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Avalanche Forecast

Archived

Dec 3rd, 2017–Dec 4th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features. 

Detailed Forecast

More sunny weather should be seen on Monday with light northwest winds.

Recent snow layers will continue to stabilize at Hurricane Ridge. 

Small wind slabs lingering mainly on NW through E aspects will be the main concern on Monday. These wind slabs are expected to be stubborn or difficult to trigger. Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features.

The light amounts of 24 snow ending Sunday morning and the stabilizing process will be starting to limit the potential for storm slab. 

Continue to watch for isolated, small, triggered loose dry avalanches on steep terrain on non-solar slopes on Monday.

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

Warm, wet weather before Thanksgiving caused wet snow and glide avalanches as well as significant snowpack consolidation. There are no snowpack concerns below the Thanksgiving crust and in general new snow received post-Thanksgiving has reportedly bonded well.

A series of frontal systems produced snow over the past week since the Thanksgiving warm period: Hurricane Ridge received about 2' of snow.

This includes the recent snow accumulation for the 48 hours ending on December 3 at Hurricane Ridge of about 10".

Since last Monday, temperatures at Hurricane Ridge have been generally steady in the upper 20's and winds have been mostly southerly in the single digits and teens.

On Sunday winds have shifted to light northerly.

Observations

Friday morning: NPS rangers reported 5" of new snow along with active wind transport of the new snow. 

Saturday morning: NPS rangers report 7" of new snow. Small, 15 cm deep natural storm slab avalanches were being triggered by tree bombs along the road. Snow pit tests on a north slope at 5200' gave ECTP2 and ECTP4 @ 10 and 15 cm, respectively. Clean propagation was observed in both cases. On this test slope, the pencil hard Thanksgiving rain crust was down 55 cm.

On Sunday morning, the Hurricane Ridge rangers report small, loose dry avalanches along the road with no slab character. Ski penetration was 6" with generally right-side-up near surface snow.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.