Avalanche Forecast

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.

Very light post-frontal showers decrease and generally end as SW flow continues behind a departed short-wave trough. Friday night with relatively mild with snow levels around 3000-4000 feet. A trough will approach from the SW as it digs into northern California, spreading some light precipitation into the Olympics in the early morning hours.

The main portion of the trough will move into the near-shore waters with light rain and snow brushing the coastline by the end of the day on Saturday.

Saturday night, the surface trough crosses the region, bringing a brief shot of strong westerly winds and moderate to locally heavy precipitation behind it, impacting Mt. Hood in the late evening and the Washington Cascades after midnight. At Snoqualmie Pass, precipitation will be a mix of rain and snow with east winds initially keeping temperatures cool, changing back to rain as the trough pushes westerly winds through and then rapid cooling changes precipitation back to snow behind the trough by Sunday morning. Snow shower activity appears initially poorly organized under the upper-level trough on Sunday with light to moderate winds.