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Avalanche Forecast

Archived

Mar 17th, 2015–Mar 18th, 2015

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

Regions

Stevens Pass.

Winter returned briefly to the Cascades over the weekend, but the mid March sun's strength can rapidly create locally dangerous conditions on steeper solar slopes, where even a shallow and slow moving avalanche could be powerful and could force you into unintended terrain traps. Also, watch for weakening cornices along ridges during the warmer part of the day.

Detailed Forecast

A weak weather system should cause a few showers overnight Tuesday and early Wednesday, but only very light amounts of rain or snow are expected and this should not cause an increased danger. Gradual clearing later Wednesday and some sunshine should lead to warming and increase the chance of small loose-wet avalanches. 

Lighter snow accumulations along with ample terrain anchors should greatly limit the avalanche danger below treeline. 

Remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). Significant new snowfall was received near and above these elevations on the volcanoes over the weekend and likely poses a higher avalanche hazard.  

Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow to cause an avalanche danger.

Snowpack Discussion

Over the weekend, another warm and wet system in SW flow brought a one-two punch to the Pacific Northwest. The initial system Saturday brought 1.5 - 2.5 inches of rain with the snow line around 6000-7000 ft. On Sunday, a second low pressure system deposited about 8-16 inches above 6000 feet in the south Cascades and 4500 feet in the north Cascades by early Monday. Significantly lesser amounts of new snow were received below these elevations.   

NWAC observer Dallas Glass was at Paradise Sunday and observed a climber trigger a loose wet avalanche, size 2, on a steep slope at 6500 ft near treeline (no injuries). He found skier triggered moist storm slabs and loose wet avalanches were possible in the near treeline band involving the 8 inches (20 cm) of new storm snow.

Observations in the Mt Baker and Chinook Pass area Monday revealed some storm slab, natural avalanches that had released likely during the Sunday storm cycle. In the Mt Baker area Monday, sunshine and daytime warming helped storm snow settle and become more slab like, leading to a few shallow releases by midday. 

By Tuesday, settlement and thin crust formation had reduced slab release likelihood shifting the problem mainly to loose-wet slides.  

 

Evidence, Monday, March 16th of storm avalanche activity Sunday on Naches Peak, photo J. Stimberis

The snowpack at low elevations remains meager to non-existent with the average snow-line around 4500 ft along the west slopes. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.