Avalanche Forecast

A system passing through in Northwest flow Saturday night and Sunday morning should transition to generally light snow showers by mid-day Sunday. A warm front approaching from the west should hold off on producing another round of moderate snow until Sunday evening. Significant W to NW wind transport on Sunday should be confined to the above treeline zone...so continue to expect new wind slab on traditional easterly aspects at higher elevations. 

Generally shallow, new storm slab formed Saturday night and Sunday should be the deepest in the central Cascades...and maybe the most sensitive near and south of Snoqualmie Pass where slight warming Sunday may allow for denser snow to layer on top of lower density snow Saturday night. 

Overall the snow received over the last 2 weeks continues to settle and stabilize. Human triggered large or very large avalanches are becoming unlikely but are still high consequence if able to step down to poorly bonded previous storm or wind layers. Cornices have grown large and are still reported to be sensitive. A cornice failure could provide a large enough natural trigger to trigger a large and destructive avalanche. While the old Jan crust and any remaining weak layers around or just above it are likely 1.5 m to 2 m down in wind sheltered terrain and becoming very unlikely to trigger...it's important to remember where this layer is and where an avalanche could release to under the right circumstances.   

The sun is starting to get stronger as we head toward March. Watch for any sun effects Sunday morning over the south Cascades to quickly produce roller balls and pinwheels on solar slopes that could trigger a loose wet avalanche or a wind or storm slab layer on a steep slope.

There's plenty of new snow to go around...continue your careful snow pack evaluation and cautious terrain selections on Sunday.

Recent Northwest Weather

An extended mild and dry period occurred the latter half of January generally causing a crust to form in all areas. Very cold weather followed in early February which generally produced low density snowfall and faceting near and just above the crust.

Saturday was the first relative break in a seemingly endless storm cycle over the last two weeks. Constant frontal systems produced periods of strong winds and heavy snowfall. The water equivalent over the past 12 days is about 9-15 inches with snowfall about 7-12 feet at NWAC weather stations near and west of the crest.

Observations for Washington Cascades near and west of the crest

Several avalanche cycles have been seen in the last 2 weeks.  The forecast attention near and west of the crest will be focused on recent storm and wind layers. Note that persistent slab is a concern east of the Cascade crest. Be sure to read the forecast for that area if you venture even slightly east of the crest.

The late January crust layer and associated weak layers are now deeply buried but continue to produce big results with big explosives by area ski patrol on wind loaded slopes near and above treeline. Perhaps of less relevancy to a backcountry forecast but still plenty interesting is the average 6' crown with a maximum of over 15' Alpental ski patrol was able to produce with large explosives Friday in their back bowls. Of greater concern to backcountry skiers and riders should be a natural wind slab avalanche that occurred near White Pass on a easterly aspect near treeline Friday morning. This natural avalanche produced an 8' crown and underscored NWAC observer Tom Curtis's report from the area Friday of heavy wind loading on lee slopes near 7000 feet. 

Pictures of wind slab avalanche and large cornice growth near Gunsight Peak, White Pass, Photo by Chris Talbot, Pro Patrol 2-21-14 

Here is a video observation from NWAC observer Dallas Glass in the Snoqualmie Pass area Wednesday identifying midweek storm snow instabilities. Dallas re-visited the Snoqualmie Pass area Friday and reported a settling and stabilizing snow pack. He saw possible 30-50 cm wind slab layers on lee slopes and storm slab that was becoming less reactive except on isolated terrain features.

The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.

Keep an eye on your riding partner in the deep snow until the new snow settles and the risk of SIS subsides.