Avalanche Forecast
Issued: Mar 16th, 2015 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
It's nearly spring and the sun's strength can rapidly create locally dangerous conditions on steeper solar slopes, where even a shallow and slow moving avalanche would be powerful and could force you into unintended terrain traps. Also, watch for weakening cornices along ridges during the warmer part of the day.
Summary
Detailed Forecast
A weak weather system Tuesday should cause cloudy conditions with light rain or snow at times. Only light amounts of new snow are expected and this should not cause a significant increase in danger.
The avalanche danger will be regionally higher along the east slopes in the northeast Cascades.
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The latest installment of warm and dry weather lasted from early to mid-March and led to more snowpack consolidation and a scarcity of avalanche activity. Snowdepths vary greatly across the east slopes... with a regionally healthy snowpack in the northeast Cascades to bare solar and low elevation slopes for the central and southeast Cascades.
Over the weekend, an atmospheric river brought a one-two punch to the Pacific Northwest. Saturday's event brought up to 1.0 inches of water with a snow level around 6500 ft through Saturday afternoon, with much lower totals in the Blewett-Mission Ridge area.
Another inch of water fell more evenly along the east slopes Sunday and Sunday night, with the snow level 6000 feet in the south and 4500-5000 feet in the north. Around 15 inches fell at the NWAC Washington Pass and the Hart's Snotel by Monday morning.
NWAC observer Jeff Ward was in the Hart's Pass area of the northeast Cascades over the weekend and reported touchy yet small loose wet near treeline and growing storm and wind slab concerns by late Saturday afternoon. By Sunday, a few small (size one) ski triggered slides were noted, near the 6000 foot elevation, one dry loose and the other a slab. Storm snow amounts in that region averaged about 16 inches near and above treeline by late Sunday.
Problems
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
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.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 17th, 2015 11:00AM
