|Travel Advice||Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.||Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.||Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.||Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.||Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.|
|Likelihood of Avalanches||Natural and human-triggered avalanches unlikely.||Natural avalanches unlikely; human-triggered avalanches possible.||Natural avalanches possible; human-triggered avalanches likely.||Natural avalanches likely; human-triggered avalanches very likely.||Natural and human-triggered avalanches certain.|
|Avalanche Size and Distribution||Small avalanches in isolated areas or extreme terrain.||Small avalanches in specific areas; or large avalanches in isolated areas.||Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.||Large avalanches in many areas; or very large avalanches in specific areas.||Very large avalanches in many areas.|
By far the most common problem is related to recent snow on top of the prominent crust layer. The 16+ inches that Turnagain Pass received on February 7th have been responsible for many reported avalanches since that storm. The general trend of these avalanches is – small in size (12-20″ deep), lower volume, decent propagation across wind stiffened steep slopes. Check out the observations page for a bunch of photos from the last 6 days, and this observation for a good quick synopsis of the problem.
The 2 properties necessary to create avalanches that are not always found –
1. A cohesive slab – some wind loading and stiffening is necessary to create connectivity of the surface snow, otherwise it’s just loose powder with sluff potential.
2. A faceted interface between the new snow (Feb 7th storm) and the underlying crust (January melt/freeze) or old snow. In places where the facets are present, this is a significant weak layer consisting of large loose grains with poor bonding.
Cold high pressure from early in the week has transitioned to a showery precipitation pattern as of yesterday afternoon. A few inches of fresh light powder have fallen since Wednesday. Temperatures remain quite cold, especially for snow to be falling, reaching into the negatives at many of our local weather stations. Wind is generally light, although since about 4am the wind has increased slightly and switched over to a East Northeast direction. Expect cloudy skies today with snow showers and 2-4 inches of snow accumulation today.
The extended forecast looks like more of this same pattern. A low pressure system is anchored over the northwestern gulf, and expected to stay there well into next week. Most precipitation from this event will be showery, but there is a chance for heavier snow events by the weekend.
|12/01/23||Avalanche: Sunburst||John Sykes Forecaster|
|12/01/23||Turnagain||Observation: Eddie’s trees||Anonymous|
|12/01/23||Turnagain||Observation: Turnagain – God’s Country||Graham Predeger Forecaster|
|11/30/23||Turnagain||Avalanche: Tincan Trees||Kakiko Ramos-Leon|
|11/27/23||Turnagain||Avalanche: Tincan Ridge||Schauer/ Stiassny Forecaster|
|11/26/23||Turnagain||Observation: Road report: Slide with dirt on Repeat offender||Anonymous|
|11/26/23||Turnagain||Observation: Pete’s North||Ben Sullender|
|11/25/23||Turnagain||Observation: Tincan trees||John Sykes Forecaster|
|11/21/23||Observation: Spokane Creek||John Sykes Forecaster|