Avalanche Forecast

Cold temperatures with a chance of a few light snow showers Tuesday will not significantly improve the current avalanche danger, allowing recent slabs to persist longer than usual. 

Even a small triggered Loose-Dry avalanche or a small Wind Slab may be enough to trigger a Persistent Slab. Snowpack observations and one serious skier triggered avalanche from along the west slopes of the Cascades Sunday show you can still trigger dangerous Persistent Slab avalanches that are big enough to kill you on slopes steeper than about 35 degrees. Persistent Slabs can surprise even very experienced travelers and can break over terrain features. Put a wide buffer of terrain between where you travel and any steep slopes. Use extra caution in areas where avalanches could come down from above. Avalanches may be surprisingly large and run farther than you expect. 

The combination of Wind Slab and Persistent Slab requires very cautious decision-making and terrain selection. Persistent Slab avalanches are not very common in the Cascades and the usual playbook of waiting a day or two for storm instabilities to settle out does not apply.

Winds abated Monday but cold temperatures persisted, slowing the stabilization process of recent slabs.

Sunday saw light snow showers and much colder air move in along the east slopes of the Cascades. Moderate N-NE winds transported recent snowfall in the Washington Pass area and at Mission Ridge. Persistent slab avalanches were skier triggered near Harts Pass on small test slopes and identified in snowpack tests as likely to propagate. The distribution of the Persistent slab problem along the east slopes of the Cascades is unknown at this time. 

On Saturday, from the Hwy 2 corridor to the northeast Cascades up to 8 to 15 inches of snow fell. The snow level rose up to at least 4000' for the central-east zone Saturday afternoon; Blewett Pass mixed with rain while Mazama stayed all snow. Dirty Face and Mission Ridge stations reported very strong winds and although the Washington Pass station winds were not very strong, strong gusts were observed by professionals near Hart's Pass Saturday afternoon. 

In the Washington Pass area, approximately 14-25 inches of snow sit on the 2/5 crust. The crust likely extends up to around 6800’.  In some areas, the 2/5 crust sits over weaker snow (facets). 

A relatively well consolidated snowpack exists below the 2/5 crust. While we are tracking several older crust layers there are currently no other layers of concern in the snowpack.

In the last week of January, observers reported isolated buried surface hoar on top of the 1/16 crust. This persistent weak layer was found or thought to be the cause of several avalanches. A recent observation (2/11) from the Mission Ridge area confirmed this layer is still present in some locations. This layer will be worth tracking after Saturday's storm. Snow profiles and snowpack tests are the best means to confirm the presence of this layer.

Observations

North

NCH professionals in the Hart's Pass area Sunday found nearly 2 feet of snow failing on facets buried above the 2/5 crust. Snowpack tests and skier triggered avalanches on small test slopes indicated the potential for Persistent Slab avalanches in this zone. Wind slabs were sensitive to human triggering below ridges.  

A professional in the Hart's Pass area found deteriorating avalanche conditions Saturday as human and skier triggered slabs within the storm snow were reported by the afternoon. Winds became very strong and gusty in the afternoon along with the heavier snowfall. 

Central

NWAC Pro Observer Matt Promomo traveled in the Blewett Pass area Thursday. Matt found 1-3 inches of weak snow above the early February crust that had become faceted. No deeper persistent weak layers were identified in the lower snowpack. Winds had created variable snow surfaces above 5500 feet and snow depths averaged about 3 feet.