Avalanche Forecast

As we enter a storm cycle Thursday, human triggered avalanches will become increasingly likely as denser storm snow builds over weaker snow during the day. Storm slabs will likely become touchy by the end of the day. Watch for changing conditions, travel conservatively and rein in your plans if conditions deteriorate faster than expected. The avalanche danger is expected to further increase Thursday evening so plan your exit accordingly. See the mountain weather tab for weather forecast details. 

Watch for building wind slab on a variety of aspects Thursday, especially near and above treeline where there is plenty of low density snow available to transport onto lee slopes.  

There remains significant deep, soft snow out there from the past week. Unconsolidated snow, particularly around small trees, can present a non-avalanche, snow immersion hazard. Keep visual and verbal communication with your travel partners when traveling in treed terrain.

Also despite all this new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.

Our last major storm cycle ended 12/19-12/20. Since then a series of weak weather disturbances have traversed the area over the last week, depositing about 6-12 inches of low density snow. 

Periods of moderate and shifting winds have caused both wind stiffened surfaces and built wind slabs in exposed terrain near and above treeline. The few recent avalanches reported over the last week have involved wind slabs located in higher terrain and on steep features such as terrain convexities. 

The upper snowpack has been widely reported as well bonded to the December 15th interface. Where found, the December 15th layer varies from about 2-3 feet in depth throughout the west slopes of the Cascades. 

Observations

North

On Tuesday 12/26, NWAC Observer Lee Lazzara traveled between 2000-6000 feet in the Swamp Creek drainage. The recent cold low density storm snow from this past week has been preserved with a favorable and stable density profile near and below treeline. Snowpack tests failed to produce results within the upper snowpack and the 12/15 layer was not identifiable in this area. The wind slab problem in higher terrain was difficult to accurately assess due to  shallow new snow/low visibility. Wind slabs appeared to be the main current problem in exposed terrain and specific terrain features, such as slope convexities. Wind slabs were featured on a variety of aspects due to shifting wind patterns over the past week.

Central 

NWAC pro observer Jeremy Allyn was in the Source Lake area of the Alpental Valley Monday 12/26. Visibility was poor and no wind slab was directly observed in the terrain he traveled.  A thin crust formed by freezing fog was noted from valley floor up to 4900 ft.  

A skier on Humpback Mountain via the NWAC Observations page for Saturday 12/24 reported getting caught by a 2 ft wind slab on a west facing slope near the summit. No serious injuries were reported. Note that areas west of Snoqualmie typically have stronger winds during periods of offshore/easterly flow.

The Stevens pro patrol on Saturday found the 12/15 layer down 3 ft (85-90 cm) and unreactive in large column tests performed on north aspects. No wind slab was observed.

South

A professional in the Crystal backcountry Wednesday observed a settled snowpack well bonded to the 12/15 interface and no obvious layers of concern. 

A nice report via the NWAC Observations page from the Tatoosh on Saturday reported several triggered D1-1.5 loose dry avalanches on various steep slopes.