Avalanche Forecast
Issued: Apr 19th, 2018 11:10AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
Current avalanche problems are generally associated with a transition from winter to spring. Loose wet avalanches will occur as warm temperatures impact settling snow surfaces. Limit your expose to sun-affected slopes during the middle of the day. Cornices are very large and drooping, so avoid slopes exposed to these large potential avalanche triggers.
Summary
Detailed Forecast
Warm weather with decreasing filtered sunshine Friday will develop Loose Wet avalanches as recent snowfall continues to settle. Limit exposure to sun-affected slopes during the middle of the day. If you see new roller-balls, fresh fan-shaped avalanche debris, or find loose surface snow more than ankle deep, expect loose wet avalanches on steep slopes nearby. Don’t underestimate the power of even small loose wet avalanches. They may carry you into or over slopes where even small avalanches can have large consequences.
Wind Slabs may linger another day on wind-exposed northerly slopes near and above treeline. Watch for textured snow surfaces, wind pillows, and recently-formed cornices and give steeper wind-loaded slopes another day to settle.
Over the winter, cornices have grown very large. Warm air and sunshine encourage these large hanging blocks of snow to droop and ultimately fail. Predicting when and where they will collapse can be extremely difficult. Do not linger areas below large cornices and choose travel routes to limit your exposure to these potential ticking time bombs with the potential to trigger deeper avalanches.
Expect other spring hazards including Creeks opening and flowing high and fast.
Snowpack Discussion
The latter half of this week has brought some reprieve from a wetter-than-normal April with quiescent weather returning to the east slopes of the Cascades and temperatures rebounding above freezing at mid and lower elevations. The warming is impacting a snowpack at various stages of the transition from winter to spring. The warming temperatures are settling the recently accumulated snowfall. Sunshine on Tuesday generated Loose Wet avalanches on south-facing slopes in the highway 2 corridor, where enough recent snow existed to generate the problem.
The active weather pattern ended on Tuesday. An inch of snow accumulated accumulated Monday night into Tuesday morning at cool temperatures. This was accompanied by moderate winds that transported snow in exposed terrain. Wind slabs were reactive on Tuesday near ridges in the Cascade passes and small wind slabs are presumed to have formed in wind-exposed terrain east of the crest. Washington Pass received 11" of accumulated snowfall Sunday night into Monday with cooling temperatures and moderate westerly winds. Around 6-8” (15-20cm) of new snow fell near Washington Pass 4/13-4/14. Air temperatures reached above freezing at Pass level for much of the day Saturday, ultimately generating a rain crust into the near treeline terrain.
We have very limited information about older persistent weak layers on the east slopes of the Cascades. You are most likely to find a reactive persistent weak layer on shaded aspects or at higher elevations above recent rain events. Large cornice failures are the most likely way to trigger such a layer. If you have any information on snowpack conditions consider sharing your observations with NWAC on our public observations page.
Two common persistent weak layers seen in the Northeast Cascades are:
- 3/25 and 3/22: Buried surface hoar layers found on shaded aspects near and above treeline.
- 2/13 Facets above a firm and thick melt-freeze crust can be found in many locations near and above treeline. This layer is thought to be dormant at this time but may re-awaken with a substantial weather input.
Lower elevations further east of the crest have melted back for the season and no longer present an avalanche risk.
Observations
No recent observations.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 20th, 2018 11:10AM
