Avalanche Forecast

Sunday promises to be a tricky and potentially dangerous day after a long period of low avalanche danger, especially in the Paradise area. Locally lower danger may exist in the Crystal/White Pass portions of the SW zone. Building storm slabs may release on a variety of interfaces on all aspects. Choose conservative terrain and look for increasing signs of instability as snow levels rise and winds and precipitation increase during the afternoon and evening.   

A complex storm system will bring increasing rain and snow, rising snow levels and W-SW winds on Sunday.  See the mountain weather forecast tab for more details, but in general more warming is expected in the SW Cascades (Crystal, Paradise, and White Pass) with a slower transition to rain at Stevens and Snoqualmie Passes and at Mt. Baker. The heaviest precipitation is forecast for the Stevens and Snoqualmie Pass areas through the afternoon on Sunday, with further moderate to locally heavy precipitation expected in all areas Sunday night.  

New snow will build upon the light amounts of new snow received Friday night. New storm and wind slab may fail at a few different interfaces; within unstable new storm layers caused by the rising temperatures and increasing precipitation rates, at the recent snow/new snow interface or down to the previous snow surface comprised of various crusts or weak persistent grain types. We want to highlight that storm slabs may be touchiest in the Stevens Pass area where persistent weak layers have been preserved by Friday night's snow and exist at a variety of elevations and aspects. The later transition to rain forecast for the Stevens Pass area on Sunday will also build locally deeper slabs. 

Strong winds will quickly build unstable wind slab on lee slopes at higher elevations Sunday. 

Natural loose avalanches will release on steep slopes of all aspects in areas/elevations that see a switch to rain. In areas that receive more snowfall before the transition, expect the potential for loose wet avalanches to entrain more snow. Be especially careful of loose wet avalanches around terrain traps. 

Remember that beneath any new snow received during this storm, a myriad of early season terrain hazards exist, especially at lower elevations. Expect terrain hazards with poorly covered rocks, vegetation and creeks, particularly on south-facing terrain, at lower elevations, and on exposed ridges where wind events have stripped much of the seasons snowcover.

After 12 long days of high pressure, the first frontal system in awhile crossed the Cascades Friday morning. It wasn't much of a front as the high pressure weakened it significantly, with only a brief period of light rain and snow. Localized snow showers continued Friday night. New snow accumulations ranged from 2-5 inches along the west slopes of the Cascades with a local maximum at the top of Alpental with 8 inches of new snow.

Below this most recent storm snow, a highly varied array of surface snow conditions exists, including melt-freeze crusts, settled old storm snow, and a mix of recently formed surface hoar or near surface facets (sugary snow) at lower elevations and some shaded terrain. 

The overall snowpack of 2-5 feet along the west slopes is stable with settled old snow sitting over the strong Thanksgiving rain crust, buried about 1.5-2.5 feet.

Observations

North

On Wednesday, NWAC Pro Observer Jeremy Allyn was on Green Mountain and found settled, stable snow conditions. At the summit, northeast slopes were wind affected, but there was no snow available for transport. At peak solar warming, spring-like conditions were found on steep solar aspects. There was little to no snow below 5000 ft. 

Central

There is a pertinent observation from the Yodelin area of Stevens Pass from Friday detailing recently buried surface hoar in an open location below treeline on the NWAC observations page.

Alpental pro-patrol reported sensitive but shallow 4-6" storm slabs during Saturday morning's avalanche mitigation. The storm slabs were easy to trigger but did not run far. Wind transported snow was noted near-treeline from N-NW winds Friday night.

On Wednesday, NWAC Pro Observer Jeff Ward was on Jove Peak where he found little to no avalanche concerns. He found a mix of conditions, ranging from corn-snow on solar slopes, to powder on lower angle slopes at lower elevation, and large (1 cm+) surface hoar in the valleys.

South

Professional observer Jeremy Allyn was in the Crystal backcountry on Saturday.  He found variable snow with pockets of enjoyable dust on crust in smoother terrain. Very localized pockets of soft wind slab were unreactive. Plenty of early season terrain hazards exist on solar aspects, wind scoured terrain and at lower elevations.