Avalanche Forecast
Regions: Stevens Pass.
A mix of winter and spring conditions is starting to be seen in the Cascades. You will need to watch for a variety of concerns on Monday.
Detailed Forecast
A weak vertically aligned low pressure system should drop south over the northeast Pacific Ocean and Northwest coastal waters Sunday night and Monday. This should cause decreasing winds with mostly sunny weather over the north Cascades and partly sunny weather in the south Cascades on Monday.
The mix of winter and spring snow conditions should continue on Monday. The main concern should begin to shift to wet loose avalanches on Monday. This should be likely on solar slopes in all 3 elevations bands on Monday and will be possible on non-solar slopes. Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches. Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences.
Watch for areas of recent wind slab on lee slopes. This is likely on shaded north to east slopes near and above treeline. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.
East winds will be seen in the lower Cascade passes mainly Stevens and Snoqualmie on Monday. But warm afternoon temperatures and solar effects should consolidate or melt surface snow in the lower Cascade passes on Sunday and Monday and limit or mostly eliminate snow available for transport. So new small areas of wind slab will not be listed as a concern at Stevens and Snoqualmie on Monday. But remember to also make you own evaluations for this concern if you are in these areas on Monday.
Recent storm slab may need another day to stabilize on Monday. This is possible on sheltered slopes where there was recent heavy snowfall or graupel which may have formed temporary weaker storm layers. This shorter lived concern should be above treeline due to cooler temperatures there.
Remember to watch for cornices if you venture onto ridges on Monday and avoid slopes below cornices. Cornice failures are normally seen during the transition to spring weather.
Snowpack Discussion
The weather pattern got active again over the Northwest starting last Tuesday. There has been about 1-3.5 feet of snowfall in the 5 days ending today at higher elevation NWAC stations near and west of the crest. Less snow has been seen at lower elevations.
Avalanche conditions also got active this week. We are now seeing winter snow conditions mainly on shaded slopes at higher elevations and spring snow conditions on solar slopes and at lower elevations. Here are a some reports for the past few days.
NWAC observer Jeff Hambelton was near Church Mt along the Mt Baker highway on Wednesday. He saw several small but natural and human triggered storm slab avalanches on lee aspects near treeline likely failing within the new storm snow. He was at Table Mt near the Mt Baker ski area on Thursday and saw widespread natural wet loose avalanches on all aspects with solar effects and daytime warming.
Storm slab on Church Mtn 26 March by NWAC observer Jeff Hambelton.
A front crossed the Northwest on Friday. The Mt Baker ski patrol reported large ski triggered wet loose avalanches on Friday. The Alpental ski patrol and Snoqualmie DOT reported a natural cycle of loose snow avalanches on late Friday which were drier in the upper elevations and wetter at the lower elevations. NWAC observer Tom Curtis was at White Pass on Friday and reported 4-8 inch wind slab conditions at about 5800 feet.
Wind slab conditions near White Pass on 28 March by NWAC observer Tom Curtis.
Reports from over the weekend include the following. Ski cuts Saturday at the Mt Baker ski area gave mainly isolated wet loose avalanches below 4000 feet. NWAC observer Jeff Hambelton on the west side of Mt Baker Saturday reported building wind slab above about 6000 feet. The Alpental ski patrol reported a natural cycle of loose snow avalanches on Saturday night. Today the Mt Baker and Alpental ski patrols reported isolated 4-8 inch storm slab avalanches releasing in storm layers.
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: South East, South, South West.
Elevations: All elevations.
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
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.
Likelihood: Possible
Expected Size: 1 - 1