Avalanche Forecast

Friday night should be mild with increasing mid and high clouds, likely preventing a solid refreeze tonight in many areas and elevations. A relatively weak frontal system will lift over the area from south to north beginning late Saturday morning through Saturday afternoon and will be followed by post-frontal showers. Rain should generally be seen below 5500 feet. There should be just enough new snow in the alpine to build areas of new but generally shallow wind slab on lee aspects above treeline. Look for an abrupt wind shift mid-day. Older wind slab formed earlier in the week above treeline should be unlikely to trigger on Saturday. 

Potential afternoon sunbreaks are most likely in the southern part of the Cascades, and would help activate loose wet avalanches on solar aspects with fresh snow mainly near and above treeline. Loose wet avalanches at lower elevations should 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. 

Cornices are still large so give them a wide safety margin. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

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

The active weather pattern continues into late April for the Pacific Northwest despite what the calendar says. Between Monday and Thursday night, Mt. Baker picked up about 3 inches of water equivalent (WE) while other areas along the west slopes picked up 1 - 1.5 inches of WE. Much or all of this fell as snow above 5000 feet in the north and 5500-6000 feet in the central and south Washington Cascades. Natural loose wet avalanches likely occurred throughout this period as the snow-line oscillated or on solar aspects at lower elevations during sunbreaks. 

Friday was a warm day with most NWAC stations in the Olympics and Cascades reaching into the 40s and 50s. Breezy E-SE winds were seen in the Passes and in the southwest Cascades including Mt. Rainier and Crystal. 

Recent observations

The Chinook Pass DOT on Thursday reported loose wet avalanches becoming increasingly senstive during sunbreaks below 5000' with ski cuts and explosives, with larger slides gouging down to older wet snow. One 30-40 cm wind slab was triggered below ridgecrest with explosives.

NWAC pro-observer Lee Lazzara was in the Mt. Baker backcountry on Wednesday. Lee found recent wind slab on lee slopes near and just above 5000' up to 30 cm thick but unreactive in ski or snowpack tests. Lee observed a large recent glide avalanche on Mt. Herman (see Lee's Instagram post) as well as evidence of a recent loose wet cycle from earlier in the week.

Lee was back out on Friday in the Baker backcountry on Ptarmigan Ridge. Lee observed numerous loose wet slides on all aspects near and below treeline. Natural cornice fall along Ptarmigan Ridge ripped out a D2.5 wind slab on a north aspect (see photo below, thanks Lee!), and other natural cornice fall was noted as well. Note the massive cornices in the photo! 

Photo by Lee Lazzara, 4-21-17