Avalanche Forecast
Issued: Feb 24th, 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
Earlier formed wind slabs should continue to stabilize, but remain aware of these potentially touchy wind slabs on a variety of aspects, most likely those facing westerly. Strong late winter sunshine and mild temperatures should cause possible loose wet avalanches on steeper solar slopes in your area.
Summary
Detailed Forecast
The wind slabs that may have formed Monday night through Tuesday from strong E-SE winds, primarily in the near and above treeline elevation bands, will continue to settle and stabilize, but may still be possible below treeline depending on local loading patterns.
Mild temperatures Wednesday and again Thursday should allow these layers to quickly stabilize, however watch for stiffer previously wind transported snow on a variety of aspects Thursday, especially near ridges.
Temperatures should be even warmer Thursday, so watch for pinwheeling and rollerballing as precursors to more significant loose wet activity and especially be wary of loose wet avalanches around terrain traps, such as slopes that would funnel wet snow like gulleys or depressions, also slopes above cliff bands or dense trees.
Snowpack Discussion
Weather and Snowpack
Dry weather with the warmest temperatures of the winter occurred February 7-10th with temperatures climbing into the 50's in most areas east of the crest. Snow in the northeast zone buried the crust with about 2-3 feet of snowfall starting February 11th through Saturday morning February 20th.
Rain and mild temperatures were seen in the central east and southeast zones last week forming a newer crust further south and outside the Washington Pass zone. An active and cooler pattern buried the crust in the central and southeast zones starting February 17th with about 6-10 inches of snow in the near and above treeline Wednesday through Saturday morning.
Up to a few inches of additional snowfall fell by Monday morning. Dry, cool conditions Tuesday and mild temperatures Wednesday have allowed for continued settlement and stabilization of any recent wind slab layers.
Recent Observations
The pro-patrol at Mission Ridge Saturday reported pockets of ski triggered 6-14 inch wind slab during avalanche control on northeast to southeast slopes above about 5800 feet. These slabs were releasing on the February 17th crust. Later today a skier triggered a 6-10 inch wind slab and was caught and carried but not injured in a northeast facing chute at about 6300 feet.
NWAC pro-observer Jeff Ward was in the Silver Star/Varden Creek area east of Washington Pass Monday and found the Feb 11th crust 80-90 cm down. No avalanche activity has been reported down to this layer in the Washington Pass area. Jeff also found sensitive yet shallow wind slabs near and above treeline Monday.
Tom Curtis was in the Icicle Creek drainage Tuesday and observed light to moderate wind transport near and above treeline. Below treeline, the most recent storm snow was unconsolidated and poorly bonded to the most recent crust.
Large avalanches that are sensitive to skier triggering were recently noted north of the border releasing down to the Feb 11th crust. Although nearby, avalanche activity either natural or skier triggered have not been observed in the Washington Pass zone down to this crust, but this information is still relevant to keep in the back of your mind if traveling around the NE Cascades.
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, West, North West.
Elevations: Alpine, Treeline.
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: Feb 25th, 2016 10:00AM
