Avalanche Forecast

Tuesday should see the beginning of another extended dry period. Initially on Tuesday freeing levels should be very low with cool air in place following Monday's frontal passage. Winds should diminish to generally light on Tuesday.

This weather should allow for the beginning of recent unstable conditions to settle and slowly stabilize. However, this process my take some time in certain areas, such as higher terrain and where significant wind slab has formed below ridges. 

While the overall trend is for lowering danger, triggered avalanches should remain likely in the alpine elevations and possible in the near treeline band. 

In areas with light wind, where rain changes to snow, and with lower rates of loading, the cooling trend should help bond new snow to old snow and help build right side up conditions with lower density snow nearer the surface. This can mean some good skiing in those types of areas. Underlying wet snow should also begin to refreeze and strengthen.

Shallow snow cover and shallow new snow will continue to limit the avalanche danger at lower elevations.

Remember this is a regional forecast and you must make your own on site evaluations to see if they are different than forecast.

Warm wet weather the weekend of 14 and 15 December created another crust layer in most areas. This seems to have capped and stabilized underlying hoar frost and faceted snow and made those layers generally unreactive.

Cold weather, light amounts of low density snow and some surface hoar formation were generally seen mid-week last week.

This set the stage for warmer wet weather that arrived Friday and over the weekend, culminating with a cold frontal passage Monday afternoon. A warm front moved across the Northwest Friday. This generally caused strong southwest winds, increasing moderate to heavy snow and greatly warming temperatures. Another warm front moved across the Northwest on Saturday night and Sunday. This generally caused strong northwest winds and wet snow or rain at further warming temperatures. NWAC sites near and west of the crest for the 48 hours ending Sunday morning had ended up mostly with about 4-17 inches of very wet heavy snow.

Another round of wet heavy snow began overnight Sunday through Monday afternoon depositing another 4-10 inches as of Monday afternoon. The most recent heavy wet snow has also been accompanied by strong west to northwest crest level winds. NWAC Weather stations at the top of Crystal Mountain and Mission Ridge recorded peak gusts to 79 mph and 99 mph respectively Monday afternoon! 

The warming, dense or wet new snow and strong winds have combined to build both unstable storm slab layers as well as sensitive wind slabs by Monday afternoon, especially in the alpine elevations.

The most pertinent report Monday was from the pro patrol at Mt Baker Ski area where new sensitive wind slabs were releasing full paths with many natural slides reported including a rather large release from Table Mountain running to the Bagley Lakes valley floor. Some slides were releasing sympathetically as well with most wind slab crowns ranging from 30-60 cm (1-2 ft).

There was also a report of a wet slab release Sunday midday in the Alpental Valley below Chair Peak that ran a significant distance. Poor visibility precluded the view of starting zone elevation but a crown depth was estimated over 30 cm. As of Monday, additional heavy dense loading has occurred in that area and should maintain a heightened interest for anyone thinking about travelling in steeper terrain for a few days.   

Other recent observations: An NWAC observer just east of Stevens Pass on Saturday reported that the recent snow gave some cracking and small wet loose avalanches. The Mt Hood Meadows ski patrol Saturday and Sunday reports a stable freezing rain crust at least to 7300 ft but it is unknown if this condition extends very far around the mountain.

Shallow snow cover has been limiting the avalanche danger at the lowest elevations.