Avalanche Forecast
Regions: Cascades - North East.
Conservative decision making will be essential Tuesday as recent storm and wind slabs will require additional time to settle and stabilize. Avoid steep open slopes showing signs of recent wind transport. Best to confine travel to lower angled terrain away from wind effects.
Detailed Forecast
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Additional showers are expected Tuesday at continued cool temperatures. Showers should generally be fewer and taper by late Tuesday.Â
Moderate west winds at ridge level should persist Tuesday before diminishing late Tuesday.Â
Recent or new wind and storm slabs will be the main avalanche problems along the east slopes.
New wind slab is mostly likely to be found on NW-SE facing slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab or storm slab instabilities.
New storm slab is likely in areas where new snow rapidly accumulates for more than several hours.
Cloudy cool conditions Tuesday may limit the development of loose wet snow but the sun is gaining power so watch for the development of loose wet snow on solar slopes if extended sun breaks occur.Â
The avalanche danger should gradually decrease Tuesday with less wind and slow settlement and stabilization of new snow and fairly cool temperatures.Â
The persistent slab avalanche problem will not be listed in the northeast zone due to an abundance of other avalanche problems. This problem is most likely to be found on non-solar aspects in the above and near treeline band and stretching into the upper portion of the below treeline band.  This interface is likely getting harder for a human to trigger but if triggered is capable of producing large avalanches. Be aware that at depths approaching the 1 m mark the extended column test becomes a less reliable indicator of propagation across a column. Deeper tests like the propagation saw test or deep tap test may help but layer identification and terrain selection are your best friends for managing a persistent slab danger.
Snowpack Discussion
Weather and Snowpack
During a period of fair weather in late February, widespread surface hoar formed in the northeast zone mainly surviving outside of steeper solar aspects and wind affected terrain. A weak front buried the surface hoar layer in the Washington Pass area about 2/27 and to a lesser extent the central-east zone. Â
Storms have moved across the Northwest almost every day or two the past couple weeks with fluctuating but generally moderate snow levels.
A storm last Wednesday and Thursday caused a warming trend that peaked Wednesday night with very strong west winds seen throughout the Cascade range. About 6-16 inches of snow accumulated through Thursday morning with the higher tallies of over a 1 foot seen at Holden, the NWAC station at Washington Pass and the NRCS site at Lyman Lake and Hart's Pass.
A front on Saturday caused west-southwest winds and light amounts or up to a few inches of snow along the east slopes ending Sunday morning.
A deep surface low-pressure system  moved across the NW Washington Cascades on Sunday. A strong front crossed the Cascades Sunday afternoon. This caused stormy weather in the Cascades with strong shifting southeast to southwest winds and moderate snow along the east slopes. About 8-10 inches of new snow accumulated as of Monday along most east slope areas.
We are no longer tracking any layers of concern formed earlier this winter in the mid or lower snowpack due to lack of recent activity at these interfaces and confirming field observations.Â
Recent Observations
Strong winds on March 3rd caused widespread natural wind slab avalanches in the NE zone. While many were contained to the recent storm snow, one larger slide on a N-NE aspect at Windy Pass likely released down to the 2/27 PWL. The last known human triggered avalanche on this layer was also in the Washington Pass area on March 2nd.Â
Mission Ridge pro-patrol reported a very active day of control on Thursday, March 10th with 1-4 foot slides produced during control work on lee slopes below ridges. Wind slabs were sensitive and ran far. Â Widespread cornice growth was also noted along ridge lines.
The North Cascade Guides report for the Washington Pass area on Friday indicates 20-50 cm of HST on lee slopes. Several pits had a mix of homogeneous snow or crusts in the top meter of snow. Tests gave no results or RP results including on the 2/27 interface. Crowns or debris with sizes to 2.5 was noted from an avalanche cycle on Wednesday to Thursday.
The Guides report for Washington Pass on Saturday noted snow plumes off nearby peaks indicating wind transport and more evidence of the avalanche cycle on Wednesday and Thursday.
The Guides at Washington Pass on Sunday reported large cornices with some releases and large debris. Wind transport was steady through the day but low visibility prevented further observations.
NWAC observer Tom Curtis tested conditions in the Blewett Pass area Monday, 3/14 following the strong storm Sunday. Sensitive storm and wind slabs of up to 20 inches were found in open terrain, especially wind affected slopes. Easy failure in test pits was noted on a crust-facet layer buried beneath the current storm snow, about 16-20 inches. Failures were found with PST and ECT tests on this interface.
Avalanche Problems
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, North West.
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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: Possible
Expected Size: 1 - 1