Avalanche Forecast

Remote triggered slab avalanche on 12/31/18 in the Icicle Creek area in the adjacent zone to the north.  Numerous similar avalanches were seen releasing on buried surface hoar averaging about 14 inches down. Photo: Matt Primomo 

The snowpack on the eastern slope is highly variable. In some places, it is fairly strong and supportable but has a layer of facets near the ground that warrants patience and respect. In others, it is shallow, weak, and may not support the weight of a snowmobile or a person very well.

Large avalanches remain possible within old, faceted layers near the ground. Persistent slabs are often very difficult to predict because you may not get direct signs of instability with these deeper layers. What we do know is that after a significant loading event, persistent slabs often become easier to trigger. The snowpack needs time to adjust to the new load.

Reduce the risk of this high consequence situation by avoiding particular types of steep slopes. Things to look out for are wind stiffened slabs, and where they may overly shallow, rocky areas near and above treeline. Avoid steep, unsupported slopes with recent wind loading. Don’t underestimate how far and wide a slab failing in old snow could run when identifying safer areas to stop and regroup. Be intentional about putting a significant distance in between yourself, and where avalanches start, run, and stop.

We have no direct snowpack or avalanche observations from this area, but the conditions described have been seen in the adjacent zone to the north. Take the time to evaluate conditions for yourself before entering avalanche terrain.

Forecast Schedule and No Rating

At this time, we do not have enough specific snowpack information to issue an avalanche hazard rating for the East Slopes South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season. When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.

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.