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RegisterMar 30th, 2018–Mar 31st, 2018
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Heightened avalanche danger exists and you can trigger persistent slab avalanches, primarily near and above treeline on polar aspects. Watch out for steep roll-overs (convexities), unsupported features, and larger terrain of consequence. Warmer temperatures and sun are making it easier to trigger wet avalanches on steep, rocky, and sun exposed slopes. If you see recent roller balls, Loose Wet avalanches, or experience wet surface snow deeper than your ankle, move to shaded and drier slopes.
Heightened avalanche danger exists due to the potential for human-triggered large avalanches on Saturday.
You can trigger persistent slab avalanches on Saturday at upper elevations and on shaded aspects. Persistent Slabs are difficult to manage and can break in surprising ways. To stay safe, avoid where the problem exists or if you go there stick to lower angle slopes and limit your exposure to large avalanche paths. Snowpack tests can provide useful information, however they are not a decision making tool. If you see any cracking, experience collapses, or hear whumphs, stay off of nearby avalanche terrain.
The strong March sun is expected to be out in force on Saturday. Watch out for areas of unsupportive wet snow where Loose wet avalanches may occur. Plan your travel to minimize exposure to steeper slopes receiving significant sunshine. New rollerballs, new loose wet avalanches, or wet surface snow deeper than your ankle are all signs that a given slope may be unstable.
Warm sunny weather has created unsupportive wet snow at lower elevations and has allowed melt-freeze cycles to continue.
Rain and snow showers this week have been generally confined to areas near the Cascade crest. Snow levels hovered between 4500 and 5000 feet through much of the precipitation. Drier weather has prevailed in other areas of the Easter Cascade regions. Moderate winds transported soft snow at higher elevations likely forming wind slabs on lee slopes.
On slopes receiving direct sunshine expect new surface crust to have formed. The thickness of these new melt-freeze crusts depends on aspect and location within the region.
Below the surface snow, a high degree of variability can be found in the snowpacks east of the Cascade crest. Various melt-freeze crusts, strong rounded snow, and older weak snow layers may be observed.
A large amount of uncertainty exists regarding the distribution of two reactive buried surface hoar layers recently identified along the east slopes of the Cascades. These layers are possible to trigger and deserve careful snowpack evaluation. The weak layers were identified on N and N-NW aspects at 5900 ft on Dirtyface Mountain. If you gather additional information regarding these layers, please consider submitting an observation to NWAC.
Old persistent weak layers were involved in 3 avalanche fatalities over the past month. Many of these weak snow grain types have gained strength and rounded. The remaining weak layers are generally inactive or dormant. Drastic changes to the snowpack, such as significant amounts of new snow or a major rain event could make these layers a threat once again. Currently, the persistent weak layers that you may find include:
Other shallow and very weak areas of snowpack may be found further east of the crest or in areas with less snow.
Observations
North
On 3/23, professionals near Washington Pass reported a small skier triggered avalanche in the new snow on a steep east aspect at 6500 ft. The 3/8 buried surface hoar was reported as 1.5 feet (45cm) below the snow surface.
Central
On Friday, Matt Promomo was on Dirtyface Mountain where he found two buried surface hoar layers on shaded aspects at variable depths, depending on location, within the top meter of the snowpack. Test results indicated the potential for propagation on both weak layers. Snow pits indicate a weakening 2/8 crust.