Avalanche Forecast

Issued: May 3rd, 2017 11:00AM

The alpine rating is below threshold, the treeline rating is below threshold, and the below treeline rating is below threshold.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

The highest freezing levels/warmest temperatures of the spring are forecast Wednesday and Thursday. The potential for wet snow avalanches and cornice failure will rise substantially over this period creating dangerous avalanche conditions. Travel in avalanche terrain is not recommended during this time.  

Summary

Detailed Forecast

Weather: 

Rain associated with a warm front should come to an end from south to north on Wednesday and be followed by a general clearing trend for Mt. Hood, the Olympics and the central and south Washington Cascades. Sunshine and isolated mountain showers are expected for these areas Wednesday afternoon. However, cloud cover, shower activity, and moderate alpine winds will linger through most of Wednesday in the north Cascades.

Wednesday night should be mostly clear. 

On Thursday, after a sunny start, showers and thunderstorms will develop in the afternoon and generally move from south to north. Some thunderstorms may locally become strong. Showers and thunderstorms will continue Thursday night.  

Freezing levels will range from 11,000 to 12,000+ feet from Wednesday through Friday morning, with the warmest mid-mountain (5000 feet) temperatures expected Thursday afternoon. These will be the highest freezing levels seen since mid-February. 

Avalanche hazards: 

The threat of wet snow avalanches and cornice failure will rise substantially Wednesday and Thursday due to the warm weather and create dangerous avalanche conditions! Travel in avalanche terrain is not recommended during this time.  

The likelihood of loose wet avalanches will increase on steeper slopes on all aspects and elevations. Periods of rainfall at higher elevations will increase the loose wet potential where recent snowfall at higher elevations is available for entrainment. Periods of strong spring sunshine paired with warm temperatures will quickly break down local melt-freeze surface crusts formed overnight and activate loose wet snow.

Watch for surface wet snow deeper than a few inches, pinwheels and initial small loose wet avalanches that indicate an increasing loose wet avalanche danger. Loose wet avalanches at lower elevations may be less likely to initiate naturally, but if skier triggered, could entrain older snow layers and become large in specific areas. Keep this in mind around terrain traps and do not underestimate the power of even small loose wet avalanches. 

Cornices will weaken during this stretch! Many cornices are still large, and the best advice during this period is to avoid traveling near or below them all together. Realize that natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Cornice failures above treeline may trigger lingering wind slab on lee slopes in the alpine. See a blog post regarding cornices here.

Avoid unsupported slopes with overhanging blocks of snow and smooth rock underneath. Glide avalanches are difficult to predict and can release at any time, not just during the heat of the day.

Snowpack Discussion

Due to the unusually cool and wet spring, our snowpack near and above treeline is in transition from winter to spring conditions in both the Olympics and Cascades. Normal spring-time consolidation has not happened at higher elevations due to this active and cool pattern.

Average March Freezing Levels Forks, WA  Salem, OR Spokane, WA 4295 feet 5795 feet 5152 feet

 

Average April Freezing Levels Forks, WA Salem, OR Spokane, WA 4733 feet 5497 feet 6222 feet

Valid until: May 4th, 2017 11:00AM