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Avalanche Forecast

Archived

Feb 17th, 2017–Feb 18th, 2017

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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Recent wind and storm slabs will continue to gain strength Saturday. Continued caution is recommended in steep open terrain near and above treeline. Watch for wet snow conditions at lower elevations.

Detailed Forecast

In the northeast zone, light winds and a few light snow showers should continue to decrease the current avalanche danger. Any recent wind and storm slabs should continue to slowly settle and stabilize. 

Watch for any wet snow conditions at lower elevations, especially on steep unsupported terrain features.

Continue to be cautious Saturday in steep, recently wind loaded terrain, mainly near and above treeline below ridges. 

 

Snowpack Discussion

Weather and Snowpack

High pressure Saturday to Tuesday brought increasing sunshine and warming temperatures. Temperatures reached the 30's and 40's in many areas along the Cascade east slopes. This caused snowpack settlement, some small loose wet avalanche activity and left a melt-freeze crust in many areas.

Yet another atmospheric river arrived across the PNW beginning on Wednesday.  Light to moderate snow with warmer temperatures and some high snow levels occurred along the east slopes of the Cascades with localized freezing rain along the lower east slopes. Above freezing temperatures occurred during precipitation with light rain likely in the southeast zone up to 7000 feet, 5000-6000 feet in the central-east and reports from the north-east zone of a thin freezing-rain crust to near treeline elevations at least. 

The NWAC station at Washington Pass received about 1.25 inches of water equivalent by Thursday morning, 2/16, resulting in about 10-14 inches of moist snow over a melt-freeze crust.   

Recent Observations

North

NWAC observer Jeff Ward was out Thursday, 2/16 and reported the recent about 10 inches of  moist storm snow was being transported and building wind slabs through the day. There was evidence of a few natural wind slab releases and a natural storm slab was noted releasing sometime Thursday. A thin freezing rain crust formed mid-storm cycle and was yet to form a good bond as of Thursday.

More reports Friday near Washington Pass showed moderate snowpack test results at the interface of the storm snow and melt-freeze crust, down about 14 inches. Yet not triggered slides occurred in steep terrain, including steep convexities. Snowmobiles were highmarking in the Washington Pass area Friday with no triggered slides, showing good stabilization in the recent storm snow.  

Central

Thursday afternoon 2/16, warm temperatures had reached the lower east slopes and numerous wet snow avalanches had released, including in Tumwater Canyon.

Reports from the Mission Ridge pro-patrol Friday indicated that the previous wet snowpack had locked up and formed a strong surface crust in most terrain with little to no new snow above.

South

No recent observations. 

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.

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.