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RegisterApr 3rd, 2018–Apr 4th, 2018
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Several old weak snow layers exist in the snowpack east of the Cascade crest. We currently have very limited information concerning these persistent weak layers. You can avoid triggering a persistent slab avalanche by staying off of large open slopes greater than 35 degrees near and above treeline. If you are traveling near the Cascade crest, expect small shallow wind slab avalanches to have formed. Use visual clues such as fresh cornices, blowing snow, and snow drifts to identify and avoid wind loaded slopes.
Limited new snow totals expected Wednesday will not significantly increase avalanche danger in the Cascade East zones.
Several old weak layers of snow have been reported in the snowpack over the last several weeks. Recent weather conditions likely have not caused significant changes in these persistent weak layers. You are most likely to trigger a persistent slab on shaded aspects near and above treeline. While snow profiles and snowpack tests can demonstrate the presence of a persistent weak layer they cannot prove its absence. The best way to avoid triggering a persistent slab avalanche is to stay off of large steep opens slopes in locations where persistent slabs are thought to occur.
In some locations near the Cascade crest you may find small shallow wind slabs. If you see more than 6 inches of soft snow on the ground, expect wind slabs in nearby terrain. Use visual clues such as blowing snow, new cornices, and snow drifts to identify and avoid wind loaded slopes.
A lower elevations rain showers are likely to occur. Expect new rollerballs, pinwheels, and small loose wet avalanches if you experience rain while traveling. Stay off of slopes greater than 35 degrees if you observe prolonged or intense rain showers.
Around 2-4 inches (5-10cm) of new snow has fallen around the eastern zones in the Cascades. Locally higher snow totals may be found, particularly close to the Cascade crest. An observation on NWAC’s public observation page reported 6 inches (15cm) near Washington Pass. The new snow fell on a variety of snow surfaces including melt-freeze crusts, thin rain crusts, old wind textured snow, and settled soft snow.
Older layers of weak snow can be found in the snowpack. We have very limited information about the distribution and reactivity of these layers leading to a higher level of uncertainty. If you have any information or observations on layers within the snowpack please consider submitting them to NWAC via our public observations page. The exact weak layer and depth depends on your location. Several common weak layers are:
Other weak snowpacks may be found in locations further east of the Cascade crest or in areas where shallow snow exists.
Observations
North
On 3/23, professionals near Washington Pass reported 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 (3/22) on shaded aspects at variable depths within the two feet of the snowpack. Test results indicated the potential for propagation on both weak layers. Snow pits indicate a weakening 2/8 crust.