Avalanche Forecast

The weather is finally shifting this week from the winter-like pattern so far this spring to a sunny, warmer weather pattern. Mostly sunny weather should be seen on Thursday with light winds, warmer temperatures and freezing levels rising to about the 8000 foot range.

Due to the heavy snow the past couple days, warmer temperatures, and strong spring sun that will melt the recent snow, we expect more widespread loose wet avalanches on Thursday.

Loose wet avalanches will be most likely on steep solar slopes but are likely on other slopes as well. In general the heaviest storm snow has been on the volcanoes especially Mt Hood. Large or very large avalanches loose wet avalanches are likely where there has been heavy storm snow - say more than about 6 inches. Strong spring sun can rapidly melt and destabilize new snow. Underlying frozen previously sun affected firm snow can provide good smooth bed surfaces - this includes ski runs at closed ski areas. Very dangerous avalanche conditions are expected and backcountry travel in avalanche terrain where there has been heavy recent storm snow is not recommended on Thursday.

Careful snowpack evaluation and cautious routefinding will be essential and shallower storm snow will also likely be touchy to triggering in other areas.

Other types of avalanches will be possible on Thursday.

Nearby glide cracks and extensive loose wet avalanches can indicate that wet slab avalanches are possible. Both loose wet and wet slab avalanches are powerful and dangerous.

Wind slab may may still be possible on previous lee slopes at higher elevations.

Cornices should be starting to melt back but may remain unstable during prolonged warmer weather. Avoid potential cornices which can break well back from the edge along ridges and avoid traveling in areas underneath cornices on ridges above. See our blog post about cornices here.

Due to stronger winds and heavier snow, conditions are likely to be more dangerous above the crest level on the volcanoes.

Don't linger or move one a time if you decide to travel under rock slabs holding snow where sudden glide avalanches can release.

Sunny and warmer weather is expected the next few days. It is currently difficult to say how long backcountry snow conditions will be unusual and will merit extra attention. Hopefully some backcountry reports will help to make this more clear the next few days.

Say goodbye to winter...but hello to a spring avalanche cycle.

Weather

A strong front, and then an upper low pressure system and cold unstable air mass crossed the Northwest on Monday night and Tuesday. The strongest winds and thunderstorms, and heaviest snow were generally in the south Cascades especially Mt Hood.

Storm snowfall for the 2 days ending Wednesday morning is about 4-6 inches at Hurricane, 6-23 inches along the west slopes of the Washington Cascades with the most on the volcanoes and generally above the pass levels, about 20-31 inches at Mt Hood, and perhaps about 4-8 inches along the Cascade east slopes at higher elevations. This is a lot of snow for this time of year especially at Mt Hood, and the sun will melt and destabilize this snow the next few days.

Observations

Communications to the base weather station are out at Mt Baker likely due to lightning on May 4th. But the ski area crew there reported about 15 inches of storm snow there on Tuesday.

Via the NWAC Observations page, backcountry skiers at Washington Pass on Tuesday reported 5-8 inches of storm snow that was not well bonded to the previous frozen sun affected snow. On south slopes they triggered several storm slab avalanches that gave debris piles 4 ft deep x 150 ft wide.

The WSDOT crew at Chinook Pass on Wednesday reported that skis and explosives triggered 6-12 in loose wet and storm slab avalanches on specific solar slopes that were large relative to the paths. Larger, widespread loose wet avalanches due to more sun and warmer weather are expected there on Thursday.

NWAC observer Laura Green took a trip up to 5800 ft on Mt Hood on Tuesday. Stormy weather with strong winds, graupel and thunder made for an exciting tour. She found about 12 in of storm snow without signs of instability on lower angle NE to SE slopes in trees on her below treeline tour.