Avalanche Forecast

Issued: Feb 14th, 2015 10:00AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Loose Wet and Persistent Slabs.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Watch for possible loose wet snow avalanches mainly on solar slopes on Sunday east of the crest.

Summary

Detailed Forecast

An amplifying upper ridge over the US and BC coastal waters will dominate the weather the next few days. This will cause sunny, warmer weather in the Olympics and Cascades Sunday and early next week.

The main problem to watch for east of the crest should be possible loose wet avalanches. Watch for initial rollerballs or surface wet snow deeper than few inches. While this is expected mainly on solar slopes midday watch for it on other aspects as well. Overnight cooling and surface refreezing will limit this problem on non-solar slopes and during the night and morning hours.

As a result of the overall low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.

Snowpack Discussion

Warm and wet southwest flow directed a series of fronts across the Northwest from about February 5th-10th. The east slopes had a variety of weather and snow conditions. The Harts Pass Snotel and the NWAC Washington Pass weather station's total snow gages indicated about a foot of snow. Other areas east of the crest had less snow or rain. Mild temperatures have been seen the past few days and today.

NWAC pro-observer Jeff Ward is at Hart's Pass and reports only some small loose wet avalanches the past couple days.

The North Cascade Guides reported a small wind slab remotely triggered from a shallow area near rocks with facets last Monday. So there is still variability east of the crest within the last week.

Regarding the potential January 15th persistent slab in the northeast Cascades zone; NWAC pro-observers and the North Cascade Guides the past couple weeks found the January 15th facet/crust layers at anywhere from 35 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. So the January 15th facet/crust layers are stabilizing and becoming very unlikely for a human to trigger. A very large natural avalanche that may have run on this layer east of Washington Pass was likely tied to the heavier precipitation and warming during the February 5th-10th period.

Problems

Loose Wet

An icon showing 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.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1

Persistent Slabs

An icon showing 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.

Aspects: North, North East, East, West, North West.

Elevations: All elevations.

Likelihood

Unlikely

Expected Size

1 - 1

Valid until: Feb 15th, 2015 10:00AM