Avalanche Forecast

Issued: Apr 27th, 2018 4:00PM

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

tim haggarty, Parks Canada

Little Yoho.

Expect a modest recovery and strong daytime heating again on Saturday before the clouds roll in. Early morning rain is possible Sunday and will likely contribute to a poor recovery at lower elevations before cooling leads to snowfall later in the day

Summary

Weather Forecast

Temperatures have been slightly inverted with better freezes at valley bottom, but temperatures will stay above freezing in the alpine Friday evening. Saturday will see solar heating progress quickly with clear skies until midday when winds pick up and bring cloud later in the day. Sunday morning may bring rain below 2000m turning to snow by noon

Snowpack Summary

Crust or moist snow on all solar aspects depending on temperatures. Buried temperature crusts to 2000m on all aspects and to ridge top on solar slopes, including the Mar 15 crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist below treeline in the afternoons.

Avalanche Summary

Ongoing wet snow avalanches typical for this time of year are occurring with daytime heating. Both loose snow and wet slabs are common with slabs occasionally stepping down to mid-pack and basal layers. These vary by aspect and elevation but can travel far as they entrain isothermal snow. Many events have reached full path over the last two days.

Confidence

Problems

Loose Wet

Loose wet avalanches have been common over the last couple of days and will continue Saturday until cooling takes over Sunday. Even small wet slides are very powerful and destructive. Starting and ending very early are the best defense.

Watch for clues, like sluffing off of cliffs, that the snowpack is warming up. Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Wet Slabs

As the upper layers of the snowpack are becoming moist persistent weak layers are failing as wet slabs. Most of these events are limited to shallow crusts on solar aspects however some slopes have seen enough heating to allow releases on older layers

Avoid shallow snowpack areas where triggering is more likely.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Cornices

Cornice failures are occurring on a regular basis now with warm temperatures and intense solar inputs. These large triggers have caused failures on the persistent weak layers deeper in the snow pack over the last couple days.

Minimize exposure to overhead hazard from cornices.Cornices become weak with daytime heating, so travel early on exposed slopes.

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

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Apr 28th, 2018 4:00PM