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East Slopes South - South of I-90 to Columbia River

Issued: 6:00 PM PST Tuesday, January 2, 2018
by Dennis D'Amico

Shallow wind slabs may linger in wind exposed terrain near and above treeline while small loose wet avalanches are possible on steep solar slopes. In the Mission/Blewett area, be aware of the low likelihood of triggering a persistent slab in isolated areas on non-solar aspects above 5000'. You can dig snowpits to confirm the existence of depth hoar well before entering avalanche terrain and adjust your travel to respect this low likelihood/higher consequence problem. 

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Avalanche Problems for Wednesday

Wind Slabi

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Loose Weti

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Forecast for Wednesday:

After a cloudy start, partly to mostly sunny skies are expected Wednesday afternoon with continued mild temperatures. The exception once again will apply to the lower slopes where cooler temperatures and low clouds will persist due to temperature inversions. 

Lingering wind slabs should be far less sensitive to triggering on Wednesday and confined to higher terrain. Continue to watch for areas of recently wind transported snow such as fresh cornices, snow drifts, and uneven snow surfaces. Identify and avoid locations where recent wind loading occurred.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

Small loose wet avalanches are possible on steep solar slopes in areas that experience warm temperatures and afternoon sunshine on Wednesday. Be aware of the consequence of even a small loose wet avalanche around terrain traps.  

In the Mission/Blewett area, be aware of the low likelihood of triggering a persistent slab in isolated areas on non-solar aspects above 5000'. Varied surface roughness combined with an overall shallow snowpack made for a low likelihood of finding the right terrain to support a persistent slab avalanche. However, you can dig snowpits to confirm the existence of depth hoar well before entering avalanche terrain and adjust your travel to respect this low likelihood/higher consequence problem.

Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

Avalanche Summary:

Cool weather east of the Cascades has slowed the stabilization of wind slabs formed during the recent active weather pattern. However, on Monday and to a lesser extent on Tuesday, warmer air finally worked it's way aloft, with higher elevation stations such as Lyman Lake, Mission Ridge and Dirty Face warming near or above freezing while lower elevations stayed in the freezer (see graph below).

 

Winds toward the end of the last storm cycle in late December formed firm and initially reactive wind slabs on a variety of aspects.

Storm totals from across the east slopes of the Cascades show 1 to 2 feet of snow (highest storm totals Lake Wentachee and Holden area) fell during the series of storms ending Saturday Dec. 30th. 

Snowdepth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger. 

Observations

North

North Cascade Mountain Guides were in the Washington Pass area Friday through Sunday. By Sunday, sensitive storm slab layers were gaining strength and becoming unlikely to trigger.  Wind slabs were thought to be stubborn but were still avoided or approached cautiously above treeline. One natural cornice release was observed on Sunday. 

Central

A NWAC forecaster was in the Diamond Head area of Blewett Pass on Tuesday and traveled on non-solar aspects up to 5800 feet. Depth hoar was rounding but present above 5000' on NW-N-E aspects. Large column tests showed the 2 ft (60 cm) slab above this layer was reactive and likely to propagate. However, varied surface roughness combined with an overall shallow snowpack made for a low likelihood of finding the right terrain to support an avalanche. Just like the nearby Mission Ridge area, this layer will need to be watched moving forward.  Other pertinent observations from the area include a rain crust observed up to 5400 feet. Snowdepths were quite low in this area, making backcountry travel difficult at lower elevations, wind scoured areas and on solar aspects. 

Mission Ridge Pro Patrol reported very sensitive wind slabs observed around the area Saturday. A natural avalanche cycle was observed from Friday night. Avalanche control work within the ski area Saturday produces 1-4 ft wind slab avalanches. The larger avalanches released to ground on 1 mm basal facets.

South

No recent observations

No Corresponding Mountain Weather Forecast Available
This information is provided by the U.S.D.A. Forest Service and describes general backcountry avalanche hazard and conditions. It does not apply to ski areas and highways where avalanche mitigation is conducted. Read more here.