Avalanche Forecast

Following rain and freezing rain Saturday, 10-12 inches of snow accumulated Saturday night and Sunday with strong WNW winds. Winds shifted to easterly and transported snow to a variety of aspects making wind slabs possible on all aspects. Mt. Hood Pro-patrol found fresh but stubborn wind slabs up to 2' deep near treeline. More importantly, wind slabs had developed on unusual aspects, cross-loaded slopes and formed on open slopes below treeline. Winds had scoured ridges to the most recent firm icy crust in many areas. We have no recent observations from above treeline due to the recent stormy conditions.

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 Synopsis for Thursday night through Saturday

After raining cats and dogs at most sites along the west slopes of the Cascades this morning, a plume of warm frontal moisture has lifted north this afternoon, providing a break for the south Washington Cascades. However, the heavier precipitation and stronger winds will stay focused on the Olympics and Mt. Baker area through this evening. 

The associated frontal boundary will pass from north to south through the Cascades tonight and precipitation rates will pick up once again. Snow levels will be slow to cool, but a brief period of easterly flow may allow snow levels to briefly drop to Pass level early Friday morning.  Once the front passes through, snow levels will settle rather uniformly across the region in the 4000-4500 ft range.  

On Friday, the front will split apart as the parent low pressure system stalls off the central B.C. coast and a new upper low digs off the California coast. Post frontal SW flow should mainly benefit the Mt. Baker area in the way of significant accumulating snow showers above 4000 ft. Other areas will see light showers Friday. 

Showers should end Friday night with dry conditions forecast through Saturday morning.  An approaching longwave trough will begin to shift showers into the Olympics and south Washington Cascades and Mt. Hood on Saturday afternoon.