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Avalanche Forecast

Archived

Jan 17th, 2015–Jan 18th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Snoqualmie Pass.

Sunday should be fairly stormy day west of the crest. New storm and wind slab layers are likely.

Detailed Forecast

A wet cold front will cross the Northwest Saturday night. Snow levels will be highest on Saturday night. A good period of southwest-west flow, moderate to heavy orographic snow showers, and cooling with lowering snow levels should be seen on Sunday. New snow by the end of the day Sunday west of the crest should vary a lot from lower to higher elevations with a foot or more at higher elevations.

Building storm slab is likely mainly near and above treeline on Sunday. Watch for cracking and releases on steep sheltered slopes where snowfall exceeds an inch an hour for more than a few hours.

Building wind slab is also likely mainly near and above treeline on Sunday. Watch for firmer wind transported snow on lee slopes.

The freezing rain crust at Snoqualmie may act as a bed surface in that area.

The cooling should cause some good snow conditions on other slopes. Don't let powder starvation change plans to stick to safe slopes on Sunday. It is always a good plan to give new snow layers a day to stabilize before venturing to steeper slopes after a storm.

Snowpack Discussion

A front late Thursday was followed by showers Friday. West of the crest this gave up to about 10 inches of storm snow.

Some natural storm slab avalanches were reported in the Mt Baker backcountry. The avalanches released on north aspects at 5000 feet, about size R2, small relative to paths.

NWAC observer Dallas Glass and the Alpental patrol report a freezing rain crust on the surface at Snoqualmie on Thursday and Friday which may act as a bed surface in that area Sunday.

The underlying mid and lower snowpack west of the crest mainly consists of melt-freeze crusts and stabilized rounded grain layers. This is due in great part to the warm and dry period from about 6-15 January and previous similar periods so far this winter. Persistent weak layers are not expected west of the crest.

The overall snowpack remains well below normal for this time of year and some windward or southerly aspects have little if any snow cover.

 

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.