Avalanche Forecast

You will be able to trigger wet snow avalanches Sunday as warming air temperatures and sunny skies create wet surface snow. These conditions will develop first on steep rocky slopes recieiving direct sunshine. Expect new roller balls, pinwheels, and loose wet avalanches to occur. Unstable snow will spread as air temperatures warm, effecting even shaded slopes. Stay off of any steep slope where you see wet surface snow. As water reaches deeper layers in the snowpack, wet slab avalanches may occur. If you see any signs of new wet slab avalanches, step back your terrain use, and avoid all avalanche terrain.

You are most likely to find and trigger lingering wind slabs on shaded slopes near and above treeline where wind deposited snow Thursday and Friday. Use visual clues such as fresh cornices and snow drifts to identify and avoid wind loaded slopes.

Persistent slabs continue to exist in along the eastern regions of the Cascades. The exact depth and type of persistent weak layer depends on location. These present a low likelihood-high consequence scenario that resulted in three fatalities last week. Just because you see tracks on a slope does not mean it is safe. To avoid persistent slabs, stay off of large open slopes where these larger avalanches may occur. While these avalanches may be difficult for a person to trigger, a small avalanche such as a loose wet or cornice fall may trigger these deeper layers.

Limit your exposure to overhead cornices as you travel. They may fail without warning due to daytime warming and sunshine threatening slopes below.

Sunny skies and mild temps Saturday allowed the sun to effect surface snow on sun exposed aspects. Cold snow likely remained on shaded slopes.

Generally 6-14" of new snow fell along the east slopes of the Cascades Thursday through Thursday night, with lesser amounts further east. Winds heavily transported the snow forming wind slabs and other wind-affected snow surfaces. This resulted in several wind slab avalanches being reported from the Washington Pass area in the last two days.

Weak persistent layers exist within the snowpack. In the past two weeks three avalanche fatalities have occurred because of persistent slabs. The exact persistent weak layer and depth is dependent on location.

Three commonly seen persistent weak layers are:

• Surface hoar and facets buried on 3/8. This layer is generally found near and below treeline just below the recent strom snow.
• On slopes that received direct sun, a thin facet-sun crust can be found. This layer is generally 1-2 feet below the snow surface.
• A more wide spread persistent weak layer is found just above a firm crust layer buried on 2/5. This layer of weak sugary facets (2/13) can be found 2-4 feet below the snow surface.
• Other shallow and very weak snowpacks may be found further east of the crest or in areas with less snow.

Observations

North

On Friday and Saturday, North Cascade Heli reported several slab avalanches near and above treeline. These avalanches occurred on a variety of aspects and were up to size D2.

On Thursday, North Cascades Heli reported a D1.5 (small/large) avalanche that occurred naturally where a wind slab relased on a 40 degree SE aspect at 6800 feet near Washington Pass.

On Thursday during the storm, NCMG generally found the 2/5 crust down 30-35" in the Hairpin valley with a 0.5 cm layer of 1.5 mm rounding facets. They did not see the Feb 23 facets, but found a layer of 5 mm surface hoar buried on March 8th down 3-12" due to variable wind transport. Wind slabs were reactive on N-E-S aspects. 

Mid-week, observers reported a mix of sun crusts and surface hoar/near surface facets prior to snow on 3/8.

Central

On Friday, Mission Ridge Pro Patrol reported 2" of new snow with extremely high winds forming slabs that were not reactive on test slopes or column tests. The recent 2" of snow sits on a layer of 3-4 mm surface hoar buried 3/8. The 2/5 crust was down 20" and was still reactive in snowpack tests.