Avalanche Forecast

A cold and dry forecast Thursday with increasing clouds in the afternoon should do little to change the current avalanche danger.  Isolated new wind slab may have formed above treeline, mainly on lee easterly aspects. 

A more interesting and dangerous avalanche setup will occur late Thursday night but mainly on Friday as moderate to occasionally heavy precipitation loading occurs along with rising snow levels and strong winds Friday.  This storm will likely test the strength and bonding of the near surface weak layers as well as introduce new snow instabilities. 

The last major storm to impact the mountains occurred over Thanksgiving weekend. This storm produced heavy rain followed by an arctic air mass that settled over the region along with 1-2 feet of low density snow at sites near and west of the crest. Little avalanche activity was seen following the storm due to the cooling, good bonds to the newly formed early December crust, lack of wind and generally cohesionless new snow.

Dry, cold and locally windy weather followed during the first week of December. This produced local wind slab and scoured surfaces in exposed areas, and hoar frost and near surface faceted snow in sheltered areas. 

2-9 inches of wet snow was seen late Thursday to Friday morning with the most at Paradise. This produced some more 6-12 inch skier triggered storm slab releases at the Mt Baker ski area on Friday and some shallow storm slab around Mt Hood Meadows.

Warming began last Friday and continued through mid-day Tuesday on both sides of the Cascade crest and Mt. Hood.  Wet loose avalanches, roller balls, pinwheels and shallow wet snow conditions were reported during this time.  New information from an off-duty patroller from Crystal mountain are of a wet loose avalanche that stepped down to the ground Monday.  The slide likely stepped down on a pocket of depth hoar found near rocks and shallower snow cover.

The warming also eliminated the strong temperature gradient that was in the upper snowpack. However this favorable temperature regime did not completely eliminate the most recent weak layers in the upper snowpack.  Stevens Pass DOT avalanche professionals reported faceted layers surviving below crust interfaces (including the early Dec crust 30cm down) and easy compression test releases. 

Light snowfall accumulations, generally 1 or 2 inches, with up to 5 inches fell near Mt. Baker Wednesday with moderate W to NW winds. This likely built some shallow new wind slab on lee easterly slopes above treeline.  A significant cooling trend was in process Wednesday afternoon and should continue into Thursday. 

Shallow snow cover is limiting the avalanche danger at lower elevations.