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

Issued: 6:05 PM PST Sunday, January 20, 2019
by Dennis D'Amico

Cooler temperatures and a stiff NW wind will transport snow at ridge-crest, building shallow wind slabs on steep unsupported slopes. In wind sheltered areas or at lower elevations, you should find generally safe avalanche conditions with a few inches of snow above a firm rain crust. Continue to stop and dig in the colder part of the zone that includes Chinook and White Pass, looking for weaker snow below more recent denser snow.

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Snow and Avalanche Discussion

A strong weather system blew through the region Friday night bringing high winds and rising snow levels that pushed rain into the near treeline band including up to ridge-crest in the Crystal Mt. area. Only shallow amounts of new snow fell on top of a refreezing rain crust. This event was followed by 3 inches of new snow that fell evenly across the zone Sunday along with very little wind. 

In the colder part of the zone, weak snow comprising of buried surface hoar or near surface facets may be lurking underneath the most recent storm snow. If traveling above the local rain-line, particularly in the Chinook or White Pass area, you'll need to travel cautiously if you think a persistent weak layer was recently buried. Remember that slab avalanches failing on persistent weak layers can break well above you from lower angled terrain.

If the sun comes out on Monday, expect small loose avalanches on very steep sunny slopes.

Avalanche Problems for Monday

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Photo for Wind Slab

Small human triggered wind slabs (1/12/2019)

On Monday, observe where winds are transporting snow and if shallow wind slabs are building near and above treeline. Approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and any slope less than 35 degrees.


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 form 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