Avalanche Forecast

Cool weather with mostly clear skies or high clouds are expected Thursday with moderate NW winds at higher elevations. 

This weather will continue to cause a decreasing trend in the avalanche danger as recent storm snow slowly stabilizes. At higher elevations, expect wind transport and building areas of wind slab, mainly above treeline and onto unusual aspects from the mostly NNW winds.

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

Watch for touchy recently formed cornices and avoid travel on steep unsupported slopes.

Remember that beneath snow received during this storm cycle, 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 season's snowcover.

A strong storm cycle began Sunday and tapered Tuesday night. Storm total new snow ranges from 2-4 feet as of Wednesday morning along the east slope zones, very similar to west slope zone storm snow amounts.  Light showers at cool temperatures with light winds Wednesday added little 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 from natural, human and explosive triggers. 

It remains uncertain if the majority of these avalanches released within storm layer weaknesses or at the 12/15 interface potentially involving buried surface hoar or near surface facets formed during the high pressure in early December.  

Cooling temperatures and light winds have left a favorable storm snow profile of increasing density with depth. 

The old snow interface of 12/15 remains uncertain with limited observations from Wednesday. Caution remains the watchword due to low confidence of the extent and distribution of this potential weak layer.

The main take away is the current upper snowpack in most areas near and below treeline, lacks a slab structure and remains of low cohesion. Thus, there is low propensity to release slab avalanches. However, it may only take some minimal wind effect to stiffen the surface snow to change all that.

Crest level winds have shifted and strengthened from the north Wednesday, no doubt transporting the abundant new snow and building wind slab layers on a variety of aspects, especially above treeline.  

The snowpack above treeline may be very different as there are likely wind slabs lurking. Limited observations above treeline means a lower confidence on the forecast and hence travelers should approach with a high margin of safety. 

There's plenty of great snow at mid and lower elevations so eliminating any potential wind loaded terrain would be wise.

Observations

North

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.