Avalanche Forecast

Issued: Apr 9th, 2012 11:50AM

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

Avalanche Canada swerner, Avalanche Canada

Freezing levels are expected to rise to 3000 m for the next two days. Treeline temperatures steady near +6 accompanied by intense solar radiation and limited re-freeze. Expect danger ratings to remain elevated through the forecast period.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Thursday

Weather Forecast

The beautiful weather we've been seeing over the past few days will start to change as a dominating upper ridge begins to break down, and turn to a warm Southerly flow. A series of systems caught in this flow will affect the region through to Friday. Tuesday: Continued sunny, cloudless skies with light ridgetop winds from the SW. Freezing levels could reach 3000 m. A temperature inversion may redevelop bringing warmer alpine temperatures through the night. Treeline temperatures steady near +6 C. Wednesday: A mix of sun and cloud with possible afternoon rain showers. Treeline temperatures near +10, with freezing levels 3000 m. Thursday: Possible 30-40 mm of precipitation (mix rain and snow) through the day, with freezing levels falling to 1500 m. Ridgetop winds moderate from the West.

Avalanche Summary

On Sunday one skier triggered slab avalanche was reported. This occurred on a North aspect @1950, running 40 m wide and 100 m in length. Other observations from he field have indicated many loose wet slides from steep solar aspects up to size 2. Last week's storm snow is now fairly well settled which has scaled avalanche activity way back. The only avalanche activity reported Saturday was from a high elevation NW facing slope that failed naturally producing a size 2.5 avalanche.

Snowpack Summary

Mild temperatures and spring-like conditions continue to drive rapid settlement of last week's storm snow. A sun crust exists on solar aspects, while Northerly slopes host dry, wintery conditions down to 1400 m. Below the surface, the upper pack seems to be settling quickly. This includes an average of 100 cm overlying the March 26th interface .The March 26 interface consists of a melt/freeze crust on all aspects except true north treeline and alpine, where small surface hoar (5mm) is present in sheltered places. The bond at this interface is gaining strength, with lingering concerns on true south aspects where the crust is thickest and where the surface hoar lurks. The snow at lower elevations has become moist and heavy during the warm sunny days, then re-freezing at night creating true spring like conditions. The persistent early February surface hoar lingers deep in the snowpack and may once again become a player mid-week when the region goes several days without a good overnight refreeze or recovery. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.

Problems

Loose Wet

An icon showing Loose Wet
Strong sun, and freezing levels up to 3000 m is forecast for Tuesday/Wednesday. Watch for loose wet avalanches, with the potential for deeper slab avalanches on slopes that bake all day under the strong spring sun.

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

Elevations: Alpine, Treeline.

Likelihood

Very Likely - Certain

Expected Size

1 - 5

Cornices

An icon showing Cornices
Large, looming cornices have formed. Cornices receiving direct sun will eventually grow weak with potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Pay attention to what's happening above you.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 7

Persistent Slabs

An icon showing Persistent Slabs
The March 26th layer should be on your radar through the forecast period. It's now down 100 cm, which could create a large avalanche if triggered. I'd be wary of triggering on steep unsupported slopes, especially on Southerly aspects.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 7

Valid until: Apr 10th, 2012 9:00AM

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