Wind slabs and cornices are the primary concern today above 2500′ due to recent strong winds and warm temps. Varying amounts of precipitation have fallen across the region this week, 4-6” in Turnagain Pass and 8-10” in Girdwood. Easterly winds (20-50mph) redistributed this snow by scouring ridges and loading slopes in the Alpine. These pillow-shaped wind slabs are visible on all aspects including cross-loading on windward aspects and top-loading on leeward aspects. Let’s not forget what this new snow may be resting on! Last week’s cold snap created very weak surface snow (surface hoar and near surface facets.) Wind slabs may be 1-2′ thick and sitting on isolated pockets of weak snow or connected across a slope.
Evaluating surface conditions will be key if venturing into the backcountry. A surface crust has formed in the mid and lower elevations due to rain the last few days and a slight cooling trend today. Once into the alpine look for loading patterns and feel for firm snow over softer snow. Be weary of hard supportable snow especially if it feels hollow or drum-like. Shooting cracks and whumpfing may not be present until a slab releases suddenly. Wind slabs could be stiff enough to allow a person onto them before releasing.
Cornices: Recent strong winds and new snow have added stress to cornices. Not only can they break farther back than expected, they may be more tender than usual. Give these features lots of space.
Strong winds have transported snow in the alpine. This is a photo of the North side of Magnum where many gullies are cross-loaded.
South of Turnagain – Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas and strong winds over the last few days have 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 slopes.
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: Strong Easterly winds diminished to light in the morning. Skies were overcast and light rain fell most of the day, but only a trace was recorded. Temperatures remained above freezing in the mid and lower elevations and rain/snow line may have reached 3000’+ in coastal areas of our zone. Partial clearing occurred overnight.
Today: This morning temperatures are expected to fall into the mid 20’s F in the Alpine as skies will continue to clear. Temperatures at sea level should dip below freezing by this evening. Wind will be light and variable. No precipitation is expected today.
Tomorrow: Clear skies should continue through Friday. Temperatures will remain in the 20’s F and winds are expected to remain light. The next chance for precipitation is Saturday into Sunday.
*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′)||35||0||.1||52|
|Summit Lake (1400′)||33||0||0||21|
|Alyeska Mid (1700′)||35||0||.02||40|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||32||*N/A||*N/A||*N/A|