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Avalanche Forecast

Archived

Feb 19th, 2016–Feb 20th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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The avalanche danger should be greatest early Saturday following the storm Friday. Watch for wind loaded terrain and avoid steep slopes suspected of wind deposits. Conditions should improve as the snow pack slowly stabilizes through Saturday afternoon.

Detailed Forecast

Continued periods of moderate snow at cool temperatures, Friday night, along with strong winds.

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

Heavier precipitation rates Friday night should increase the storm slab possibility by early Saturday. 

Showers should end quickly early Saturday with partial clearing and diminishing winds. Cooler temperatures should continue Saturday. 

Watch for greater depths of storm snow and avoid wind loaded terrain and steep rollover features. 

Storm snow problems should improve through the day Saturday as upper snow layers settle and stabilize.

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.

The warm weather transitioned to rain at high freezing levels over the Mt Baker area that gradually cooled by 2/12, depositing increased 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!   

Snow showers at cooler temperatures arrived Thursday 2/18 followed by a strong front Friday. These storms have deposited storm snow amounts ranging from about 1-2 feet by Friday afternoon.

The new snow has been wind affected at higher exposed elevations, but in general is well bonded to the old wet but draining snowpack. 

The upper snowpack consists of a mix of crusts and wet grains below the recent storm snow with no deeper instabilities of note.

Recent Observations

NWAC pro-observer Lee Lazzara  was out in the Mt Baker backcountry Friday, 2/19 as the front arrived. Strong winds were building wind slab layers on exposed lee slopes near and above treeline. Storm snow was generally well bonded to the old wet and draining upper snowpack. No avalanches were noted and steep slopes were tested in wind protected areas. 

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.