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Avalanche Forecast

Archived

Feb 18th, 2016–Feb 19th, 2016

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

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The avalanche danger should increase Friday afternoon and evening due to building wind and storm slab. Cooler temperatures should limit the loose wet problem to below treeline but wet snow hazards will continue. Change your travel plans accordingly if local conditions differ from forecasted weather and/or snowpack conditions.

Detailed Forecast

Continued periods of light to moderate snow at cool temperatures, both Thursday night and renewing during the day Friday are expected, along with strong winds.

This weather should build wind slabs on lee slopes near and above treeline, especially by Friday afternoon. Watch for firmer wind transported snow, mainly on the lee slopes facing N to SE, below ridges. 

 Heavier precipitation rates Thursday afternoon and evening, and again Friday should increase the storm slab likelihood.  

Despite the cooling trend, loose wet avalanches will remain possible below treeline Friday especially on steeper southerly facing slopes. Watch for wet surface snow deeper than a few inches that usually precede loose wet avalanches or other triggered or natural loose wet avalanches. 

Glide avalanches also won't be listed as a problem, but avoid areas under steep rocks still holding snow since these slopes can release at unpredictable times. Look for glide cracks in steep terrain to offer clues of the slab undergoing downhill creep. 

Snowpack Discussion

Weather and Snowpack

Dry weather with the warmest temperatures of the winter occurred February 7-10th with mild temperatures and high freezing levels, leaving behind, well settled older snow and a strong melt-freeze crust.

Storms late last week deposited a wide range of storm snow amounts ranging from a few inches to 18 at Mt Baker. 

Rain and mild temperatures dominated along the west slopes Sunday and Monday. NWAC sites in the near and below treeline recorded 2-6+ inches of mostly rain over the 2 days ending early Tuesday morning. The Paradise station recorded over 5 inches of precipitation (mostly rain) in the 24 hours ending Monday 4am!

Mild temperatures with spotty light rain were seen on Tuesday and Wednesday.  

Cooler air and showers Thursday 2/18 have deposited 4-8 inches of new storm snow by Thursday afternoon.

The upper snowpack consists of a mix of crusts and wet grains with no deeper instabilities of note and new increasing storm snow amounts well bonded to old surface.  

Recent Observations

NWAC pro-observer Dallas Glass was out near Mt Baker Monday and reported several recent large loose wet avalanches on steep north slopes near and below treeline. He also reported a large glide avalanche on a similar slope. Dallas was out again in the same area Tuesday and reported a widespread cycle of loose wet and wet slab avalanches occurred Monday night during heavy rain and snow on most aspects in the 4300-5000 foot range. A 1-2 inch surface crust by this morning had improved surface snow stability.

NWAC pro-observer Tom Curtis was near Stevens Pass Tuesday and reported many recent loose wet avalanches mainly on north to east slopes at about 5000 feet. A pit had water pooling above a crust at 35 cm with weak wet snow below the crust and a PST test indicating propagation below the crust. He also noted glide cracks on nearby slopes.

Mt. Baker and Alpental pro-patrols continue to report glide cracks and glide avalanches on steep rock faces in their areas due the continued mild temperatures and frequent rainfall.  

NPS ranger above Paradise Thursday morning, 2/18, reported new storm snow of 4-6" bonding well to moist crust with no avalanches of note, other than localized small dry-loose on steep slopes.

NWAC observer, Ian, in the Alpental Thursday 2/18 indicated similarly to Paradise: shallow new snow over moist thin crust, well bonded and no avalanches or indicative tests noted. 

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.