports of natural and human triggered avalanches have dropped off in the past few days. Earlier in the week a skier remotely 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 have also been 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 have also been reported on solar aspects. ( facing southerly) .

Snowpack Summary

The recent storm snow of 40 to 60 cm continues to settle above multiple crusts at treeline and below. In some valleys these storm slabs may be sitting on a thin crust that was 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. We 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 the potential is there for deep weak layers to become reactive.

Problems

Storm Slabs

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

Choose well supported conservative lines and watch for clues that indicate instability.>Avoid freshly wind loaded features.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be careful with wind loaded pockets while approaching and climbing ice routes.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

Buried surface hoar about one metre down might be triggered by light loads like a single skier or rider especially on north aspects. Strong solar radiation and warm daytime temperatures may increase the likelihood of triggering on south aspects.

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

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 20th, 2016 2:00PM