Archived

Avalanche Forecast

Jan 2nd, 2019–Jan 3rd, 2019

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Regions: Cascades - West.

The Bottom Line: A potent storm will bring strong wind and heavy snow to the highest elevations creating very dangerous avalanche conditions. Avoid steep slopes at upper elevations where the wind is drifting thick slabs. Stay out from under large avalanche paths that start 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.

Avalanche Problems

Wind Slabs

Heavy snowfall paired with strong and gusty winds will redistribute snow and build fresh wind slabs. Avalanches are very likely within wind-drifted snow at upper elevations. These avalanches will be large and could run far distances. Avalanches involving new snow have the potential to step down and trigger deeper weak layers in the snowpack. Watch for shooting cracks, collapses, and recent avalanches. Give the storm snow time to stabilize. Avoid travel in avalanche terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Very Likely

Expected Size: 2 - 2

Loose Wet

Expect wet loose avalanches on steep slopes at mid and low elevations. Avoid avalanche terrain during periods of heavy rain. As wet avalanches run downslope, they could entrain large amounts of snow and even trigger slab avalanches. Look for roller balls and pinwheels as indicators of weakening snow surfaces. Steer clear of gullies and other confined terrain features where debris could pile up and increase the consequences of even a small avalanche.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood: Likely

Expected Size: 2 - 2

Persistent Slabs

New snow and wind will thicken existing slabs resting on a layer of feathery surface hoar that formed around Christmas time. Observations from neighboring areas indicate the surface hoar has a spotty distribution and can be hard to find. Regardless, impressive and unusual recent avalanches still have us concerned. This layer can be found in the upper snowpack between 4500-5500ft primarily on north and east aspects. Be especially mindful of steep slopes near treeline that are sheltered from the wind. Let the snowpack adjust as it experiences rapid change over the next 24 hours.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 3