Avalanche Forecast

On Thursday, freezing levels should remain near or above 10,000 feet with recent strong NE crest level winds becoming very light. The very warm daytime temperatures and the late March sun will focus the avalanche danger on wet snow concerns. High freezing levels, light winds and sunny skies over the next several days will cause natural loose wet avalanches on solar aspects and increase the odds for low likelihood/high consequence problems, especially cornice failures and glide avalanches.

Melt-freeze crusts can quickly break down with intense spring sunshine. In areas that have received more recent snowfall, small loose wet avalanches have the potential to entrain deeper layers. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences. Plan to avoid steep solar slopes by late morning/mid-day to minimize the problem.    

The likelihood of triggering older wind slabs continues to diminish, however, in isolated areas above treeline, a mix of older wind slab on lee easterly aspects and newer wind slab on the south through westerly aspects will maintain wind slab potential on a variety of aspects. Watch for cracking and firmer or chalky wind transported snow. 

Many areas have massive cornices along ridge-lines, watch for those overhead hazards. Unlike the loose wet problem, you may not have much notice that a cornice is about to fail. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.

Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces (see Lee's filmstrip photo for a recent example). 

Weather and Snowpack

Snow accumulations Wednesday 3/23 to Friday 3/25 varied based on elevation with only a few inches below 4000 feet and 6-21 inches above. This snow was generally well-bonded to a moist crust buried March 21st/22nd. 

A strong front,  followed by a large upper trough and a cool unstable air mass crossed the Northwest Sunday. Along the west slopes, most locations saw a few inches of accumulation with the highest totals of roughly 10" at Snoqualmie Pass and Paradise. Thanks to a convergence zone aimed at Snoqualmie Pass Sunday evening, the top of Alpental accumulated 17". 

Crest level winds were moderate out of the NE on Tuesday through early Wednesday before diminishing Wednesday afternoon.  Most NWAC stations ranged from the mid 40's to upper 50's by Wednesday afternoon, with Snoqualmie Pass into the 60's! 

The frequent March storms have built unusually large cornices along many ridges as noted by field observers over the past several days.

The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

On Saturday large avalanches were observed on the upper elevations of the south side of Mt. Rainier, likely due to serac fall. Travelers to Camp Muir reported the avalanches on TAY and the NWAC observation page.

Alpental pro-patrol reported some pockets of soft wind slab up 17" during morning control work Monday morning. Along the lower mountain, the loose wet potential increased as the sun popped out mid-day.

Lee Lazarra was in the Table Mountain/Mt. Herman backcountry of Mt. Baker Monday. He found Sunday's storm snow generally right side up and well bonded to older snow or a sun crust 25-30 cm down. Wind slab was sensitive in isolated areas near treeline, with new wind slab forming on south through west aspects. Lee also observed debris from a glide avalanche on Mt. Herman that released either Friday or Saturday, highlighting this sporadic, yet ongoing problem in the Baker area. 

Via the NWAC observation page, a skier triggered and was carried in a small slab avalanche above Source Lake on the Chair Peak side Monday evening.