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.

There remains much uncertainty regarding a persistent slab problem throughout this zone, so avoiding larger terrain of consequence will be the best travel plan until a clearer picture emerges.  

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. 

There remains uncertainty about the new snow, old snow interface buried 12/15 as there was extensive surface hoar and near surface faceted snow prior to the storms arrival, mostly in terrain below 6000 feet. This potential layer should give pause when considering bigger terrain. 

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 east slope zones, similar to the west slopes. 

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 appear to have released within storm layers, but not entirely confirmed. 

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

Observations

North

Observations from Wednesday and again Thursday along Delancy ridge indicated storm layers continue to settle and stabilize, However, there was evidence of the strong northerly winds forming wind stiffened snow and wind slab near treeline, limiting travel to high terrain with obvious wind slab problems.

The NCMG  passed on information to the NWAC for the Washington Pass and Holden area for Tuesday. In summary several large natural avalanches were seen and skiers were triggering very touchy storm slab which in some cases was stepping down to about 60 cm to a rain crust from Monday December 18. It was uncertain if the December 16 buried surface hoar or faceted snow was present.

On Sunday, a NCMG group found surface hoar buried intact up to 6000' in the Washington Pass area by 10-15 cm of recent snowfall. No signs of recent avalanche activity were noted. 

Central

The Mission pro patrol on Wednesday reported no avalanches with much of the snow stripped from ridges during the storm Tuesday.

The Mission pro patrol on Tuesday reported new 6-10 inch wind slab on specific lee east slopes above about 6400 feet. No avalanches were triggered but the wind slab was not bonding well to previous snow. Other windward slopes were scoured.

South

No recent observations.