Avalanche Forecast

A weak disturbance is expected to bring clouds and light snowfall across the forecast area overnight Thursday, decreasing Friday. Only light amounts of new snow are expected and should not cause an increase in danger. Moderate NW winds at higher elevations may continue to transport available snow, building areas of wind slab on a variety of a-typical aspects from east to southwest facing. 

While the overall danger should continue to decrease, continue to travel with caution and watch for any slab like structure or cohesion in the upper snowpack, indicating the possibility of slab avalanches propagating.   

Watch for touchy recently formed cornices and keep a safe margin along ridges and slopes below.

Most areas now have deep unconsolidated recent storm snow and this has created a non-avalanche, snow immersion, tree-well hazard in places. Keep partners in sight at all times when traveling in terrain with deep unconsolidated snow.

Recent deep storm snow has been settling and stabilizing Wednesday and Thursday under fair cool weather. This has allowed for storm related weak layers to settle with no storm slab avalanches reported since Tuesday.

Moderate to strong northerly crest level winds have been transporting snow on many exposed ridges both Wednesday and Thursday. This should have built areas of wind slab on a variety of aspects, including non-typical southerly facing slopes near and above treeline.

Numerous field obs Wednesday and Thursday indicate the previous very sensitive storm layers have settled and continue to stabilize. Cooling temperatures and light winds have left a favorable storm snow profile of increasing density with depth and some fabulous skiing and riding conditions. 

The old snow interface formed during the high pressure in early December and buried 12/15 appears to be favorable as well, from observations received Wednesday and Thursday.

The main take away is the current upper snowpack in most areas near and below treeline, away from ridges and wind transport, remains of low cohesion and lacks the structure to support slab avalanches. Wind and warming and just some surface settlement can change that structure however, so continue to watch for changing surface snow conditions. 

The total storm snow Sunday through Tuesday night ranged from 2-4 feet in the west slope zones and Cascade passes. Light showers at cool temperatures with light winds Wednesday added 1-3 inches additional new snow.

One or more widespread natural avalanche cycles have occurred during the heaviest intensities, especially Tuesday. Sensitive storm slab avalanches occurred Tuesday throughout the range up to size 2 from natural, human and explosive triggers. These avalanches all appear to have released within storm layers with a few exceptions from explosive trigger possibly stepping to the late November rain crust, but not confirmed. 

There's plenty of great snow at mid and lower elevations, so eliminating any potential wind loaded terrain may be the best plan. 

The recent storm has formed touchy cornices along ridges, so stay clear of cornices.

Observations

North

Reports Wednesday from snow safety at Mt Baker indicate the storm related sensitivity Tuesday has settled as of Wednesday, however not disappeared. There was a 2 foot human triggered slab release that propagated about 45-75 feet wide near ridgeline. Extensive active wind transport was visible on Shuksan and higher exposed peaks above treeline midday Wednesday, as northerly winds increased at crest level. 

On Tuesday morning the Mt Baker pro patrol reported widespread triggered storm slab, up to about 12 inches, some large, and continual natural avalanches to below treeline. 

Central

Multiple backcountry reports from NWAC observers at Alpental and Crystal Mountain Wednesday and again Thursday confirm that storm weak layers continue to settle and stabilize. No triggered or natural avalanches were reported Wednesday with cold low cohesion storm snow well connected to the 12/15 interface. The storm snow is deep out there! generally 2-4 feet in these central zones from Stevens to Mt Rainier.

There were touchy cornices reported in the Crystal backcountry Wednesday. Dropping several cornices did not release any avalanches on slopes below.  

On Tuesday the Alpental pro patrol also reported widespread natural and very touchy 8-12 inch storm slab at all elevations due in part to a weak storm layer buried about at 8 inches. This included very long distance sympathetic releases and at least one release possibly due to vibration of the chair lift!

Touchy storm slab at Alpental on Tuesday December 19th. Photo John Stimberis

South

No recent observations.