Avalanche Forecast
Regions: Olympics.
A mixed bag of avalanche problems Thursday will keep heightened avalanche conditions in specific terrain. You can mitigate the loose wet and cornice risk by being aware of the terrain your connected with and by recognizing the rapidly increasing hazard in locations that warm quickly. Also, wind slabs may still be sensitive near and above treeline.
Detailed Forecast
Sunshine and moderating temperatures should be the story on Thursday. However, cool easterly winds should help offset some of the warming trend Thursday.
Still, mid-March sunshine will affect solar slopes by increasing the likelihood of loose wet avalanches on steeper solar aspects by quickly breaking down sun or melt-freeze crusts. While most loose wet avalanches should be small, they will have the ability to entrain recent moist snow in specific terrain. Recently formed cornices have grown large and should become more sensitive with warming and sunshine. You can mitigate the loose wet and cornice risk by being aware of the terrain your connected with and by recognizing the rapidly increasing hazard in locations that warm quickly.
Lingering wind slab will mostly likely be found on NW-SE facing slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab instabilities. Treat wind-loaded slopes in higher terrain with caution Thursday.
Snowpack Discussion
Weather and Snowpack
Storms have moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels. Two deep surface low-pressure systems moved across the Olympic Peninsula last week with the first passing last Thursday, March 10th and the next on Sunday, March 13th. These systems caused very stormy weather. Â
Cool and showery weather Monday and Tuesday with continuing moderate westerly winds deposited additional snow at lower snow levels. In the Hurricane Ridge area, about 2-3 feet or more of new snow has fallen since Thursday, March 10th.Â
Periods of strong to very strong winds during recent storms created widespread wind and storm slab problems, creating dangerous avalanche conditions. These recent storms have also built large cornices along ridges.
Daytime warming and settlement have allowed storm snow weak layers to settle and stabilize, therefore, storm slabs have been removed from the avalanche problem list.
The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
NWAC pro-observer Matt Schonwald toured around the Hurricane Ridge area Friday, March 11th. He found up to 20 cm of dense 1 F or P snow above the latest rain crust. Thin wind slab was generally not reactive except in isolated areas on N-NW lee aspects near treeline. Although cornices were large, they were generally firm and not sensitive. Windward slopes that had melted out a few weeks earlier had packed on a firm, and in places, icy thin cover. Overall Matt noted few current avalanche problems in the Hurricane Ridge area Friday, March 11th.
Recent storm snow instabilities should have settled out. The Olympics saw abundant sunshine for the first half of Wednesday which may have triggered a loose wet cycle on solar slopes before clouds increased in the afternoon.Â
Hurricane Weather Station
Internet communications to the station have been disrupted at the NWAC office. We have identified the problem and anticipate the station to return online sometime soon; we have an open trouble ticket with our internet provider and remain hopeful we will be back online shortly. We apologize for the outage and thank you for your patience. Â
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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
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: Possible
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, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1