Archived

Avalanche Forecast

Nov 24th, 2017–Nov 25th, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: South Rockies.

If the rain-soaked snow freezes as expected through the weekend, avalanche hazard will follow a decreasing trend until the next storm on Sunday. Please treat this forecast as an initial assessment, as we have little information at this time.

Confidence

Low - Due to the number of field observations

Weather Forecast

We're looking at relatively benign weather until Sunday afternoon, when a brief but intense cold front will bring rain and then 10-15cm snow by Sunday night. Saturday: Dry. Freezing levels initially around 1500 m, but increasing later in the day. Light southwesterly winds, increasing in the afternoon.Sunday: Rain early afternoon changing to flurries (10-15 cm possible). Freezing levels 2200m decreasing to surface by the evening. Winds moderate southerly. Monday: Scattered flurries. Freezing level around 1200 m. Moderate westerly winds.

Avalanche Summary

There are few observers right now. Several loose wet avalanches to Size 1 were reported at the tail end of the rains (Thursday). Some persistent slab activity to Size 2.5 was reported to the north in Kananaskis country. Elevations ranged from 2400 to 2600m on Northeast through Northwest aspects. I suspect avalanche activity will taper off with cooling temperatures on the weekend.

Snowpack Summary

Rain and warm weather have resulted in a widespread wet upper snowpack. The freezing level rose to approximately 2700 m on Wednesday and Thursday meaning very few places, if any, will have escaped the melt. The last three days have seen the snowpack diminish by approximately 20-30 cm.Some areas saw 5-15 cm of snow at the tail end of the storm and the possibility of thin windslabs exists. Expect treeline snow depths of around 45 cm in the Elk Valley and more like 80 cm further south in the Flathead in sheltered areas. A crust that formed around Halloween has been reported within the snowpack that may lie around 40-50 cm below the surface.

Avalanche Problems

Persistent Slabs

We know there's a crust buried approx. 50cm below the surface, but don't know much about how likely avalanches are on it. Once there's a new thick crust on the surface, this lower layer may become less of a problem. Until then, assume it's a player.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Start with lower angle slopes before gradually working up to steeper objectives.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Wind Slabs

5-15cm of new snow fell at the tail end of the storm, as temperatures cooled and the rain turned to snow. Watch for wind slabs from redistributed snow on north easterly slopes at higher elevations.

Use caution in lee areas. Recent wind loading may have created wind slabs.If triggered, wind slabs may step down to deeper layers including persistent slabs (see above).

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2