Avalanche Forecast
Regions: Cascades - East.
The avalanche danger should decrease further on Monday. S-SE winds may distribute shallow amounts of recent snow onto lee aspects near and above treeline. Increasing clouds should lower the likelihood of small loose wet slides in the afternoon.
Detailed Forecast
Increasing cloud cover should quickly spread from south to north over the Cascades on Monday. Precipitation may develop for the southern Washington Cascades Monday afternoon but hold off until the evening for areas further north. Â Â
The avalanche danger should decrease further on Monday. Light to locally moderate S-SE winds may distribute shallow amounts of recent snow onto lee aspects near and above treeline. Older wind slab may linger on NW to SE aspects. Watch for firmer wind transported snow on all aspects, especially in areas of complex terrain.Â
Small storm slabs remain possible in specific areas on Monday especially near the Cascade crest for the central-east and northeast Cascades and mainly near and above treeline.Â
Increasing clouds should lower the likelihood of small loose wet slides Monday, however the avalanche danger will be maintained at Moderate Below Treeline for the northeast and central-east Cascades due to the potential to receive more solar radiation than areas further south. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases. Avoid areas with terrain traps where a small loose wet avalanche could have unintended consequences.Â
Expect regionally lower avalanche danger further from the Cascade crest and in the southeast Cascades Monday.Â
It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC and NRCS stations indicate about 2 feet of snow in the northeast Cascades with less elsewhere along the Cascade east slopes.Â
The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately these systems delivered more rain than snow. At least two regional avalanche cycles occurred during the stretch. The most recent cycle from earlier in the week had many massive slides that covered Hwy 20 near Washington Pass up to 40' deep in places! Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. Far less precipitation was seen further east of the crest during this period for areas like Blewett Pass and Mission Ridge.Â
After a short respite from the active weather pattern on Thursday, another strong low pressure system brought 6-12+ inches of snow to the northeast and central-east slopes of the Cascades Friday night and mostly rain for the southeast Cascades. This was followed by snow levels rising to 6000-6500 feet in the northeast and central-east Cascades and likely 7000 feet in the southeast Cascades by early Saturday morning. Rapid cooling began mid-day Saturday. Strong W-SW winds were likely transporting new snow above treeline by mid-day Saturday. Sunday was cool with light winds with a general clearing trend seen throughout the Cascades. Â
Recent Observations
North
The North Cascades Heli Guides were near Silver Star on Thursday 3/16 reported many previous natural storm slab avalanches up to size 3, likely releasing midweek. They also reported several small triggered storm slab avalanches. This activity was on N-NW slopes in the 8000 ft range.
More observations from Friday in this zone indicated a significant distinction in the recent storm snow with elevation, with up to 4 more inches of storm snow above about 6500 feet. The several recent warm precipitation events this week appear to have limited the upper elevations of rain to about 6500 feet. At elevations up to 8000 feet, the recent precipitation has fallen as snow. In these higher elevations, some shallow triggered storm slab avalanches have been noted over the past few days.
On Sunday, the NCH operation was in the Silver Star and Varden Creek drainages and found evidence of recent storm slab releases in unsupported steeper terrain mainly above treeline, but that recent storm slab was becoming less sensitive to human triggering. Â
Central
NWAC observer Jeff Ward was in the Cle Elum drainage on Mt Hawkins and Red Mountain up to about 6000 ft on Thursday 3/16 and noted evidence of an impressive avalanche cycle the past couple days. The current conditions were 3 cm of new snow over 3-7 cm thick, firm crust with recent rain penetration to about 40 cm in the snowpack. The Valentine's Day crust was found at 90 cm but tests did not give results.
NWAC observer Tom Curtis was at Blewett on Diamond Head up to about 5500 ft on on Thursday 3/16 where there were no recent avalanches just consolidation. SW-W-NW slopes were scoured, with a breakable or supportive crust elsewhere over moist 1F or P rounded crystals down to the ground. He found some reactivity in a layer at about 50 cm down, which should not be a current problem, but might have contributed to avalanches a week ago.
Mission Ridge pro-patrol reported a well-behaved spring-like snowpack in their area with no avalanche problems noted over the weekend.Â
South
No recent observations.Â
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
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: Possible
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: South East, South, South West, West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1