In the alpine a thicker snowpack exists and with it more uncertainty. Observers yesterday found depths to be in the 3-5’ range near 3000’. Two pit locations above 3000’ (on Tincan & Sunburst) found a layer of surface hoar buried 2-3’ below the surface. One party on Sunburst felt a collapse ‘whumpf’ around 2800’ along the West ridge and several large piles of debris were noted on steep Northern terrain from avalanches earlier in the week.
What does this all mean?
Triggering a large persistent slab is possible in steep terrain and will be more likely in thinner areas of the snowpack. It remains unknown how widespread this layer is across our region or how much avalanche activity occurred on it early in the storm that may be hidden. It may be more likely to trigger a persistent slab in places that received less overall precipitation like the Southern end of Turnagain Pass and Summit Lake. Persistent weak layers are tricky and hard to manage. Evaluate your consequences and choose conservative terrain. Be on the lookout for any obvious signs on instability like whumpfing, shooting cracks or any new avalanche activity.
Several snowpits dug in the upper elevations yesterday found buried surface hoar
Rollerballs and a small mid storm avalanche were visible yesterday. This visual is a little deceiving. Loose snow is covering a thin crust, but gradually disappears around 2700′.
A strong crust has formed below 2500’ but the snowpack remains very thin to nonexistent below 1500′.
Easterly winds are expected to increase to Moderate (15-25mph) late afternoon and into the evening. In the alpine there is snow available for transport and triggering a shallow wind slab on leeward features may be possible. Pay close attention to changing weather and be on the lookout for shooting cracks and drifting snow.
Yesterday: Temperatures remained below freezing with ridgetops near 15F most of the day and mid 20F’s near 1000′. Winds were light and variable. No measureable amount of precipitation fell. Skies were broken in the morning becoming overcast in the afternoon.
Today: Winds are expected to be light and variable in the morning shifting to an Easterly pattern and increasing to Moderate (15-30mph) by tonight. Temperatures are expected to remain below freezing in the mid and upper elevations for today. Scattered snow showers are possible in the upper elevations and skies will be overcast.
Tomorrow: Saturday temperatures are expected to rise as a second front moves up Cook Inlet. Rain/snowline may push as high as 1500′ by late morning. A few inches of snow is possible above this elevation and rain showers at lower elevations. Easterly ridgetop winds will remain Moderate (15-25mph) through Saturday evening.
*Seattle Ridge weather station stopped collecting wind data at 10 pm on Nov 27, 2018. *Center Ridge weather station depth sensor showed 2″ increase, but no actual accumulation occurred.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||24||0||0||*10|
|Summit Lake (1400′)||19||0||0||0|
|Alyeska Mid (1700′)||25||0||0||*N/A|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||21||*N/A||*N/A||*N/A|