Avalanche Forecast

Cooling overnight Friday with light rain showers changing to light snow showers. Showers should end by midday Saturday with further cooling and light winds.

Where surface snow was wet, a newly forming surface crust will begin forming with only light amounts of fresh snow expected above. This should not lead to an overall increase in danger.

At mid and lower elevations where freezing rain occurred, shallow new snow should bond well to the extensive freezing rain crust. 

Light snowfall and higher winds may occur at the upper elevations in the above treeline band. As snow begins to accumulate Friday night and early Saturday, keep watch for developing wind slabs on northerly to easterly facing slopes, mainly if greater new snow is received than forecast.

Be cautious when travelling on slopes with an exposed slick surface crust due to fall hazard, mainly mid and lower elevations. 

Uncertainty still exists surrounding extent and sensitivity of the persistent weak layer in the Blewett Pass and Mission Ridge areas. The precipitation event Friday will not be enough to test this basal layer with significant weight. Evidence and observations on this weak layer can be difficult to come by. Be prepared to adjust your travel to respect this low likelihood/higher consequence problem.

Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

A mix of precipitation types fell overnight Thursday and through the day Friday. Extensive freezing rain fell at mid and lower elevations along the east slopes as well as in the Stevens and Snoqualmie Pass areas. This significant freezing rain event has likely destroyed or capped a variety of existing snow surface forms. The newly formed crust is limiting the current avalanche potential and formed over a relatively strong older snowpack. 

Recent mild weather, especially at higher elevations, has allowed for the strengthening of lingering wind slabs and upper snowpack weaknesses. Small isolated winds slabs have still been observed, however the extent of this problem continues to decrease.

Precipitation types above treeline during the current storm cycle have been unobserved. Therefore, the upper elevation extent of the freezing rain crust are not well known at this time. There may have been a mix of rain or moist to wet snow in the upper elevations, and travelers should use caution and assess surface snow conditions carefully in higher terrain. 

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. 

Observations

North

North Cascades Mountain Guides were in the Washington Pass area on Tuesday. They found steep southerly and westerly aspects getting significant sun effect above 5,000 feet with surfaces a mix of moist and melt/freeze depending on timing. They also found up to 1 cm surface hoar in avalanche terrain below the inversion layer (up to 5,400 ft).

Central

A NWAC forecaster was in the Diamond Head area of Blewett Pass on Tuesday. Basal facets (2-3mm) were found above 5000' on NW-N-E aspects. Large column tests showed this layer was reactive and likely to propagate. However, varied surface roughness combined with an overall shallow snowpack made for a low likelihood of finding the right terrain to support an avalanche. Just like the nearby Mission Ridge area, this layer will need to be watched moving forward. 

Other pertinent observations from the area include a rain crust observed up to 5400 feet. Snowdepths were low in this area, making backcountry travel difficult at lower elevations, wind scoured areas, and on sunny aspects.

Mission Ridge Pro Patrol reported avalanche control work within the ski area Saturday produced 1-4 ft wind slab avalanches. The larger avalanches released to ground on 1 mm basal facets.

South

No recent observations