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East Slopes North - Canadian Border to Lake Chelan

Issued: 6:11 PM PST Tuesday, January 22, 2019
by Matt Primomo

Another round of snow with warming temperatures and strong winds will create slab avalanches. The additional shot of snow will continue to stress multiple deeper weak layers in the snowpack in the East Cascades, which could create very large avalanches. Avoid avalanche terrain if you see recent avalanches, shooting cracks, or hear whumphs. 

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Snow and Avalanche Discussion:

Observers continue to find instabilities and on a layer of buried surface hoar from January 17th, even at elevations as low as 5,000ft. Several natural and human triggered avalanches were reported over the weekend in the Washington Pass area. These were  within new snow and a few were likely on the 1/17 layer. Deeper persistent weak layers still exist within the snowpack, especially further east in the range. All over the East Cascades, these layers will be further stressed with an added load overnight into Wednesday. Will this be the straw that breaks the camel's back?

Be sure to check the observations page for a number of excellent recent entries!

Avalanche Problems for Wednesday

Storm Slabi

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Recent Storm Slab (1/22/2019)

Heavy snow, warming temperatures, and strong winds overnight into Wednesday will form thick slabs. Winds will drift the new snow into very deep slabs at upper elevations. What is the new snow sitting on? Is there strong over weak? Is the new snow cracking, or do you see recent avalanches? Tomorrow is a good day to avoid slopes steep enough to avalanche, including small gully like features that could increase your consequences of even a small slide. Beware of the large avalanche paths in the area as well, and don’t get up underneath large slopes.

 

Persistent Slabi

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Recent persistent slab (12/31/2018)

Put a large buffer of terrain between where you travel and any avalanche path. Slides may wrap around terrain features and surprise you and your group.

Reactivity of these persistent layers will increase as we get another load of precipitation and strong winds. To the east the main concern lies in triggering the whole snowpack to the ground. Further west, the main layer of concern is surface hoar that was buried on the 17th. You can find this most readily on sheltered but open, shaded slopes, above the valley floor. Look for shooting cracks, recent avalanches, and listen closely for whumphs. Lack of evidence in one profile or snowpack test shouldn't be a reason to travel in more consequential terrain.

 

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