Avalanche Forecast
Regions: Olympics.
Mother Nature is throwing a lot of avalanche problems at us right now so review the forecast to remind yourself of what to watch for if you are planning a trip into the backcountry on Sunday. Re-evaluate or ratchet back your plans if you encounter significantly more new snow than described at higher elevations.
Detailed Forecast
A short break between frontal systems should be seen Sunday. Light showers mainly over the Cascade west slopes should taper off in the morning. Renewed light rain or snow should be seen mainly over the Olympics and northwest to central west Cascades as moisture from the warm front of the next system reaches the Northwest. Re-evaulate your plans if the weather is not turning out as expected.
Mother Nature is throwing a lot of avalanche problems at us right now so review the forecast to remind yourself of what to watch for if you are planning a trip into the backcountry.
New or previous wind slab should be suspected mainly on NW-SE aspects above treeline due to recent SW-W winds. But watch for firmer wind transported snow on all aspects especially in areas of complex terrain.
New sensitive storm slab is most likely above treeline in areas that receive more than a few inches of rapidly accumulating snowfall.
Avoid travel on ridges near where cornices will have been loaded and weakened by recent storms and avoid steep slopes below cornices that may fail at any time. Cornices have been reported as large and sensitive in several areas and have been involved in recent accidents and close calls.
Loose wet avalanches are most likely on solar slopes in the near and below treeline especially if you are in an area with sunshine or little cloud cover. Watch for surface wet snow deeper than a few inches, pinwheels and initial small releases that will get bigger the longer the sun heats the snowpack.
Dangerous avalanche conditions are expected Sunday. We only got a taste of the spring stabilizing process the past couple days. Avalanches may step down or entrain deeper layers and be large and dangerous especially if they reach the Valentine's Day crust layer.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. It looks like Hurricane had about 40-50 inches of snowfall.
A strong frontal system brought increasing precipitation and winds along with a warming trend to the Olympics and Cascades on Thursday. On Thursday night rain probably pushed up to about 5000 feet in the Olympics. By Friday morning Hurricane had about .5 inches of WE which looks like it fell as rain. This gave the snowpack a huge test and caused an avalanche cycle of several types of avalanches in the Olympics and Cascades.
Another front crossed the Olympics and Cascades on Saturday causing more SW-W winds, snow at higher elevations, and rain at low elevations. It looks like there is only some light amounts of new snow at Hurricane on Sunday morning.
Recent Observations
Reports by NPS rangers early Sunday 3/5 and a report listed on the NWAC Observations page indicates there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday 3/4, including the areas known as Maggies, Hurricane Hill and Sunrise Face.
The Hurricane rangers report that a snow boarder triggered a cornice release on Friday which in turn triggered a very large slab avalanche on the locally named Pit Bull path on a NE slope at about 5000 ft. A loose wet avalanche near the summit of Mt Angeles in turn triggered a large slab avalanche on S-SE slopes at about 6000 ft. Other loose wet avalanches from S-SE slopes crossed the main road below the level of Hurricane Ridge.
Goat Creek avalanche where it crossed the road at about 3500 ft. Photo by Dave Turner.
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2
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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1