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Archived

Avalanche Forecast

Dec 22nd, 2019–Dec 23rd, 2019
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
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

Regions: Glacier.

Solar input could initiate another large natural avalanche cycle today!

Deep snow and tree-well immersion is also a very real danger today as the new snow will take time to settle and bond to old layers.

Weather Forecast

Today will be the first day without any precipitation in some time. A benign weather pattern with cooling temperatures and clearing skies is the trend for this week.

A mix of sun and cloud today.  Freezing levels are forecast at 1000m with an alpine high of -6C.

Snowpack Summary

The Atmospheric River dumped 75mm of precipitation since Thursday afternoon. The Dec 11th SH (5-12mm) is now down 90-120cm, and sits on a rounding midpack. The Nov 23 SH/Cr is down 160-185cm. Early season crusts still persist in the lower snowpack.

Avalanche Summary

Over the past two days, two full rounds of artillery control East and West of Rogers Pass summit produced numerous avalanches up to size 3.5 on all aspects and elevations. Slides were releasing in the storm snow then overloading the persistent slab of Dec 11, SH, down 90 - 120 deep.

Confidence

Timing or intensity of solar radiation is uncertain

Avalanche Problems

Storm Slabs

Solar input today could initiate another large natural avalanche cycle! Storm slabs are expected to be widespread and sensitive to human triggering.

  • 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: All elevations.

Likelihood: Very Likely

Expected Size: 1 - 3

Persistent Slabs

The Dec 11th Surface Hoar(SH), size 5-12mm is down 90cm+. This sliding layer was reactive in our control yesterday. Large avalanches will reach valley bottom.

  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 2 - 3.5

Deep Persistent Slabs

The Nov 23 melt freeze crust is down deep in the snowpack. This layer may reach threshold for overload from avalanches triggered in upper snowpack layers or a large cornice release. The resulting avalanches will be very large.

  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2.5 - 3.5