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Avalanche Forecast

Archived

Mar 5th, 2017–Mar 6th, 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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

The avalanche danger should gradually diminish Sunday, however dangerous avalanche conditions persist, especially near and above treeline.  Avoid steep slopes recently loaded with wind transported snow. Conservative decision-making remains essential.

Detailed Forecast

Light to moderate snow showers at cool temperatures are expected overnight and early Sunday before tapering through the day. Winds should be light, except light to moderate in the alpine.

Only light accumulations of new snow are expected and with cold temperatures and light winds this should not affect the current avalanche danger significantly. The avalanche danger should gradually decrease on Sunday. However, cold temperatures may help maintain older wind slab layers near and above treeline.

Careful snowpack evaluation and cautious routefinding will be essential at higher elevations Sunday.

Recent moderate to strong S-SW 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. Older wind slabs may be masked by shallow fresh snow.

Cornices won't be listed as an avalanche problem in this area, but avoid travel on ridges, where recent cornices may have formed and avoid slopes below cornices.

Snowpack Discussion

Weather and Snowpack

... Updated forecast to raise the danger level near and above treeeline in the Olympics due to the many recent triggered avalanches, Saturday March 4th.

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 carried a second stronger front across the Northwest on Friday evening. At Hurricane, 24 hour new snow of 8 inches were received as of Saturday morning, with about 12-14 inches since Thursday. The latest storm snow was received with 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 at Hurricane on Friday and found that ski tests were showing rapidly increasing propagation and increasing sensitivity of the deepening storm slab. Previous winds had loaded various slope aspects while south winds on Friday were loading N aspects.

...Updated  - From reports by NPS rangers early Sunday, there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday, March 4th. Including the areas known as Maggies, Hurricane Hill and Sunrise Face. This is indicating the recent storm snow remains sensitive to human trigger and more conservative decision-making remains essential until the storm and wind slabs settle further. 

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.