Avalanche Forecast
Issued: Feb 22nd, 2016 10:16AM
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
Watch for new or previous firmer wind transported snow on a variety of aspects near and above treeline and loose wet avalanches on steeper solar slopes Tuesday.
Summary
Detailed Forecast
Colder air trapped along the east slopes and easterly flow near the Cascade crest should translate to a slow warming trend on Tuesday despite mostly sunny skies near and above treeline.
E-SE winds should be light, except moderate near the Cascade crest for the central and southeast Cascades. This will locally help redistribute recent snowfall to non-traditional westerly aspects forming generally shallow but potentially touchy windslab. New wind loading should primarily occur in the near and above treeline elevation bands, but may still be possible below treeline depending on local loading patterns.
Watch for new or previous firmer wind transported snow on a variety of aspects Tuesday: Don't let the combination of Moderate avalanche danger with non-traditional lee aspects/cross-loaded slopes catch you by surprise!
A secondary avalanche concern on Tuesday will be loose wet avalanches on solar slopes. Despite cool freezing levels, late February sunshine should activate steeper solar slopes as the day progresses. Watch for pinwheeling and rollerballs as precursors to more significant loose wet activity and especially be wary of loose wet avalanches around terrain traps.
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.
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 storm in the near and above treeline Wednesday through Saturday morning.
A weak front on Sunday only brought up to a few inches of additional snowfall through Monday morning.
Recent Observations
The North Cascades Mountain Guides sent a report Friday for the Washington Pass area and report that the February 11th crust is found at about 65-80 cm down. Some but not all tests give hard sudden collapses with sudden propagation. Also some stiff pencil hard wind slab gave easy shears near or below ridgelines with some sensitive wind slab avalanches observed on NE aspects during the middle of last week.
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 slab 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.
Large avalanches that are sensitive to skier triggering continue to be 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 is still relevant information 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: All aspects.
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: South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 23rd, 2016 10:16AM
