Avalanche Forecast

Issued: Apr 22nd, 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, Wind Slabs and Persistent Slabs.

tim haggarty, Parks Canada

Little Yoho.

Clear skies will bring strong solar heating but likely decent re-freezes Monday and Tuesday mornings. Start early and finish early. A poor recovery, calm winds and high freezing level are likely for Wednesday.

Summary

Weather Forecast

Midday clearing Sunday generated moist snow on south aspects despite the cool temperatures. This clearing marks the start of formation of a ridge of high pressure. Expect a 2000m freeze level Monday, 2500m Tuesday (with some significant winds), and 3300m Wednesday (little wind) with strong solar inputs. Models show a poor recovery Tuesday night.

Snowpack Summary

5-10cm of snow with very strong SW winds on Saturday has formed new wind slabs above treeline. Buried temperature crusts exist to 2000m on all aspects and to ridge tops on solar slopes, including the Mar 15 sun crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist near valley bottom.

Avalanche Summary

Small soft windslabs were reactive to ski cutting today in isolated locations in the lee of alpine features. Forecasters observed a powder cloud sweep the E face of Fay around 13:00 and suspect a sz 2 cornice or windslab failure. Lots of loose wet avalanche activity on steep solar aspects in the past several days once the sun comes out.

Confidence

Problems

Loose Wet

Expect decent freezes for Sunday and Monday evenings to build crusts that will take time for the sun to break down as the day warms up. Start early and finish early to avoid unstable moist snow. Tuesday night's recovery looks a little shaky.

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

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Wind Slabs

Saturday, 10 cm of snow and strong SW winds formed soft slabs in the alpine that proved to be reactive to skiers in only isolated locations. Buried winds slabs from the previous week may still be present in isolated alpine locations.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.The recent snow may now be hiding windslabs that were easily visible before the snow fell.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 1.5

Persistent Slabs

A few avalanches last week were deeper than the most. Some clearly stepped down to the March 15 crust. On shaded aspects events were likely sliding on facets formed at the same interface. This may wake up again with significant heating.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Apr 23rd, 2018 4:00PM