Avalanche Forecast Purcells

Date Issued: Valid Until:

Avalanche Canada jsmith, Avalanche Canada

Avalanche Forecast

Thu Apr. 25th · 4:29PM

Alpine

Danger Ratings Moderate

Treeline

Danger Ratings Moderate

Below Treeline

Danger Ratings Low
Wind Slabs Wind Slabs
Loose Wet Loose Wet

Alpine

Danger Ratings Moderate

Treeline

Danger Ratings Moderate

Below Treeline

Danger Ratings Low

Alpine

Danger Ratings Moderate

Treeline

Danger Ratings Moderate

Below Treeline

Danger Ratings Low

Lingering wind slabs may still be reactive to human triggers; especially on lee features below alpine ridgetops.

Confidence

Low - Due to the number of field observations

Weather Forecast

THURSDAY NIGHT: Increasing clouds / Light, southwesterly winds / Alpine low -4 C / Freezing level 1700 m.

FRIDAY: Mix of sun and cloud with isolated flurries; 0-3 cm. / Light, northwesterly winds / Alpine high 0 C / Freezing level 2000 m.

SATURDAY: Cloudy with flurries; 3-10 cm. / Light to moderate, westerly winds / Alpine high -5 C / Freezing level 1500 m.

SUNDAY: Sunny / Light, northeasterly winds / Alpine high -5 C / Freezing level 1500 m.

Avalanche Summary

No new avalanches were reported in this region on Wednesday. However, there are currently very few professional observers submitting daily observations. Please submit your observations to the MIN. Photos of avalanches or current conditions are particularly useful.

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 up to 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 to mountain tops and below 2200 m on all aspects. The strength of the crust will depend on overnight freeze 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  or highly variable snowpack depth are the most likely places to trigger this layer.

Below treeline, snow is disappearing rapidly.

Problems

Wind Slabs

Wind Slabs

Lingering wind slabs may still be reactive to human triggers; especially on lee features below alpine ridgetops.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2
Loose Wet

Loose Wet

Any appearance of the strong April sun can initiate a loose wet avalanche cycle. The likelihood of loose wet avalanches increases as temperatures warm through the day and/or if the sun comes out for a prolonged period of time.

  • Avoid terrain traps such as cliffs and gullies that increase the consequence of small avalanches.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if the snow is moist or wet.
  • Cornices become weak with daytime heating, travel early on exposed slopes.

Aspects: East, South East, South, South West, West.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5