Avalanche Forecast

A refreezing of surface snow on solar aspects is likely in most areas on Wednesday night.

Then partly or mostly sunny weather but with slightly cooler temperatures is expected on Thursday.

But spring sun angles and power are increasing and should re-melt surface snow again to some extent on solar slopes again on Thursday.

This should make further human triggered wet loose avalanches possible mainly on direct solar slopes by the afternoon. Watch for pinwheels and surface wet snow deeper than a few inches.

Areas of old wind slab may still be possible on lee slopes above treeline at higher elevations. Watch for signs of older firmer wind transported snow.

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 February 25th 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, Alpental and Snoqualmie with pass closures at times.

Wet loose avalanche on 5 March on Spiral Butte at White Pass. Photo John Stimberis/WSDOT.

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 deep 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, especially if initiated by a thin spot in the slab such as near rocks or trees.  As liquid water has now penetrated to deep in the snowpack in places that have received significant recent rain these concerns should remain into the spring, especially during times of rain or extended warm periods.  It may also be possible to initiate a wet slab release via a loose wet avalanche triggering a deeper layer.  As a result of this recent activity, wet slab avalanches will now be listed as a concern near and west of the crest. Here is a link to more information about wet slabs.

NWAC observer Jeff Hambelton reported frozen surface snow then deep boot penetration and likely wet loose avalanche conditions in the north Cascades on Tuesday afternoon.

The Crystal Mountain ski patrol reports pinwheels and surface point releases on solar slopes on Wednesday.