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Avalanche Forecast

Archived

Mar 3rd, 2017–Mar 4th, 2017

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

Regions

Olympics.

The avalanche danger should decrease on Saturday but the decrease will be a moving target and careful snowpack evaluation and cautious routefinding will be essential.

Detailed Forecast

Decreasing winds and mostly light snow showers should be seen over the Olympics on Saturday with much lower snow levels and much cooler temperatures. Not a lot of snow is expected following the front Friday but we will see how it goes. The avalanche danger should decrease on Saturday but the decrease will be a moving target and careful snowpack evaluation and cautious routefinding will be essential.

Layers of recent or new wind and storm slab may need a day to mostly stabilize. Water may also need a day to drain from the upper snow pack below about 3-4000 feet.

Recent moderate to strong southwest to west winds will make wind slab most likely on northwest to southeast slopes but keep an eye out on all aspects in areas of more complex terrain. Watch for firmer wind transported snow from Friday and possible deeper wind transported layers such as from Tuesday.

New storm slab formed on Friday may need a day to mostly stabilize on Saturday. Storm slab is most likely in area that experienced more than a few hours of rapidly accumulating snow.

Cornices won't be listed as an avalanche problem in this area but avoid areas on ridges and mountain tops were a cornice might be present and avoid slopes below cornices.

Snowpack Discussion

Weather and Snowpack

The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost, very strong rain crust in the snowpack. 

A series of disturbances in cool, NW flow aloft from Saturday 2/25 through Tuesday 2/28 deposited about 10 inches of snow at Hurricane. Very strong alpine winds were seen in most of the Olympics and Cascades on Tuesday.

Southwest flow aloft began to ramp up again on Thursday as the first in a new series of fronts crossed the Northwest. Strong southwest flow is carrying a second stronger front across the Northwest on Friday evening. At Hurricane this will be causing strong SSW alpine winds and moist, dense new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft.

Recent Observations

NWAC observer Matt Schonwald was Hurricane on Friday and found that ski tests were showing rapidly increasing propagation and increasing sensitivity of deepening storm slab. Previous winds had loaded various slope aspects while south winds on Friday were loading N aspects. 

Problems

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.

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.