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Avalanche Forecast

Mar 20th, 2017–Mar 21st, 2017
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
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: South Columbia.

We've weathered the storm but we're not out of the woods yet. There's a great blog post on critical factors to watch out for this spring. Click here for details.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

We're looking at classic unsettled spring weather for the forecast period: cloudy with isolated (sometimes intense) flurries.TUESDAY: Isolated flurries (local amounts 5-10cm possible) / Light to moderate southeast wind / Freezing level 1500mWEDNESDAY: Broken skies with isolated flurries (local amounts 5-10cm possible) / moderate south wind /Freezing level 1600mTHURSDAY: Flurries in the morning with 5cm possible / Moderate southwest wind / Freezing level 1400m

Avalanche Summary

We had a widespread natural avalanche cycle (to Size 4.5) at all elevations and aspects during the recent storm, including multiple adjacent avalanche paths running simultaneously with 1 Km wide propagation.Many of these avalanches ran in the storm snow with some also stepping down to persistent weaknesses (see snowpack summary below) deeper in the snowpack. Widespread wet slabs and loose wet avalanches were also reported below treeline.Of particular concern are the ongoing large destructive avalanches (some scrubbing to ground) that have been occurring daily: one or two deep spooky avalanches in each bulletin region of the Columbia Mountains. See the link in the headline for detailed discussion of these low probability, high consequence events.

Snowpack Summary

We had heavy wet snow (or rain up to 2000m in places) and strong to extreme southerly winds during the weekend's storm. Temperatures also warmed up significantly. The end result: Widespread storm slabs and wind slabs at treeline and above, with significant cornice growth as well.The most recent storm snow (totals of 20-50cm) sits on older windslabs (or soft slabs) at treeline and above. Below 1900m, the new snow (with a thin breakable surface crust) sits on a melt-freeze crust from rain events last weekend. Reports so far are that the new snow is bonding well to the old crust, but that the storm snow instabilities are showing some reactivity to rider traffic.Approximately 100-140 cm below the surface you may find the late-February persistent weakness / crust interface. This layer has woken up from time to time as smaller avalanches still have to potential to 'step down' and trigger this layer.The deep mid-December facet layer (and November raincrust) still linger at the bottom of the snowpack and are the suspected culprit (running to ground) in a Glacier National Park avalanche. See here for the spooky picture.

Avalanche Problems

Storm Slabs

Warm storm snow on Saturday and strong southwest wind created a storm slab problem. The snowpack will need time to adjust to the new load - stick to low angled terrain (with no overhead hazard) and avoid sunny slopes if/when the sun comes out.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Persistent Slabs

Various persistent weaknesses throughout the snowpack create the potential for large step-down avalanches. Heavy loads such as a smaller storm/wind slab avalanche or even a cornice failure will increase the likelihood of triggering these layers.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for wide propagations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4