Avalanche Forecast

Continued warm temperatures and sunny weather will maintain dangerous avalanche conditions Monday.  

You will be able to trigger wet snow avalanches Monday as warm temperatures and sunny skies create wet snow conditions. However, E-SE winds will locally cool the snow surface at higher elevations near the Cascade crest, creating a more variable loose wet problem than Sunday. Expect new rollerballs, pinwheels, and loose wet avalanches to occur. These conditions will develop first on steep rocky slopes receiving direct sunshine and especially on wind sheltered slopes. Unstable wet snow will spread to other aspects as the day warms. As water reaches deeper weak layers in the snowpack, wet slab avalanches may occur. If you see any evidence of new wet slab avalanches dial 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 along the East slopes 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 weekend (3/3-3/4). 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 heating and the sun.

Sunny skies and mild temps Saturday and Sunday 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. Strong winds transported snow forming wind slabs and other wind-affected snow surfaces. This resulted in several wind slab avalanches being reported from the Washington Pass area Friday and Saturday. 

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 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.