Avalanche Forecast

Issued: Mar 30th, 2017 4:15PM

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

swerner, Avalanche Canada

Purcells.

Warming and solar induced avalanches are likely. Smaller wind slabs, storm slabs or cornice fall could "step down" and release persistent weak layers resulting in large avalanches.

Summary

Confidence

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

Weather Forecast

Drier, sunny conditions expected on Friday and then back to unsettled weather with a mix of sun, cloud and warming for the weekend.Friday: Mix of sun and cloud. Alpine temperatures near -2 and freezing levels 2000 m. Ridgetop winds light from the South.Saturday: Trace of new snow. Alpine temperatures near -5 and freezing levels 1800 m. Ridgetop winds moderate -strong from the West.Sunday: Mix of sun and cloud with isolated flurries up to 5 cm. Alpine temperatures near -7 and freezing levels 1300 m. Ridgetop winds light with strong gusts from the West.

Avalanche Summary

On Wednesday, a couple of larger storm slab avalanches were reported. They were explosive controlled size 2 and size 3 from South aspects 1800 m and above. There was also one skier controlled size 1.5 slab avalanche that failed on a crust from a South aspect around 2200 m. On Friday natural avalanche activity may occur and rider triggering is likely, especially with the strong influence of solar radiation, warming and wind. Fragile cornices are also suspect, they are large enough and act as heavy triggers for deeper slab avalanches to release on the slopes below. If you're traveling below treeline where the avalanche hazard is lower than it is in the alpine you should remain diligent with your terrain use, mitigate overhead hazards by avoiding or lingering in run-out zones where large avalanches could come down from above. Check out the recent Forecasters' Blog here

Snowpack Summary

10-30 cm of recent snow has fallen at upper elevations and caps a sun crust on solar aspects. This brings 40-60 cm of accumulated snow over the past week. This recent snow overlies a widespread crust below 2300 m and higher on solar aspects. Alpine wind has recently been strong mainly from the SW and has loaded leeward slopes in exposed terrain at treeline and in the alpine. Large, fragile cornices also exist along ridgelines. At higher elevations, the February crust/facet layer is now down around 130-150 cm and has been reactive with several avalanches recently releasing on it. It is expected to be most reactive in the alpine where the snowpack remains dry. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have stepped down to these layers recently resulting in very large avalanches. These layers remain a concern during this stormy period ending with warmer temperatures and sunshine. The snowpack does not adjust well to change, and these deeper weak layers should remain on your radar through the forecast period.

Problems

Wind Slabs

Recent wind from the SW has redistributed the new storm snow in exposed terrain at higher elevations forming reactive wind slabs. Cornices are large and may become weak with daytime warming, sun exposure, or during stormy periods.

Minimize exposure to overhead hazards and sun exposed slopes when the solar radiation is strong.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

A cornice fall or smaller slab avalanches could trigger deep, destructive avalanches on buried weak layers. There is a low likelihood of triggering but a high consequence if triggered. These avalanches would likely run full path.

If triggered, wind slabs or cornices may step down to deeper layers resulting in large avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Warmer temperatures and rain may deteriorate the lower elevation snowpack, initiating loose wet avalanches that may slide easily on a buried crust. If the sun shines this problem could extend high into the alpine on solar aspects.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Valid until: Mar 31st, 2017 2:00PM