Avalanche Forecast
Regions: Stevens Pass.
Dangerous avalanche conditions at Hurricane and from Mt Baker to Snoqualmie on Thursday. Careful snowpack evaluation, cautious routefinding and conservative decisions should be essential.
Detailed Forecast
A warm front will move across the Northwest on Wednesday night followed by the cold front Thursday morning. This will cause southwest winds and further moderate to heavy rain and snow especially from Mt Rainier to Mt Hood. Snow levels should rise to the 4000 foot, 5000 foot and 6000 foot range in the north, central and south Cascades respectively on Wednesday night. Snowfall in the ATL and NTL zones for the 48 hours ending Thursday morning should be in the .5-1 foot range from Mt Baker to Snoqualmie and in the 2-3 foot range from Mt Rainier to Mt Hood. Less snowfall is likely east of the crest.
Southwest winds and moderate to heavy showers should be seen following the front on Thursday morning. Further southwest winds and generally moderate showers should be seen Thursday afternoon. Snow levels should lower a bit to about 4000 feet in the north and 5000 feet in the south following the cold front.
New snow will be very susceptible to strong spring solar effects and strong daytime warming! New or further building storm and wind slab will also be seen. These avalanche concerns will be especially where snowfall is expected to be heaviest from Mt Rainier to Mt Hood.
The avalanche concerns will be listed as very likely from Mt Rainier to Mt Hood, likely at Hurricane and from Mt Baker to Snoqualmie, and possible east of the crest.
Snowpack Discussion
It might be late April but Mother Nature isn't watching the calendar and more weather systems are moving across the Northwest this week.
Recent reports are few and far between. Yesterday the Chinook Pass DOT crew reported large natural and triggered wet loose avalanches on solar aspects. Wednesday morning Mt Hood Meadows ski patrol reported widespread triggered 6-10 inch storm slab avalanches. This afternoon the Mt Hood Meadows ski patrol reports widespread natural and triggered wet loose avalanches in their closed Heather Canyon area.
Avalanche Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1