West Slopes South - South of I-90 to Columbia River

Issued: 6:07 PM PST Tuesday, January 22, 2019
by Dallas Glass

You will need to pay attention and make observations if you travel in the mountains Wednesday. A winter storm will impact locations differently within the West-South zone. In areas where more than 8 inches of new snow falls, you will see greater avalanche danger. In these locations, avoid open slopes greater than 35 degrees.

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Snow and Avalanche Discussion.

A winter storm will impact the West-South region Tuesday night and Wednesday morning. The weather models have struggled with how much water each location will receive. Even though we have some uncertainty with the weather forecast, there are a few trends we can isolate. The volcanoes should receive more water than other locations. Areas such as Crystal and White Pass should be faster to dry out. Since our avalanche forecast depends on this weather forecast, you may find different conditions depending on your location within this zone. We expect avalanche danger to peak overnight during the warmest and stormiest periods. As precipitation ends and temperatures cool, the avalanche danger will slowly decrease.

A firm crust reported up to 6400 feet may create an excellent bed surface for any avalanches Wednesday. In locations where this crust is prevalent, avalanches could run farther and faster than normal.

Avalanche Problems for Wednesday

Storm Slabi

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Photo for Storm Slab

Cracking in the storm snow. (1/18/2019)

Above the rain-snowline, we expect upside-down storm snow caused by warming temperatures, and moderate winds. You are most likely to trigger avalanches in places that received more than 8 inches of new snow, or where wind drifted snow into deeper slabs. Simple observations will help you identify if storm slabs formed overnight. Has the area received more than 8 inches of new snow? Do you see cracking? Can you feel stronger snow over weaker snow? Do you see signs of wind drifted snow? If you answer yes, storm slabs are nearby. In these areas, stay off of open slopes greater than 35 degrees.


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Below the rain-snow line a wet snowpack will develop overnight. You may trigger loose wet avalanches on steep slopes greater than 35 degrees. Even small loose avalanches can be harmful if they carry you into trees, over cliffs, or bury you in a gully. As temperatures cool and the snowpack dries, wet avalanches will become more difficult to trigger.


January 20, 2019

The recent weather pattern of lower accumulation storms (by NW standards) and longer stretches of calm weather should continue as we move into late January. Since January 17th, incremental snow accumulations punctuated with rising freezing levels favored the south and eastern parts of the region. Storm instabilities have risen with storms and gradually subsided.

A storm slab at Mt Baker.

New Snow Problems

Storms over the past week have brought a range of layers from rain crusts, to heavy moist snow, to stiff drifts, to light dry powder. Some storm days, like the 18-19th, saw reactive, but very short-lived avalanches caused by heavy precipitation and wind. Even the longer-lasting avalanche problems, wind slabs, haven't persisted for more than a few days. Where the recent snow is stressing underlying weak layers, more dangerous avalanche conditions have prevailed.

Surface hoar in the East Central zone

Old Snow Problems

Persistent weak layers (PWLs) have been a constant in the eastern zones of the Cascades this winter. As usual, they have been much less problematic at the Passes and west of the Cascade Crest. The latest PWL is a layer of surface hoar, buried around January 17th and found generally east of the Cascade Crest. Buried surface hoar is an active weak layer in the eastern zones and can be found to a limited extent on the eastern edge of the Stevens and Snoqualmie Pass zones. There few, if any, avalanches have been reported on the buried surface hoar. It may be most problematic in open, wind-sheltered terrain, especially well above the valley floor.

You are most likely to find other layers of old weak snow the further you move east from the Cascade crest. Here snowpacks are shallower, more variable, and generally weaker. In some locations, weak snow near the ground can still be found. These basal facets have hung around all season. Digging profiles and using snowpack tests is the best way to gain information about these old persistent weak layers. However, snowpack tests are just one piece of the puzzle. Your terrain decisions shouldn't hinge on any given test result. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.

No Corresponding Mountain Weather Forecast Available