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Avalanche Forecast

Archived

Mar 4th, 2015–Mar 5th, 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

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It is getting to be the time of year when you often need to watch for both winter and spring types of avalanche conditions. It is always good to read the forecast for details.

Detailed Forecast

Light winds and mid or high clouds should be seen on Thursday. The most clouds will be seen over the Olympics and north Cascades.

It is hard to say how much of a problem loose wet avalanches might be on Thursday. Watch for wet snow deeper than a few inches or rollerballs or pinwheels on steep solar slopes. The problem of loose wet avalanches should not be extensive but limit your terrain choices if you see more activity than expected.

Small areas or pockets of wind transported snow from last Friday and Saturday is most likely to linger on unusual south to northwest facing slopes on Thursday. This should be most likely in the Snoqualmie to Mt Rainier area where there was the most recent snow. But on most slopes the sunny weather will have caused these layers to bond and merge with underlying layers and it should no longer be a problem.

Cornices will not be listed as a problem yet but start to practice checking the ridges for these as we shift into spring.

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 (new or existing) to pose an avalanche hazard.

Snowpack Discussion

The last snowfall in the Cascades was late last week when about 8-13 inches fell near and above treeline west of the crest from Snoqualmie to Mt Rainier with less elsewhere along the west slopes.

This was followed by local strong northeast winds in the Cascades Friday and Saturday.

NWAC pro-observer Jeremy Allyn was at Paradise on Friday and found 10 inches of new snow, By mid-day the northeast winds were causing transport and fresh wind slabs on west aspects. See his video on the NWAC Instagram account. The Crystal ski patrol also reported a small 1.5 foot skier triggered wind slab on Saturday due to cross loading at 6850 feet. 

NWAC pro-observer Jeff Hambelton was at Mt Baker on Saturday here there was less recent snow and reported no evidence of instability near and below treeline.

Jeremy Allynn was back out at Crystal Sunday and reported many skiers and no avalanches. A report via Turns All Year for Mt St Helens Sunday reported wind slab but no sign of propagation and they did not tempt steeper slopes.

Minor cooler weather on Sunday and Monday has been followed by sunny and gradually weather on Tuesday and Wednesday. This should have have mostly stabilized the recent wind slab layers.

The mid and lower snowpack west of the crest snow 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.

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.