Avalanche Forecast
Issued: Jan 27th, 2015 10:15AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Persistent Slabs.
NWAC,
Northwest Avalanche Center
There is a high amount of uncertainty to how reactive persistent weak layers in the upper snowpack are to human triggering. Exercise caution on Wednesday and make conservative terrain choices. Loose wet avalanches are still the most likely avalanche problem to encounter, but even that is of low likelihood.
Summary
Detailed Forecast
Cooler temperatures, mostly clouds and a few light showers are expected overnight Tuesday and Wednesday. Only very light amounts of precipitation are expected, if any, and this should not change the overall low danger.
Generally avoid steep slopes, especially near terrain traps where you might be able to push off enough wet snow to start an avalanche large enough to take you for a ride.
Remember, due to the unseasonably low snowpack especially at lower elevations, numerous terrain hazards such as open creeks, partially covered rocks and vegetation are widespread.
Snowpack Discussion
Snow on the back end of the last winter storm one week ago was in the 6-24 inch range east of the crest with the most significant snow recorded at Holden, Washington Pass and due east of Stevens Pass.
The warm and wet system that affected the PNW Thursday through Saturday did push high freezing levels over to the east slopes, but brought drastically lower rainfall totals than the west side; generally less than 1 inch of rain was received for the previous 48 hr ending 4 am Sat along the east slopes.
Recent Observations: Observations by professional guides in the Silver Star and Varden drainages Monday, saw very little evidence of recent avalanche activity as a result of our most recent rain event. There is still evidence of weak snow above the mid January crust, but no pronounced activity from either snowpit tests or ski tests and the recent warming has likely helped strengthen this layer. Where tested, this layer was about 40-60 cm below the surface near treeline about 6600 feet.
NWAC pro-observer Tom Curtis was at Dirty Face, north of Lake Weneatchee on Monday and found the buried crust/facet layer from mid January about 50-55 cm below the surface and also not reactive to tests. While no natural or human triggered avalanches were observed, this is still a layer to keep an eye on.
In a nearby area, NWAC observer Jeff Ward was checking out the terrain on Sugarloaf Mountain, Monday January 26th, seen on this video.
Problems
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
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Jan 28th, 2015 10:15AM
