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Archived

Avalanche Forecast

Dec 17th, 2018–Dec 18th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Cascades - South East.

Very dangerous avalanche conditions are developing. Heavy snowfall, strong wind, and a changeover to rain at lower elevations are likely to push our weak snowpack over the edge and cause an avalanche cycle. Avoid travel in avalanche terrain, including runout zones in valley bottoms.

Discussion

Discussion 

Persistent weak layers have been identified in the adjacent East Slopes Central forecast zone. Although we have no information about snow conditions from this zone, the Persistent layers are likely to exist here as well.

Heavy snow, changing to rain early Tuesday may bring these layers to the breaking point. Avoid all slopes where avalanches may start, stop, and run.

Below and near treeline, warming temperatures will produce wet snow avalanches on Tuesday. 

Avalanche danger may be slightly mitigated due to low snow conditions below treeline, but even here dangerous avalanche conditions exist and exposed terrain will be very hazardous in a small, but powerful loose wet avalanche.

Forecast Schedule

General avalanche and snowpack information will be provided during the winter. However, at this time we do not have enough specific snowpack information to issue an avalanche hazard rating for the East Slopes South zone.  

Snowpack Discussion

Updated Regional Synopsis 20181216

Dangerous and fickle avalanche conditions remain as active weather continues into the week. Thick slabs of new snow (2-5 feet) are perched above a weak layer of faceted crystals. Avalanches triggered on this layer could be very large and life threatening.

Reports continue to come in of very large natural and triggered avalanches in the northern and eastern zones. For perspective, several of these slides have been classified as D3, or large enough to destroy a house. You can find similar snowpack structure responsible for these avalanches in many other locations throughout the Cascades, including Stevens and Snoqualmie Passes.

Anyone accessing alpine areas should limit their exposure to areas where avalanches start, run and stop. In some places the weak snow will talk to you by whumpfing and cracking. In other places, the heavy blanket of new snow is thick enough that it can give a false sense of stability while it masks the dangerous layering below.

Approximate snow totals from 12/10 - 12/16:  

  • Mt. Baker: 75”

  • Washington Pass: 35”

  • Stevens Pass: 42”

  • Snoqualmie Pass: 36”

  • Paradise: 51”

  • Crystal Mt Base: 29”

  • Mt. Hood Meadows: 21”

  • Olympics: mix of rain and snow, no net gain

The change in the snowpack is pretty dramatic with elevation. Height of snow decreases rapidly below 4500’ at Baker and Washington Pass, 5500’ at Crystal/Rainier. The Passes have better low elevation coverage, but it's still pretty thin below 4000’. With additional warm storms in the forecast, this pattern is expected to continue for awhile. Mt. Hood and Hurricane Ridge have low snow coverage below 5000’.

If you're out in the mountains, please let us know what you see.

Be cautious and get home safe.