Avalanche Forecast
Issued: Feb 15th, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
A mixed bag of conditions seems possible on Tuesday with winter like snow conditions possible in the above treeline and wet snow conditions in the near and below treeline. Several types of avalanche problems will need to be watched for on Tuesday.
Summary
Detailed Forecast
A weak cold front will cause rain or snow to shift from north to south over the Olympics and Cascades tonight to Tuesday morning with a slight drop in snow levels. Up to a few inches of snow should be seen in the above treeline with some more rain in the near and below tree line.
Another weak warm front should lift south to north over the Northwest Tuesday afternoon and night and cause light rain or snow with another slight rise in snow levels.
A mixed bag of conditions seems possible on Tuesday with winter like snow conditions possible in the above treeline and wet snow persisting in the near and below treeline.
This forecast will be conservative and list new wind slab as likely in the above tree line on Tuesday. Watch for new firmer wind transported snow mainly on lee N to SE slopes near ridges. You will need to be able to assess this problem for yourself if you travel above treeline on Tuesday.
You should continue to watch for loose wet avalanche conditions in the near and below treeline on Tuesday. Watch for wet surface snow deeper than a few inches that usually precede loose wet avalanches or other triggered or natural loose wet avalanches. Steep slopes near and below treeline are probably still best avoided on Tuesday.
Glide avalanches won't be listed as a problem but avoid areas below steep rocks still holding snow since these slopes can release at unpredictable times.
Storm slab also won't be listed as a problem but watch for this type of layer in area if you find yourself in an area that rapidly accumulated snow on Monday night. A cooling trend, near freezing temperatures and good bonding should limit the possibility of this type of layer. You can test for it with quick hand shear or shovel tilt tests.
Snowpack Discussion
Weather and Snowpack
Dry weather with the warmest temperatures of the winter occurred last Sunday to Wednesday with temperatures climbing into the 50's and even the 60's.
A pair of warm fronts brought a wide range of new snow amounts in the 2 to 19 inch range with the most at Baker and Paradise about Thursday to Saturday.
Rain and and mild temperatures predominated along the west slopes Sunday and today. NWAC sites in the near and below treeline will have had rain in the 2-6 inch range for the 2 days ending Tuesday morning.
Bonds should be good in the upper snowpack along the west slopes. The mid and lower snowpack should be mostly consolidated and stable.
Recent Observations
Reports from the Mt Baker pro-patrol Saturday and Sunday indicated the 19 inches of storm snow was reluctant to move during avalanche control. A few isolated wind slab pockets were noted along ridges otherwise the warming Sunday afternoon was causing a few loose wet slides on steep slopes.
Reports from Stevens Pass Sunday indicated the 8-10 inches of storm snow became sensitive to ski triggers by Sunday late morning. These slides behaved as loose-wet avalanches as surface snow become increasingly wet.
NWAC pro-observer Dallas Glass was out near Mt Baker today 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.
Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine.
Likelihood
Expected Size
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 16th, 2016 10:00AM
