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Avalanche Forecast

Archived

Jan 1st, 2019–Jan 3rd, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Snoqualmie Pass.

The bottom line: The avalanche danger is dropping, but you could still trigger avalanches on wind loaded slopes at upper elevations or on the eastern edge of the zone. If you plan on traveling in these areas, carefully choose terrain that minimizes your exposure to avalanches and use small test slopes to evaluate the snow. In adjacent zones to the north and east, observers have triggered dangerous avalanches on a layer of buried surface hoar near and above treeline.

Regional Synopsis

Happy New Year!

Thanks to all of you who volunteer, send observations, and support NWAC in various ways - we appreciate it.   

December of 2018 was fun (from a forecasting perspective) with three pronounced avalanche cycles, a couple different persistent weak layers, some rain events, and a flurry of human triggered avalanches to ring in the New Year. Most importantly, it seems that we made it through the last days of 2018 without anyone getting seriously hurt by an avalanche.

The deep (Dec 9) layer responsible for many of the avalanches early in the month no longer seems to be a problem in the western zones. That said, it is still possible to trigger an avalanche on its counterpart (or basal facets) in the eastern areas.

A widespread layer of surface hoar formed around Christmas. Late December storms preserved this layer in areas above the rain line and we have numerous (more than a dozen) reports of people triggering avalanches on it in the last three days. At least 4 people were caught and carried during this period, but so far we have no reports of serious injury. Most of these avalanches were soft slabs, D1-D2+, but there were several harder wind slabs in the mix.

It appears that the layer is most reactive and/or prevalent in the Crystal Mountain backcountry and in the mountains around Leavenworth and west of Mazama.

Surface Hoar can be an especially tricky and persistent weak layer. Read more about it here.

Weather Forecast

Weather Synopsis for Wednesday night through Friday

A Pacific front will spread increasing light precipitation to the Olympics and Mt Baker area Wednesday afternoon. The initial warm frontal moisture will be directed mainly across the north part of the forecast area overnight Wednesday. The heaviest precipitation will remain directed to the Mt Baker area Wednesday night, where it should become heavy.

Freezing levels rise rapidly overnight through early Thursday and peak Thursday morning along with continued heavy precipitation in the Mt Baker area with significantly less precipitation reaching the southern WA Cascades and Mt Hood area. 

Thursday should be a very wet day, especially in the north part with little to no precipitation reaching the Mt Hood area. 

Light easterly winds across the passes are not expected to save the Stevens and Snoqualmie areas from rain, as they often do throughout the winter. 

The associated cold front finally crosses the Cascade crest Thursday night, maintaining moderate to heavy precipitation and extending precipitation to the remainder of the forecast area in the south. 

Showers should continue to lowering freezing levels Friday as a weak upper trough passes the area. The Mt Baker area will continue to receive the greatest precipitation Friday, with gradually less towards the south.

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.