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Avalanche Forecast

Archived

Jan 22nd, 2017–Jan 23rd, 2017

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

Regions

Olympics.

Watch for new wind slabs formed Sunday on exposed lee slopes, especially near and above treeline. Wind slabs are most likely on NE-W-SW aspects. Storm slabs should continue to slowly stabilize Monday. Watch for wet snow avalanches on steep solar aspects if the sun comes out in the afternoon.

Detailed Forecast

Mostly cloudy early Monday with a chance of a few light snow showers, light winds with cool temperatures. Clouds should decrease becoming partly cloudy late Monday.

These conditions should allow for a gradual decrease in avalanche danger as recent wind and storm slabs begin to settle and stabilize. 

Allow existing storm and recent wind slabs time to continue stabilizing on Monday. Wind slabs are most likely on NE-W-SW aspects due to recent and expected SE transport winds. Look for recent wind effects near and below ridgelines and treat wind loaded slopes with caution.  

Storm slabs should continue to stabilize Monday. Wind and storm slabs may extend into the upper portion of the below treeline band, but the overall avalanche danger will be rated as low.

Snowpack Discussion

Weather and Snowpack

An arctic air mass was over the Northwest with fair, cold weather last week. Surface hoar and near surface faceted crystals formed in wind and sun-sheltered areas during this period. Recent observations on Thursday, Friday and helped confirm that we aren't dealing with any older layers formed during this period.  

An atmospheric river moved over the Northwest Tuesday and Wednesday. Heavy rain was seen up to about 5500 feet in the Hurricane Ridge area. 3 day precipitation totals through noon Thursday were about 2.5 inches at Hurricane Ridge. An avalanche cycle likely occurred in the Olympics during this period.

The NPS reported a storm total of 15 inches of lower density snow at the Hurricane Ridge manual snow plot Thursday morning. Showers continued during the day Thursday, but our precipitation gage didn't record any precipitation after 9 am, possibly due to equipment problems. About a foot of snow fell at the Waterhole NRCS Snotel over a 24 hour period ending Friday morning. 

A very pleasant day Saturday allowed temperatures at Hurricane to reach the freezing mark. Showers late Saturday and another band Sunday, deposited about 4-6 inches of new snow as of Sunday afternoon at Hurricane, with strong S-SE winds.

Recent Observations

NPS personnel reported debris in the Old Faithful track down to the Hurricane Ridge road at 3500 feet. Debris piled up 10-15 feet deep in this narrow slide path. Plow drivers discovered the debris midday Wednesday with the avalanche likely occurring Tuesday or Tuesday night. 

Pro-observer, Matt Schonwald, was at Hurricane Ridge Friday. Matt found 10" (25 cm) of settled recent storm snow generally well bonded to the underlying rain crust and not reactive. SE winds were forming shallow wind slabs on lee slopes near treeline. The recent rainfall had penetrated well into the snowpack. At a limited number of test sites, the 12/17 PWL was found to be rounding and unreactive in snowpit test and well over a meter down. We feel comfortable removing the persistent slab from the avalanche problem list moving forward. 

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.