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Avalanche Forecast

Archived

Feb 3rd, 2017–Feb 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Natural or triggered wind and storm slab avalanches are likely at Hurricane on Saturday. Rain at the lower elevations may also trigger loose wet or wet slab avalanches on Saturday. Careful snowpack evaluation, cautious routefinding  and conservative decision making will be essential at Hurricane on Saturday.

Detailed Forecast

A very important pattern change is taking place over the Northwest Friday and Saturday. The dry weather and strong cold E-NE winds seen Wednesday and Thursday are being replaced by increasing strong southwest flow aloft, increasing snow and warmer temperatures Friday and Saturday.

Saturday over the Olympics should be a day of strong southwest alpine winds, moderate to heavy snow with snow changing to rain at lower elevations, and warming temperatures. But less snow will be seen at Hurricane where perhaps 6-8 inches of new snow is likely by the end of daylight hours on Saturday.

At Hurricane this will generally build new upside down wind and storm slab layers. New sensitive wind slab is likely on NW to SE slopes.

Wind slab formed by strong E-NE winds on Wednesday and Thursday may linger on Saturday. The primary aspects for these wind slabs should be W facing slopes.

New sensitive storm slab should continue to build at Hurricane on sheltered slopes on Saturday in areas that see rapidly accumulating snow. The warming trend will help build upside down layers and promote storm slab formation.

Rain at the lower elevations may also trigger loose wet or wet slab avalanches on Saturday. 

Careful snowpack evaluation, cautious routefinding  and conservative decision making will be essential at Hurricane on Saturday.

Snowpack Discussion

Weather and Snowpack

An atmospheric river arrived over the Northwest Tuesday 1/17 with heavy rain seen up to at least 6000 feet in the Hurricane Ridge area.

A storm cycle from Thursday 1/19 through Sunday, 1/22 deposited about 2 feet of snow at Hurricane Ridge.

A large upper ridge and warm air mass built over the Northwest Thursday through Saturday 1/26-1/28. Temperatures warmed into the 40s at Hurricane Ridge.

Strong NE-E winds have been seen Wednesday and Thursday with very cold temperatures.

Recent Observations

A skier was caught and carried by a wind slab avalanche on the back side of Maggies Saturday 1/28. A report with a well done video is available on the NWAC Observations page.

Another report received on Saturday 1/28 from the Obstruction Point road area via the NWAC Observations page indicated windy and warm conditions, with pinwheels, roller balls and surface crusts on W-SW slopes.

NWAC pro-observer Matt Schonwald was at Hurricane on Friday and found scoured slopes or shallow new snow on E slopes and shallow building wind slab on SW slopes. He found no significant signs of instability, ski tracks still visible from last week and lots of surface roughness to fill in on lee slopes.

 

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.