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Avalanche Canada swerner, Avalanche Canada

Purcells Avalanche Forecast

Apr 24th, 2019 4:17PM

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

A wintery snowpack still exists at upper elevations. Lingering wind slabs may still be reactive to human triggers.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Cloudy with sunny periods, alpine temperatures near -2 and freezing levels 2000 m. Ridgetop winds light from the southwest

FRIDAY: Mix of sun and cloud with some flurries. Alpine temperatures near -3 and freezing levels 2000 m. Ridgetop wind moderate from the northwest.

SATURDAY: Snow amounts 5-10 cm. Alpine temperatures near -6 and freezing levels 1600 m. Ridgetop wind moderate to strong from the northwest.

Avalanche Summary

On Wednesday, no new avalanches were reported. The avalanche hazard may increase when the sun comes out, especially on solar aspects in the afternoon. Last Saturday morning evidence of large (up to size 3) natural slab avalanche cycle was observed on all aspects above 1500 m; natural avalanches continued throughout the day, two large (2.5-3) natural wind slab avalanches were observed around 3 pm on south aspects. Storm and wind slab avalanches to size 3 were triggered with explosives on all aspects in the alpine (above 2300 m). Impressive results were recorded including sympathetic avalanches to size 2.5; one shot triggered 6 large avalanches as far as 600 m away.

Snowpack Summary

A supportive surface crust caps a mostly isothermal snowpack at lower elevations. In the alpine, the recent snow is likely settling and preserved as cold, wintery snow on north aspects where reactive wind slabs may still linger. A crust is present on all solar alpine aspects and below 2200 m. The strength of the crust will depend on overnight recovery and the speed at which the snowpack warms up during the day.

Weak and sugary faceted grains may remain at the bottom of the snowpack in the alpine, producing a low likelihood but high consequence scenario. Steep, rocky areas with a shallow snowpack are the most likely places to trigger this layer. At lower elevations the snowpack is below threshold.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely - Possible

Expected Size

1 - 2

Use caution around ridges and on leeward features (N-NE slopes) ,slabs may still be reactive to human triggers.

  • Be careful with wind-loaded pockets, especially near ridge crests.
  • Be alert to conditions that change with elevation.
  • Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.

Aspects:

North, North East, East.

Elevations:

Alpine.

Loose Wet

An icon showing Loose Wet

Likelihood

Possible

Expected Size

1 - 2

Expect thin surface crusts to breakdown quickly and turn to moist or wet snow during the day, especially on sunny slopes.

  • Use extra caution on slopes if the snow is moist or wet.
  • Avoid terrain traps such as cliffs and gullies that increase the consequence of small avalanches.

Aspects:

East, South East, South, South West, West.

Elevations:

Alpine, Treeline.

Valid until: Apr 25th, 2019 2:00PM