Wind slabs and cornices will be the main concern today as warm temperatures and a quick moving system rolls through. Ridgetop winds bumped up into the ‘strong’ category overnight from the east. With only a few inches of new snow accompanying the wind, fresh slabs should be shallow and less than a foot thick. Between 1-4″ of snow fell last night at the upper elevations and another 1-3″ is expected today. There is little old loose snow available for transport due to the strong winds last weekend, hence new slabs should be mainly composed of the new snow. Rain falling up to 1,800′ will limit slab development in the mid-elevations.
Evaluating surface conditions will be key if venturing into the backcountry. Look for loading patterns, i.e. is the slope cross-loaded or top-loaded? Watch for shooting cracks and listen for hollow sounds. These are signs of hard snow over softer snow and indicate wind slab potential. Wind slabs could be stiff enough to allow a person onto them before releasing. Old slabs could still be reactive as they may be sitting on weak snow underneath (near surface facets and surface hoar).
Cornices: The warming temperatures at the upper elevations can help destabilize cornices. Not only can they break farther back than expected, they may be more tender today and could also trigger a slab avalanche on the slope below.
Old natural wind slabs on Raggedtop in the Girdwood Valley. Triggered by cornice falls likely last Sunday, 1/13.
South of Turnagain – Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas and strong winds over the weekend loaded leeward slopes. Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as concerning facet/crust combinations in the bottom of the snowpack. If you’re headed this way, evaluate terrain exposure and the snowpack as you travel. Be on the lookout for signs of instability and be suspicious of any wind loaded slope.
Many glide cracks are covered with recent snow/wind and may be hard to spot. Remember the known areas with cracks are Eddies, Tincan, Sunburst, Magnum, Cornbiscuit, Lipps, Seattle Ridge, Johnson Pass, Lynx Creek, Summit Lake, Petersen Creek, and Girdwood. Avoiding/limiting time under these features is prudent as they can release into an avalanche at any time and are completely unpredictable.
Yesterday: Mostly clear skies were over the region with clouds and light snow/rain moving in overnight. Between 1-2″ of snow has been seen at the mid-elevations. The rain/snow line is hovering between 1,500 – 1,800′. Ridgetop winds increased overnight and are blowing in the 30’smph this morning with gusts near 50mph from the east. Temperatures are warm, upper 20’s to 30F along ridgelines, upper 30’s at 1,000′ and 40F at sea level.
Today: Mostly cloudy skies with light rain/snow showers are expected. Only 1-2″ of new snow should fall in favored zones with light rain below 1,500′. Ridgetop winds are expected to stay strong, 20-30mph with gusts to 50mph from the east. Temperatures should also stay warm with ridgelines reaching 30F and sea level 40F.
Tomorrow: Clearing skies and decreasing winds are on tap as the system over the area today moves out. Mostly sunny skies are expected to last through Friday and possibly into the weekend.
*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||33||1||0.2||53|
|Summit Lake (1400′)||29||1||0.1||21|
|Alyeska Mid (1700′)||32||0.5||0.2||50|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||30||*N/A||*N/A||*N/A|