|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.|
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Triggering a large and unmanageable slab avalanche 2-4′ thick remains our primary concern. Yesterday, a snowmachiner remotely triggered two slabs on Seattle Ridge from a meadow below the slope; it’s important to remember that these avalanches can be triggered from the flats. These slabs were on the North end of the ridge above the powerline trail. This longtime Turnagain rider noted that avalanches in this area are not often seen. Additionally, similar slab avalanches were triggered in Girdwood Valley in the Notch Mtn area.
The avalanche activity yesterday was all in the mid to lower elevation bands. Various layers of old faceted snow sit under the 2-4′ of storm snow from Friday (photo of this below). The faceted layer has been overloaded by the new snow and is failing, creating the current ‘persistent slab’ avalanche problem. At the higher elevations, above 2,500′, the facets are not as pronounced, yet there are old layers of buried surface hoar that are a concern. How likely a slab is to be triggered in these weak layers at the higher elevations is uncertain at this time. Of note is very little to no traffic was seen in the upper elevation bands yesterday.
If you are headed out into the backcountry today things to keep in mind are:
Slab avalanches on East faceing Seattle Ridge (looker’s right of the up-track). Two of these could be the avalanches that were remote triggered from meadow below yesterday.
Loose snow sluffs on the West face of Magnum
Annotated photo of the storm slab bonding to the old snow surface, but the old snow surface is weak and failing. Hence, the new snow has ‘overloaded’ the older weak snow.
Three feet of new snow and wind effect on Tincan Ridge (left) and Seattle Ridge’s Repeat Offender and uptrack zone (right). It’s good to see the new snow, but slopes need time to adjust.
Turnagain Pass flats – plenty of safe places to play that are out of avalanche terrain. (Photo: Allen Garrett)
Cornices have grown and are suspect for breaking while traveling along ridgelines. Give these an extra wide berth and minimize any time below them. Cornice falls can trigger avalanches on slopes below.
Yesterday cloudy skies with light snow showers gave way to breaking skies in the afternoon. Total 24-hour accumulation was 2-5″ of low density snow in favored areas and no snow in others. Ridgetop winds were light to moderate from the East (5-20mph). Temperatures were in the mid 30’sF at sea level and in the teens along ridgetops.
For today, Sunday, a low pressure spinning East of us in the Gulf may push some moisture our way. Clear skies this morning are forecast to turn cloudy later today along with a chance that 1-3″ of light snow will fall. Ridgetop winds look to shift to the North and West and stay light (5-10mph) as we are on the back side of the low pressure. Temperatures will remain cool for March, in the mid 30’s again at sea level and teens along ridgetops.
Looking ahead to the work week, Monday another system passes through with a chance for snow followed by clearing and the chance for a nice day on Tuesday. Unsettled weather looks to continue later in the week.
*Seattle Ridge anemometer (wind sensor) rimed over and not reporting
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||28||4||0.4||93|
|Summit Lake (1400′)||24||0||0||36|
|Alyeska Mid (1700′)||27||3||0.2||82|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||23||*n/a||*n/a||*n/a|
|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|
|11/19/23||Turnagain||Observation: Magnum – PMS Bowl||Schauer/ Cullen/ Jonas Forecaster|
|11/19/23||Other Regions||Observation: Sunnyside/Penguin||Jose Ramos-Leon|
|11/19/23||Turnagain||Observation: Eddies||Andy Moderow|