Avalanche Forecast
Regions: Olympics.
Despite the continued slow stabilizing trend, specific terrain still has the potential to produce large and destructive avalanches. There is still a chance that you could trigger a large Persistent Slab avalanche. This problem is difficult to manage and can break widely, but you can reduce your risk by avoiding open slopes 35 degrees and steeper.
Detailed Forecast
Although it is becoming unlikely, you may still be able to trigger Persistent Slab avalanches on slopes 35 degrees and steeper. We think this problem is decreasing in the Olympics because we have no reports of recent avalanche activity. Facets (weak snow) have not been found to be widespread. However, variability exists across the terrain and persistent slabs have proven to be quite dangerous in the nearby Cascades so reduce your risk by avoiding steep, open slopes and large avalanche path and dig down and check for weak sugar-like facets or buried surface hoar above the most recent firm crust layer formed in early February on all but south aspects before engaging with avalanche terrain. This crust layer is down about 2-4 feet.Â
Small loose wet avalanches are possible on Wednesday on steep solar slopes and below treeline. Avoid steep sunny slopes near terrain traps if the surface snow becomes moist and watch for signs of natural pinwheeling and rollerballing as a clear signal to change aspects.Â
Snowpack Discussion
No recent avalanches have been reported from the Olympics.
Tuesday was mostly sunny with freezing levels rising to around 5000'. Monday's mostly cloudy skies followed light snowfall on Sunday afternoon, bringing 2-3" of new snow with light winds. Up to 2 feet of snow fell near Hurricane Ridge at the end of February. Winds as recent as Thursday formed Wind Slabs on a variety of aspects near and above treeline. In sheltered areas generally soft unconsolidated surface snow exists. Large snowdepth differences exist between shallow southerly and deeper northerly aspects.Â
On shaded aspects, about 3 ft of of settled snow sits on top of the weak persistent grains (see observation below) that formed on a strong crust earlier in February that should be healing with time. No recent snowpack tests have been reported on this layer. On these aspects, there are no other significant layers of concern in the mid and lower snowpack.
A very different and very shallow snowpack exists on south-facing aspects where warm temperatures and sunshine prior to mid-February melted the majority of the snowpack. Much of the snow on south-facing was deposited from mid-February onwards. Basel facets were present on the ground and this will be something to watch if warm temperatures don't round these grains before the next snowfall.
Observations
On Saturday March 3rd, NPS rangers found 2-3 mm buried surface hoar from mid February intact on a NNW aspect at 4990’. The surface hoar was about 4" (10 cm) above a crust 32" (80 cm) below the surface. No new or recent avalanche activity was observed on this layer. The snow depth was much shallower on due south slopes (as little as 1.5 ft deep, recent snow only) as compared to northerly slopes (120" deep). On south-facing aspects, the total snow was 1.5' deep and 1-2 mm basal facets were present on the ground.
On Friday, March 2nd, NPS rangers reported a large avalanche on a recently wind loaded slope. Elsewhere, profiles showed a faceted weak layer buried in mid- February was found 2-4 feet below the surface and was showing some signs of rounding.
Avalanche Problems
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1