Avalanche Forecast

A moderate cold front will approach from the west Thursday night and cross the Northwest on Friday morning. This will be accompanied by increasing winds, moderate rain or snow and slightly lowering snow levels. Showers following the front should decrease Friday afternoon. A convergence zone may enhance showers near Stevens Pass Friday afternoon.

New wind slab is likely on lee slopes. You should be most likely to trigger a wind slab on north to southeast aspects near and above treeline. Watch for signs of firmer wind transported snow or cracking snow.

New storm slab is also likely on sheltered slopes again mainly near and above treeline. This is most likely in any areas that receive an inch of snow or more an hour for at least a few hours.

It is now March and the sun is getting stronger. Watch for sun effects on new snow mainly on solar aspects but possibly aspects as well. Wet loose avalanches are becoming more likely if you see pinwheels or initial small natural wet loose releases.

In sheltered areas where the winds are not strong and the snowfall not heavy the increase in avalanche danger should be more limited. In such areas the cooling trend may also help create right side up layering with lower density snow near the surface.

Triggering a wet slab avalanche to a deeper layer is unlikely, but this will be a continued concern since recent heavy rain has allowed water to penetrate to these deeper potential weak layers from mid-winter.

Over the past month two major storm cycles moved across the Pacific Northwest.

The first two week storm cycle ended 25 February and deposited about 7-12 feet of mostly wet heavy snow at most NWAC sites near and west of the crest and caused avalanches across the region.

The second week long storm cycle wound down last Sunday and produced similar water equivalents as the February cycle.  Water equivalents and snowfall for the the second cycle were about 9-13 inches and 2-6 feet at most NWAC sites near and west of the crest. So this was a cycle of wet snow and rain. This produced avalanches including reports from Holden Village, Stevens Pass, Tumwater Canyon, MIssion Ridge, Alpental and Snoqualmie with pass closures at times.

Looking down and at the start zone of a snow cat triggered large avalanche at White Pass on Sunday morning 9 March. Photo by Chris Talbot/White Pass Ski Area.

The ski patrol at Crystal Mountain on Sunday and Monday produced consistent large wet slab releases with large explosive charges releasing to deep layers from early this winter. These avalanches were generally on N to E slopes at about 6-7000 feet with crowns of 4 to 6 feet and up to 10 feet in spots with the High Campbell chair and some trees destroyed.  See photos at the Crystal Mountain web site. They also reported similar natural releases were seen in the adjacent Mt Rainier National Park.

On Tuesday 11 March, NWAC observer Dallas Glass also found recent very large wet slab releases on Kendall Peak at Snoqualmie Pass. Several wet slab avalanches began at about the 5500 ft elevation on primarily W aspects on slopes of about 35-40 degrees.  They were classified as D 2.5, R 2/3 natural wet slabs and ran about 1000 feet.  These slides likely released Saturday when the area received over 3 inches of rain to elevations above 5500 feet. A video of the slide area and debris fields can be seen here  NWAC channel.

While it is unlikely these deep wet slab avalanches could be human triggered, it remains a possibility if initiated at a thin spot in the slab.  As liquid water has now penetrated to deep in the snowpack in places that have received significant recent rain this concern may remain into the spring, especially during times of rain or extended warm periods. As a result of this recent activity wet slab avalanches are listed as a concern near and west of the crest. Here is a link to more information about wet slabs.

Cycles of daytime warming and night time cooling have generally been seen the past couple days. The upper snowpack has temporarily stabilized and no significant avalanches have been reported the past couple days. Rain crusts at or near the surface in many areas were generally firm and fairly thick Thursday morning and are only softening on Thursday afternoon.