Avalanche Forecast

Archived

Dec 22nd, 2018–Dec 23rd, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

You are likely to find reactive snow on higher elevation slopes near ridgelines. We have no recent snowpack observations from this area, so take the time to properly assess conditions before engaging in avalanche terrain.

Discussion

Snow and Avalanche Discussion

The past week featured fluctuating snow levels and long stretches of high winds, followed by cool temperatures. A wet snowpack began to refreeze Thursday night, a trend that will continue through Sunday. Expect extreme variation in snow depths in the Hurricane Ridge area due to recent stormy conditions. The below treeline snowpack is likely still marginally thin to support avalanches below 4500-5000'. We have not had any snowpack observations since last Sunday, and even those were limited due to widespread power outages and road closures at the Park. Keep this in mind and buffer in the extra uncertainty while making terrain selections.

Forecast schedule

For the 2018-19 winter season, avalanche hazard ratings will be issued for the Olympics Friday through Sunday and during holidays.

On days that the Hurricane Ridge road is closed, No Rating will be applied. We will continue to provide general snowpack and weather summaries for the Hurricane Ridge area even when No Rating is issued.

Snowpack Discussion

Regional Synopsis: December 19, 2018

Why has the avalanche danger been so high for so long? Two reasons: A very active and wet weather pattern combined with a widespread persistent weak layer.

For perspective, the approximate snow totals from 12/9-12/19 are:

Mt Baker: 102”
Washington Pass: 55”
Stevens Pass: 76” mid-mountain
Snoqualmie Pass: 68” mid-mountain
Crystal Mountain 70” Green Valley
Paradise: 78”
Mt Hood Meadows: 44” mid-mountain
Olympics: 48”

In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause of numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess. In short, the scenario is tricky and getting more dangerous by the day.

Higher snowfall totals along the Hwy 542 corridor/Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south of the Mt. Baker area, so we have not yet experienced a widespread cycle in other areas.

When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.

Be patient and continue to stick to lower angle slopes with nothing above you. This is a good time to avoid areas where avalanches can start, run, and stop.

We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.