Avalanche Forecast
Regions: Olympics.
Warm and sunny weather will continue to cause wet snow conditions Monday in the Olympics. Avoid slopes where even small avalanches may have large consequences such as above cliffs, creeks, and rocks. Weak older snow exists in the snowpack. This is a classic low likelihood-high consequence scenario. To avoid large persistent slabs, stay off of steep large open slopes that may still harbor this difficult to predict and manage avalanche problem.
Detailed Forecast
Wet snow will develop with continued sunshine and warm air temperatures creating conditions for wet avalanches. This will happen first on steep rocky slopes receiving direct sun but will spread to all aspects as air temperatures warm. A poor overnight refreeze will allow this process to occur faster on Monday. Stay away from slopes where even a small loose wet avalanche may have higher consequences such as above cliffs, gullies, and creeks.
Several deeper persistent weak layers have been reported in the snowpack. The exact weak layer and depth depends on your aspect and elevation. This can be a classic low likelihood-high consequence scenario. To avoid persistent slabs, stay off of large open slopes where these larger avalanches may occur. While they are difficult for a person to trigger, a small avalanche such as a loose wet or cornice fall may trigger these deeper layers.Â
Limit your exposure to overhead cornices as you travel. They could fail without warming due to daytime warming and sunshine.
Snowpack Discussion
Temperatures gradually warmed over the weekend, topping out in the mid-40s at Hurricane Ridge Sunday afternoon.Â
Three to four inches of snow fell in the Olympics Thursday night into Friday. Winds during the storm redistributed the new snow on exposed areas near and above treeline. This soft snow is the most susceptible to impact by warm temperatures and sunshine.
Older weak snow layers continue to be reported in the Olympics. On slopes that receive direct sun, several facet/crust layers may be found. A more widespread layer of weak sugary facets was found just above a very firm melt-freeze (2/8) crust formed in early February. The depth to this weak layer depends on aspect and elevation.
We have not received reports of recent avalanches in the Olympics other than small wet loose on steep sunny slopes.
There are no significant layers of concern below the 2/8 crust layer.
Observations
On Sunday as of 1 PM, NPS rangers reported generally small loose wet avalanches with one larger release caused by a partial cornice collapse.Â
On Saturday, Forecaster Robert Hahn and NPS Rangers found the 2/8 weak snow/crust interface in snowpits on a West aspect at 5300' and down 2.5 feet from the surface. No new avalanche activity was observed other than small wet loose avalanches on steep sunny slopes. North facing terrain still held drier settled powder.Â
On Wednesday March 7th, a NPS ranger traveled in the Victor Pass area and found many crusts with facets forming on south aspects. Near ridge-tops, the 2/13 weak layer was 8-12" down and 3 mm facets were observed. Mid-slope this layer was down 3-4 feet.
Avalanche Problems
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: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
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.
Elevations: Treeline, Below Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1