Avalanche Forecast

Expect rapidly lowing freezing levels and an abrupt pattern change on Friday as a short round of rain and snow adds a shallow blanket of new snow on top of the highly variable existing snowpack. We'll be watching to see whether faceted crystals are preserved and buried as this round of precipitation moves through.

Snow accumulation and wind will combine to produce snow transport that should be marginally sufficient for wind slab or storm slab formation in the near and above treeline terrain, with insufficient accumulation below treeline. As a result of more extensive surface hoar growth and near surface faceting in these zones, these areas will need to be watched as new storm or wind slab is likely to be more reactive. 

With considerable uncertainty in the strength of the winds and new snow amounts and the spatial distribution of the potential weak layers and hard snow surfaces buried underneath, watch for signs of denser snow on top of settled powder or faceted crystals on non-solar aspects or increasing snow density on top of firmer melt-freeze layers on east through south aspects. With a lot of variety in the surface snow conditions right now and additional snow arriving through the weekend, Friday is an excellent day to submit an observation to NWAC to help us better define the extent of developing avalanche problems.

Early season terrain hazards have become an increasing hazard in recent days 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.

Strong high pressure has now been over the region since December 4th. Sunshine and very mild temperatures have been seen at higher elevations with steep temperature inversions and much colder temperatures accompanied by low clouds at lower elevations/valleys throughout the east slopes of the Cascades. The inversion top along the east slopes generally ranged from 4000-6000 feet during this time period. This weather has allowed for overall strengthening and consolidation of an already strong snowpack. Total snow consolidation along the east slopes of the Cascades ranges from 3-8 inches since December 3rd, with settled old storm snow of about 1 to 2 feet over the strong Thanksgiving rain crust.  East-side snowdepths are highest in the Washington Pass area and lowest in the southeast zone. 

No human-triggered avalanches have been reported in over a week. Some natural small loose wet slides have occurred on mainly steep sun exposed slopes over the last week, but have become much less frequent over the past several days. Active wind loading has not been observed since late last week. 

Surface conditions are highly variable. On solar aspects, surface melt-freeze crusts reform every night. On shaded and sheltered aspects, settled storm snow is still providing some nice skiing and riding conditions. Many aspects in higher terrain now feature wind stiffened snow. Near surface faceting and large surface hoar growth has been reported on colder, non-solar aspects, especially below the inversion. These persistent grain types will become important when snowfall returns and watched as potential future weak layers. 

Observations

North

NCMG was near Washington Pass on north-facing terrain on Wednesday and observed continued development of surface hoar (over 2 cm) below 6000 ft and faceting of the upper snowpack in thin rocky areas in the above treeline zone as well. They report no signs of instability in spite of increasing terrain coverage showing signs of wind effect.

NCMG was in the Washington Pass area on Monday and observed isolated pockets of wind slab to be generally unreactive.  No weak layers were noted in the upper snowpack and widespread and large surface hoar was observed near and below 6000' in non-solar, open terrain. 

Central

No recent observations.

South

No recent observations.