Avalanche Forecast
Regions: Cascades - North East.
The snowpack may remain reactive and dangerous on Saturday and is only beginning the spring stabilizing process. Backcountry travel in avalanche terrain above treeline is not recommended on Saturday. Careful snowpack evaluation and cautious routefinding will be required in other areas.
Detailed Forecast
Another front will cross the Northwest on Saturday. This will bring another day of increasing strong alpine winds and increasing rain or snow to the Olympics and Cascades. Snow levels should rise up to about 4000 feet in the northeast Cascades and perhaps about 5500 feet in the southeast Cascades.
Wind slab should be suspected mainly above treeline on all aspects but is most likely on NW to SE aspects due to recent SW to W winds. Watch for firmer wind transported snow on varied aspects especially in areas of complex terrain.
New sensitive storm slab is most likely above treeline in areas that receive more than a few inches of rapidly accumulating snowfall.
The persistent slab problem has returned to the Northeast zone due to recent avalanches and some reactive tests on the Valentine's Day or 2/17 crust. Avalanches stepping down to these depths would be large and very dangerous.
Loose wet avalanches won't be listed in the northeast zone due to a plethora of avalanche problems but are likely in all zones on steep slopes near or below treeline during rain showers. Loose wet avalanches along the east slopes of the Cascades that begin small may become large by entraining deeper layers.
Cornices won't be listed as an avalanche problem but avoid travel on ridges near where cornices may have formed and avoid steep slopes below cornices that may fail at any time. Cornices have been reported as large and in charge in many areas. They will have likely been weakened during the recent storm cycle becoming more likely to fail.
The snowpack may remain reactive and dangerous on Saturday and is only beginning the spring stabilizing process. Higher precipitation intensities could trigger avalanches. Avalanches may step down or entrain deeper layers and be large and dangerous especially if they reach the Valentine's Day crust layer.
Backcountry travel in avalanche terrain above treeline is not recommended on Saturday. Careful snowpack evaluation and cautious routefinding will be required in other areas.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC and NRCS stations indicate about 2 feet of snow in the northeast Cascades with less elsewhere along the Cascade east slopes.
A strong frontal system brought increasing precipitation and winds along with a warming trend to the Cascades on Thursday. On Thursday night rain may have pushed up to about 4000 feet in the northeast Cascades and about 5000 feet in the southeast Cascades. By Friday morning NWAC stations along the Cascade east slopes had about .35-.9 in of WE  with only 0-5 inches of snow mainly in the northeast Cascades.
The snow and avalanche conditions are rapidly changing in the Olympics and Cascades!
Recent Observations
North
On Wednesday, the NCMG on Delancey Ridge observed crowns from recent natural storm slabs about 20-30 cm deep on S-SW aspects near and above 5500 feet. In a test pit on a SE aspect at about 5400 feet, the 2/17 melt freeze crust gave hard but sudden planar results in compression tests failing on facets above the crust.
The NCMG were out again on Thursday near Washington Pass and report a 2/17 crust and the Valentine's Day layer at about 80-130 cm down. Deep tap tests of the Valentine's Day crust at 95 cm on gave results 1 out of 4 tests; PSTs gave results that ranged from no result to PST End so there is variation in the reactivity of the Valentine's Day layer.
Central
Mission Pro-patrol reported surprisingly minor results during avalanche control Thursday morning despite the new snow and moderate west winds. The new snow was generally bonding well with only a few areas of soft wind slab releasing below ridge-lines. The releases were shallow and did not step down to any deeper layers. Â
South
No recent observations.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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Very 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
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2