Avalanche Forecast
Regions: Olympics.
Loose slides or soft storm slab will become more likely with subtle daytime warming in the afternoon or during intense precipitation rates. Watch for wind slab on lee aspects at higher elevations. Cautious terrain and travel decisions are necessary for a safe Sunday; Considerable means skier triggered avalanches are likely!
Detailed Forecast
New snowfall received Saturday night and Sunday may bond poorly to thin melt-freeze/sun crusts found at lower elevations and solar aspects. Heavier showers Sunday will promote storm instabilities within the new snow.  More snowfall is expected near and south of Mt. Rainier Sunday during the daylight hours. A Puget Sound Convergence Zone may produce locally heavy snowfall Sunday evening between Stevens and Snoqualmie Passes. Pay attention to quickly changing surface snow characteristics; April avalanches involving new snow often catch those expecting a more predictable spring regime. Last year, we had 2 avalanche fatalities in mid-April.Â
New snowfall will still be susceptible to strong spring solar effects and daytime warming Sunday despite the cool snow levels and mostly cloudy skies forecast. Watch for wet surface snow deeper than a few inches, natural or triggered snowballing, and small natural wet loose avalanches which usually precede larger avalanches on solar slopes.
New wind slab should build on Sunday on lee slopes mainly above treeline. Watch for signs of firmer wind transported snow or cracking snow.Â
Despite the cool temperatures recent loading and daytime warming will continue to stress cornices.  Give them a wide berth and avoid travel below them...especially in the afternoon.Â
Snowpack Discussion
The last full week of April has felt more like winter than spring; the Forks, WA freezing level has averaged 4300 feet over the last week which is almost a 1000 feet lower than the average for the entire month of March. Upper NWAC stations at Green Valley, Crystal Mt, Paradise, MRNP, top of Alpental (measured by ski area), Snoq Pass, Pigtail Peak, White Pass, and Timberline, Mt. Hood all experienced a second snowdepth maximum with snowdepths equaling snowdepths from late March or the first week of April. While your favorite ski area or trailhead parking lot might be looking a bit sad this time of year...keep in mind there's still plenty of snow the higher you go.
Water equivalents at NWAC stations near and west of the crest for the 4 days ending Friday morning are 1.5-3.5 inch range with the most at Paradise and Mt. Baker. Snowfall received during the span in the near treeline zone is in the 1-2 foot range with the most at Paradise and the top of Alpental, and with more snow at higher elevations.  East of the crest stations received about 0.5-1 inch of water during this 4 day stretch.Â
Generally cold temperatures, light winds and light snow showers with sunbreaks were seen on Friday and Saturday...allowing for gradual settlement of this week's snow but also potentially preserving any recent wind or storm slab instabilities in the near and above treeline zone especially on non-solar aspects.  Breakable melt-freeze crusts have been reported at lower elevations and on slopes receiving sunbreaks. Â
Avalanche observations (note that we receive far less observations than during winter):
Mt. Baker:  On Friday near Church Mtn, Brian Kennedy reported small wet loose slides on solar aspects becoming more reactive in the afternoon with sunbreaks and warming with a few point releases stepping down and entraining soft slabs about 20" (50 cm) down, but not propagating.Â
Alpental: The Alpental ski patrol reported a widespread natural avalanche cycle Wednesday night followed by easy ski triggering in the above and near treeline zone Thursday producing 8-12" storm slabs. Large wet loose avalanches were easily ski triggered below treeline Thursday.  With explosives Friday, Alpental patrol produced loose slides that entrained and ran further than the Wed night natural cycle. Ski cuts Friday produced isolated soft slabs.Â
Chinook Pass: On Thursday morning the DOT crew reported a large wet loose avalanche that reached the road entraining 12-16" of new storm snow and sliding on top of a thin crust formed Wed PM (see photo by John Stimberis, DOT). After an extended period of sunshine Thursday, a very large wet loose involved moist or wet snow from below the thin crust and also reached the road. Ski cutting produced easy results.   Â
Tatoosh Range, MRNP: On Saturday, NWAC Observer Dallas Glass found shallow but hard wind slab that was easily ski triggered on a N aspect above treeline (see below). Dallas also found widespread evidence of point releases from earlier in the week that had stepped down to lingering slab instabilities. Highlighting the power of late April insolation during this cool week, check out this picture from Dallas of a glide avalanche on a SW aspect at 5000'; the new snow from this week released on a lubricated smooth rock surface.Â
Eastside: At lower elevations and further east of the crest there has been less recent precipitation and a few recent reports on Turns-All-Year that describe more stable and spring like corn snow in the afternoons.
D1-R1-HS-ASi-N, Tatoosh Range, Dallas Glass 4-26-14
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: 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.
Likelihood: Possible
Expected Size: 1 - 1