Avalanche Forecast

The strong warm front that has caused heavy rain most of Tuesday is expected to pass by early Wednesday with cooling and a period of light to moderate precipitation along with continued strong winds.

Further cooling and lighter showers are expected later Wednesday with strong southwest winds shifting to strong westerly winds.

This weather will cause a transition in the snowpack from wet and saturated surface layers to a draining and gradually refreezing upper snowpack. Cooling should change rain to snow by Wednesday to gradually lower elevations. New shallow snow should begin building on the refreezing snowpack. This transition should form a good bond of new snow to the forming crust.

Continued strong winds are likely to transport new snow and begin forming some wind slab layers on lee slopes below ridges by later Wednesday. 

It is likely that the problem associated with the recent persistent slab conditions overlying the November crust have abated through avalanche release or the draining rain through the upper snow layers. However, until the upper layers solidify and refreeze we can't be fully sure we can rule it out. While now significantly less likely to release, continue to be aware of the potential for a persistent slab in many areas along the east slopes. Persistent slab is especially dangerous because it may be harder to trigger and propagate rapidly causing larger faster moving avalanches.

With less snow below treeline, wet loose snow avalanches will not be in the forecast. But change your plans if you find wet snow deeper than a few inches or see signs of wet loose activity such as pin wheels or natural wet loose avalanches.

Weather and Snowpack:The northeast and north central Cascade zones have the deepest snowdepths found throughout the Cascades this season thanks to cold air pooling on the east side in otherwise warm storms for the west. 

Snowdepths along the east slopes are generally in the 1-5 foot range with the greatest snowdepths in the northeast zone and the shallowest near Blewett Pass and in the southeast zone. However, strong storms Sunday and Monday were heaviest along the south, so snowdepths are beginning to even out from north-south.

We had a wet and wild November and this formed a strong crust by mid November in all areas.

A long stretch of cold weather led to widespread near surface faceting and surface hoar formation along the east slopes in late November.

The weather so far in December has become very active with periods of heavy snowfall over the past week with an overall warming trend Monday, culminating in a downpour of rain all day Tuesday at high freezing levels.

This weather and snowpack scenario caused ripe avalanches conditions, though few reports have been received as it hasn't been the most pleasant of conditions over the past few days.

Reports:

The most important report for along the east slopes comes from Mission Ridge Ski Area on Sunday where the pro patrol reported numerous and often sympathetic easily triggered slab avalanches of about 8-16 inches releasing on a rain crust from early December. One very large explosively triggered slab avalanche on the northeast slope of Windy Ridge was 5 feet deep and propagated several hundred feet which released on the mid November crust.

Increasingly large persistent and storm slab conditions were found in the Smith-Brook area. just east of Stevens Pass Sunday by NWAC's Dallas Glass. These conditions may be susceptible to natural avalanches with additional loading or a change to rain, possibly before the next storm arrives Tuesday!

NWAC observer Jeff Ward was at Washington Pass on Friday and was surprised by the lack of activity on the potential PWL and considered the conditions uncertain.

With varying amounts of rain received along the east slopes Tuesday, it is still too early to tell the current state of that persistent slab problem and how it has or has not changed. This layer may still be reactive, though likely less so now following the rain event. Still best to proceed with caution until more definitive observations come in.