Avalanche Forecast
Regions: Cascades - East.
The recent snow and conditions observed Friday warrant patience and caution on Saturday. Don't step out into aggressive terrain before new or recent snow layers have had a chance to stabilize.
Detailed Forecast
A change to strong WSW winds at higher elevations and cooling should be seen along the east slopes of the Washington Cascades Friday night following the front. This area should get about 2-8 inches of new snow with a cooling trend by Saturday morning. Some areas especially at lower elevations will initially warm as cooler air gets replaced by milder air from the west.
The recent snow and conditions observed Friday warrant patience and caution on Saturday. Don't step out into aggressive terrain before new or recent snow layers have had a chance to stabilize.
New storm slab from Friday night or lingering storm slab should continue to be the most widespread avalanche problem Saturday. Ratchet back your plans if you see signs of storm slab such as touchy hand shears or results on test slopes.
With recent varied or WSW winds and stronger WSW winds Friday night new wind slab will be likely.  Avoid lee slopes with these aspects especially if you see signs of firmer wind transported snow.
There remains significant deep, soft snow out there from the past week. Unconsolidated snow, particularly around small trees, can present a non-avalanche, snow immersion hazard. Keep visual and verbal communication with your travel partners when traveling in treed terrain.
Keep the 12/15 crust/PWL interface in the back of your mind as we progress through this storm cycle and determine whether loading awakens any pockets of deeper instabilities.Â
Also despite all this new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.
Snowpack Discussion
We are at the tail end of a couple of days of very active changeable complex weather. On Thursday strong westerly flow aloft carried a very moist occluded front across the NW. On Friday a moderately deepening low pressure system is crossing the Cape Flattery area and a strong cold front will cross the Northwest Friday evening. This means a variety of upper snowpack conditions could be found by late Friday on the Cascade East slopes.
By Friday morning NWAC and NRCS station along the Cascade east slopes had about 3-8 inches of new snow that fell with an overall slight warming trend. Winds on Friday have been generally moderate to strong WSW at higher elevations.
Regular though usually light snow also accumulated along the east slopes of the Washington Cascades with cold temperatures as very weak weather disturbances crossed the NW in about the past week.Â
About 1.5 to 3 feet of recent snow sits atop the 12/15 crust/persistent weak layer interface in the Washington Pass area and in the central-east Cascades near the Cascade crest. Comments from professional guides in the Washington Pass area are included below that help reduce uncertainty surrounding the 12/15 crust/persistent weak layer interface.Â
Snowdepth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger.Â
Observations
North
The NCMG were in the Washington Pass area on Friday and observed moderate snow, warming and very touchy storm slab of 15-25 cm. Several naturals were seen to size 1.5 and several other crowns were seen in steep unsupported terrain. Poor bonds were found in upper snow layers via numerous hand shears and on test slopes.
A summary of previous professional guide reports regarding persistent weak layers for the Northeast zone including Washington Pass:
- In the above treeline zone, small faceted grains are rounding and gaining strength, down 70 cm and below the storm snow that accumulated starting 12/15. They have not been reactive in snowpack tests.
- The upper snowpack on solar aspects near treeline are bonding well to a strong solar crust buried on 12/15. However, they cannot rule out buried surface hoar in some sheltered larch glades around 6000 feet.
- Below treeline, surface hoar that was buried on the 12/15 crust is down 70 cm in flat meadows and creek valleys, but has yet to be found in avalanche terrain.
Central
No recent observations
South
No recent observations
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: 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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1