Avalanche Forecast

Another strong warm front is expected Tuesday. Strong southwest to west winds near ridges and increasing moderate to heavy rain or snow at further warming is expected through the day Tuesday.  

More newly forming or increasingly large persistent, storm or wind slab will continue to be the focus on Tuesday along the east slopes. 

The warming and change from snow to rain may have already caused a widespread natural avalanche cycle by the time Tuesday's storm arrives, however where still snowing this should reload new slab layers over the strong November crust. 

Note that the east slopes still do not have a uniform snowpack, though with each storm, snowdepths are beginning to even out by elevation band and from north to south. 

Continue to be aware of the potential for dangerous persistent slabs, produced by weather in late November. Persistent slab is especially dangerous because it may be harder to trigger and propagate rapidly causing larger faster moving avalanches. Also, shallower storm slab avalanches may step down to the persistent slab, releasing potentially large and dangerous avalanches.

Dangerous persistent slab should still be expected on Monday. Persistent slab may be human triggered where persistent weak layers have been buried intact especially in the northeast and north central zones. Stay on low angle slopes and watch and listen for clues like shooting cracks and whumping and use caution until these layers are known to have stabilized.

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 are generally in the 1-6 foot range along the east slopes with the most in the northeast zone and the least at Blewett Pass and in the southeast zone. However, strong storms over the past few days have been 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, especially Monday.

This weather and snowpack scenario should put all on alert as this is a pretty classic PNW avalanche recipe!

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.

So the mid November crust and late November facets and hoar frost should still be reactive to upcoming loading by rain and snow.