Avalanche Forecast
Regions: Snoqualmie Pass.
Avalanche danger should increase during the day on Sunday. Watch for areas of newly forming wind slab on lee easterly aspects near and above treeline. Cooling should help limit wet loose avalanche concerns but the potential remains below treeline so watch for shallow wet snow on steeper terrain.
Detailed Forecast
A front band of precipitation and strong winds should stay draped over the US/Canadian border overnight and early Sunday, producing moderate to heavy precipitation over the north part overnight and early Sunday before shifting southward across the remainder of the WA Cascade crest by later Sunday. Â
Snow levels will be gradually lowering from Saturday night through Sunday but mainly gradually.  Moderate to briefly heavy rain or snow should change to showers and gradually decrease late Sunday.  This front should also maintain strong crest level SW winds shifting to NW late.  This should maintain some wet snow conditions below tree line Sunday.  However strong winds and new snowfall should build areas of wind slab on lee northeasterly to southeasterly aspects in these regions near and above treeline.Â
Triggering a wet slab avalanche to a deeper layer is unlikely, but this will continue to be an avalanche concern since recent heavy rain has allowed water to penetrate deep in the snowpack and a step down release to a weak layer/crust from mid-winter cannot be ruled out. To mitigate this concern, generally avoid large avalanche terrain over the weekend and wait for the moist upper snowpack to tighten up. Â
Snowpack Discussion
Recent Weather Summary
Over the past month two major storm cycles moved across the Pacific Northwest. The most recent week long storm cycle occurred in early March and wound down last Sunday. This storm cycle produced similar water equivalents as the February cycle; water equivalents and snowfall totaled about 9-13 inches and 2-6 feet at most NWAC sites near and west of the crest. This cycle was warmer and featured mainly wet snow and rain leading to several natural avalanche cycles during the first week of March. Average freezing levels have been roughly 2000-3000 feet higher thus far in March versus February!Â
The heaviest rain and warming came last weekend and was followed on Monday by a few inches of snow and cooling.  Drier and gradually warmer weather was seen late this week.  A front came through Friday morning with rain and gradual cooling, and deposited several inches of snow above 4000 feet in showers. Some of the heaviest accumulations were from a convergence zone focused on the Stevens Pass and Mtn Loop Hwy area through Friday afternoon.Â
Recent avalanche observations
No avalanche activity was reported Saturday as affects of mild temperatures and sunshine or filtered sunshine were countered by the cooling affects of increasing strong winds. Most reports Saturday indicated surface snow had refrozen to form either crusts of various strengths. Â
The ski patrol at Crystal Mountain on Sunday and Monday produced consistent large wet slab releases with large explosive charges releasing to deep layers from early this winter. These avalanches were generally on N to E slopes at about 6-7000 feet with crowns of 4 to 6 feet and up to 10 feet in spots with the High Campbell chair and some trees destroyed. See photos at the Crystal Mt web site. They also reported similar natural releases were seen in the adjacent Mt Rainier National Park.
On Tuesday 11 March, NWAC observer Dallas Glass also found recent very large wet slab releases on Kendall Peak at Snoqualmie Pass. Several large to very large (very destructive) wet slab avalanches began at about the 5500 ft elevation on primarily W aspects on slopes of about 35-40 degrees and ran about 1000 feet. These slides likely released Sunday night or Monday when the area received over 3 inches of rain to elevations above 5500 feet. A video of the slide area and debris fields can be seen here  NWAC channel.  On Thursday, backcountry skier Andy Hill found wet slab debris from earlier in the week that stepped down to the firm January crust in Great Scott Bowl in the Alpental backcountry with an 8-10 ft crown.  Also, avalanche educator Gary Brill reported about a dozen large slab releases on N thru E aspects up to around 6000 ft following this storm cycle on a flight Wednesday along the west slopes. Â
While it is unlikely these deep wet slab avalanches could be human triggered, it remains a possibility if initiated at a thin spot in the slab. WSDOT professionals and NWAC observers during the middle of the week reported moist snow and a lack of temperature gradient penetrating deep in the snowpack.  Wet slabs will remain a concern especially during times of rain or extended warm periods and are not necessarily tied to the period of heaviest rain or warmest temperatures. With more rain and mild temperatures forecast this weekend, wet slab avalanches will remain a concern near and west of the crest. Here is a link to more information about the wet slabs.
A natural wet loose cycle was reported near Stevens and Snoqualmie during the frontal passage and heavier precipitation Friday morning.  See NWAC observer Jeff Hambelton's video on new wind slab concerns in the Mt. Baker backcountry from Friday. Â
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Photos by Andy Hill 3-11-14, Alpental backcountry off a D3/R3 wet slab from early last week. Â
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
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.
Elevations: Below Treeline.
Likelihood: Possible
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: Possible
Expected Size: 1 - 1
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 2