Avalanche Forecast
Regions: Cascades - North East.
An avalanche cycle may begin Wednesday night and stretch into Thursday morning. Wet snow avalanches are more likely below 6000 feet and may entrain new snowfall. New storm or wind slabs are likely above 6000 feet. Allow the snowpack to stabilize and generally avoid travel in avalanche terrain Thursday.
Detailed Forecast
In the northeast zone, an avalanche cycle may begin Wednesday night and stretch into Thursday morning with peak warming along the east slopes expected Thursday morning. A slow cooling trend with light showers heading into Thursday afternoon should start to decrease the avalanche hazard.
Wet snow avalanches are more likely below 6000 feet and may entrain new snowfall received Wednesday and Wednesday night or break into deeper layers from the 2/8 - 2/10 storm cycle. New storm or wind slabs are likely above 6000 feet due an increasing temperature trend overnight.
Allow the snowpack to stabilize and generally avoid travel in avalanche terrain Thursday. Â Â
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Snowpack Discussion
Weather and Snowpack
The 2/8 - 2/10 storm cycle deposited 2-3 feet of snow in the Washington Pass area. In the central-east and southeast zones a rain crust formed with shallow amounts of new snow following at the tail end of the cycle. This storm cycle was a great test for any Persistent Weak Layers buried deeper in the snowpack. There was no evidence of any deeper releases and as a result, we have removed Persistent Slab from the problem list.
High pressure Saturday to Tuesday brought increasing sunshine and warming temperatures. Temperatures reached the 30's and 40's in many areas along the Cascade east slopes. This caused snowpack settlement, some small loose wet avalanche activity and a decreasing avalanche danger.
Another atmospheric river impacted the PNW on Wednesday. Light to moderate rain and snow with high snow levels occurred along the east slopes of the Cascades with localized freezing rain along the lower east slopes. Through 5 pm Wednesday, using the NWAC and NRCS Snotel networks, the southeast zone likely saw rain up to 7000 feet, 5000-6000 feet in the central-east and reports from Mazama indicated that it was still snowing in the valley. Washington Pass may have started off as freezing rain early Wednesday morning before a switch to snow.Â
Recent Observations
North
A report via the NWAC Observations page indicates a shallow climax slab avalanche on a north slope on Mt Patterson near Winthrop on Sunday. There is likely to be shallow faceted snow in this low elevation area.
NWAC observer Jeff Ward was out in the Silver Star and Cedar Creek drainages with NCH on Monday and reported minor loose wet avalanches on solar slopes and no other activity or signs on instability. Snow was still cold on north slopes in the 5000-9000 foot range.
Jeff was out again at Washington Pass on Tuesday and reported that slopes were cooler due to cloud cover with no signs of instability or avalanches.
Central
NWAC's Tom Curtis travelled in the Icicle Creek area near Cashmere Mountain Saturday 2/11. Tom did not get far as there was only a dusting of recent snow over a slick, firm crust. The greatest danger in this area was from uncontrolled falls on the slick crust as opposed to avalanches.Â
Another report via the NWAC Observations page for Dirty Face Peak for Sunday indicates that wind slab was unreactive there on Sunday.
Reports from the Mission Ridge pro-patrol mostly indicate a breakable surface crust from late last week and poor ski conditions Sunday and Monday.
South
No recent observations.Â
Avalanche Problems
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: Very 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: 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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1