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Archived

Avalanche Forecast

Mar 11th, 2019–Mar 12th, 2019
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
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

Regions: Northwest Coastal.

The snowpack needs time to adjust to the shock of a big, long awaited storm. With surface hoar and sugary facets below the new snow it may take longer than usual to stabilize.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Clearing off and drying out with only flurries. Light to moderate west wind.TUESDAY: Cloudy with sunny periods. Treeline temperatures -5 to -10 C. Light southwest winds.WEDNESDAY: Mix of sun and cloud. Dry. Treeline temperatures around -8 C. Light south wind.THURSDAY:  5 to 10 cm new snow. Moderate south wind. Treeline temperatues -5 to -10 C.

Avalanche Summary

Initial reports from the field today (Monday) suggest whumpfing, cracking, remotely triggered avalanches, and a widespread avalanche cycle on Monday morning.

Snowpack Summary

Widespread and reactive storm slabs and wind slabs. The 40 to 60 cm of storm snow covers a wide variety of surfaces but the key idea is they're all crappy. Avalanche forecasting rule of thumb:  the longer snow is exposed on the surface the less likely it is to bond when covered. We've just covered surface hoar, sun crusts, and a widespread weak faceted (sugary) upper snowpack. Early reports suggest the old surfaces, as old as the Feb 19 surface hoar facets is the critical weak interface so avalanches are running deeper / bigger than might be expected. The upper- and mid-pack weakened with the extended cold drought so there are widespread areas with soft faceted snow, and possibly surface hoar. This sugary soft snow has been reactive in some snowpack tests and there have been some small slab avalanches noted on this layer.The lower snowpack is generally considered strong.

Avalanche Problems

Storm Slabs

Previous weaknesses in the upper snowpack (30 - 40 cm of sugary facets) may become activated resulting in larger avalanches than expected. See Persistent Slabs below.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1.5 - 3

Persistent Slabs

Higher new snow amounts are making old surface hoar and sugary facets in the upper snowpack layers to watch.
Storm or wind slabs may step down to deeper layers resulting in large avalanches.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 3