Triggering a fresh wind slab avalanche will be our main concern. Ridgetop winds from the Northwest picked up yesterday and have strengthened overnight. Several wind slabs (mostly small, some large) were reported in the Turnagain Pass area along with one large natural seen in the Skookum Valley. These were around 1 foot thick and running far – due to entrainment of 4-8+” of loose snow sitting on hard old surfaces. The increase in wind overnight will only increase the size and likelihood of triggering these slabs. Although winds are forecast to decrease today, they could persist through the daylight hours. Unusual loading patterns have been seen with this wind direction and therefore all aspects are suspect. Wind slabs should be mostly found in the Alpine above the trees, but could also be found in open areas in the trees.
What to watch for:
– Recent avalanches – take a look around today, visibility should be good
– Shooting cracks from your snowmachine/skis/board
– Areas that are currently being wind loaded or that ‘look’ as they have been recently – round and pillowed surfaces
– Watch out from above – a party yesterday was washed over by a natural wind slab/sluff to their waist.
*Wind slabs are a surface instability that can typically be easily identified if we watch for them. Unlike the deeper weak layers mentioned below.
Sluffs: Sluffing in Friday’s storm snow (4-8+”) will be likely on steep slopes again today.
Solar effects: If the winds die down enough on South facing slopes, the sun will have a good chance at warming the surface creating moist sluffs and possibly triggering a fresh wind slab. In this case, avoid steep solar aspects if you notice roller balls or point releases under rocks.
Natural and skier triggered sluffs and wind slabs seen in the Magnum/Cornbiscuit (Subperbowl and Goldpan) area yesterday. (Photo: Mike Records)
Sluff on the North side of Magnum – seen from Sunburst ridge. (Photo: Allen Dahl)
Cracking in the new snow – sign of finding a wind slab. (Photo: Allen Dahl)
Triggering a slab avalanche breaking in persistent weak layers 1-3 feet deep remains possible above 1000’. Additionally, a wind slab or sluff has the potential to step down and trigger one of these layers. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in the upper elevations, and a layer of facets over a melt-freeze crust is suspect in the mid elevation band. Be suspect of the older snow under Friday’s storm snow. Red flags like shooting cracks or “whumpfing” may not be present before a slope releases. Evaluate the terrain for consequences and be aware of places that haven’t seen much traffic. These less traveled places are more suspect for triggering these deeper layers.
Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if the wrong spot is found above 3,000′. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass.
Mostly cloudy skies gave way to partly sunny skies late in the day yesterday. A trace to an inch of snow was recorded as Friday’s storm moved out in the morning. Ridgetop winds were moderate with strong gusts from the Northwest and have increased overnight. The Seattle Ridge station has been averaging 20-35mph with gusts to 60mph overnight. The Sunburst station on the other hand, is somewhat protected from this wind direction and reporting lower than observed winds (averages 10mph from the NW). Temperatures were in the teens at the upper elevations and 20’sF in valley bottoms.
For today, we can expect the ridgetop winds to remain moderate to strong from the Northwest, with averages between 10-20+mph and gusts to 50mph. Skies should be mostly sunny until later tonight when clouds move in along with snowfall. Overnight, we could see 2-3″ of new snow. Temperatures will be in the 5-15F range along the ridgelines and 15-25F in valley bottoms.
For Monday, the next system should be impacting the area. The Southwesterly flow associated with this storm will favor snowfall in the Hatcher Pass and Front Range zones more than Turnagain Pass where only 4-6″ of new snow is expected. See graphic from the NWS below. Strong Northwest winds are expected late Monday and into Tuesday as the system exits. Temperatures will remain cold enough for snow to sea level. Stay tuned!
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||27||0||0||68|
|Summit Lake (1400′)||19||1||0.1||30|
|Alyeska Mid (1700′)||19||1||0.05||60|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||18||NW||26||59|
|01/26/20||Turnagain||Observation: Pastoral||Allen Dahl|
|01/26/20||Turnagain||Observation: Tincan trees and north side Tincan Ridge||Joe Kurtak, Anchorage Nordic Ski Patrol|
|01/25/20||Turnagain||Observation: Magnum||Ryan Van Luit Forecaster|
|01/25/20||Turnagain||Observation: Tincan||Eric Roberts/ Kakiko|
|01/25/20||Turnagain||Avalanche: Sunny Side of Seattle||Peter Wadsworth|
|01/23/20||Turnagain||Observation: TIncan||Eric Roberts|
|01/23/20||Turnagain||Observation: Goldpan||Allen Dahl|
|01/22/20||Turnagain||Observation: Sunburst||Adrian Beebee|
|01/22/20||Turnagain||Observation: Sunburst||Ryan Van Luit Forecaster|
|01/22/20||Turnagain||Observation: Seattle Ridge||W Wagner Forecaster|
Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: firstname.lastname@example.org
|Area||Status||Weather & Riding Conditions|
This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.