Avalanche Forecast

Issued: Apr 20th, 2017 4:00PM

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

garth lemke, Parks Canada

Jasper.

Large cornices are unstable and can trigger big avalanches if they fall. Avoid all terrain below cornices. Gauge how quickly the overnight crust breaks down during the day relative to increasing danger.

Summary

Weather Forecast

Weather predictions have been unreliable for precipitation. Thursday night may bring 12mm, rain below 1900m turning to 10-15cm of snow later with overnight freezing level dropping to 650m. Friday-Saturday will be sun, freezing level 2200m or higher by the afternoon. Winds will remain light below 2300m but may gust moderate above 2400m on Friday.

Snowpack Summary

The top 30cm of snow is moist or wet depending on aspect and elevation. Melt freeze crust up to 2500m on S aspects. Mid-pack is solid and bridging the weak base. The bottom 30cm of the snowpack consists of weak facets and depth hoar mixed around the Nov rain crust. Below 1500m there is no snow.

Avalanche Summary

Thursday's Icefields patrol noted three size 1.5 loose wet at 1800m on S aspect. Also noted, a couple of cornice triggered size 2.5 deep persistent avalanches running on ground on West aspects at 2500-2800m. The size 2.5's appeared to be around 48 hours old.

Confidence

Timing or intensity of solar radiation is uncertain

Problems

Deep Persistent Slabs

The deep instability could be triggered by a cornice failure. It is well bridged by a solid mid-pack; however, consider this problem becoming more active particularly on South aspects as the day warms up or the sun comes out.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Loose Wet

The snowpack will warm during the day with potentially rain Thursday night below 1900m. Depending on Thursday nights' temperature and the amount of sun on Friday, the danger may increase from low in the morning to considerable by early afternoon.

Start and finish early before the surface crusts melt.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Cornice failures are still being noted on West aspects 2500-2800m. Give them a wide berth as their failure is hard to predict but increases with sun, warmth, wind-loading, or new snow.

Give cornices a wide berth when travelling on or below ridges.Avoid travel on slopes that are exposed to cornices overhead.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Apr 21st, 2017 4:00PM