Once again, our primary concern deals with deep slab avalanches. These are failing in the weak layers at the bottom of the snowpack and can bring down large, dangerous and far running slides. It has been 4 days since the last deep slab was triggered but today the likelihood will go up with the rapid rise in temperature and the addition of rain and/or wet snow.
The precipitation amounts for this storm are not exceptional for this year around Turnagain Pass but the warm temperatures are. Most of our start zones lie in the 2,000 – 4,000’ elevation band and it is exactly this band which has harbored colder, dry snow so far this year and will get a shock as it warms up today. The slab that overlies our weak October and November snow is essentially one cohesive layer 4-8′ thick. It is a complex phenomenon as to why rapid warming destabilizes a dry snowpack. Essentially, the properties of the slab (our 4-8′ cohesive layer) change which increases the stress on the underlying weak layers (our October and November facets). There is a good chance that there are several slopes out there teetering on the balance and that balance may be tipped today.
Rain on snow near 3000ft and below will give our mid-elevation snowpack a jolt and decrease stability rapidly. Though the lower elevations (below 1,000ft) have seen their fair share of rain it is the next 2,000ft above this that is the biggest problem. As many old-timers say “rain on dry snow is never a good thing”. These wet avalanches can initiate in the top foot or two of the pack where the rain is being absorbed and become quite large on their descent by entraining additional snow in its path. They also have the ability to “step down” and trigger a deep slab avalanche, in which case will mostly likely be quite large. Wet snow avalanches contain very dense snow that is typically slow moving but they also mow down and destroy most things in their path.
Very warm air is on our doorstep as tropical moisture is being pulled up into our neck of the woods. Anchorage is already in the thick of it but Turnagain Pass is trailing a bit behind. We should see temperatures steadily climb throughout the day and top out near 32F at 4,000′ by this afternoon. The rain/snow line is currently around 1,500′ but will rise to around 3,000′. There has been 0.9 € of water equivalent (7 € of high density snow) in the past 24 hours as of 6am on Turnagain Pass and quite a bit more, 2-2.5 € of water equivalent (~18 € heavy snow), in the Girdwood Valley. Ridgetop winds are out of the SE averaging 25mph and gusting up to 50mph.
We should see around another 1 € of water through the day with most of it falling as rain and very wet snow near 3,000′. Wind will remain SE and in the 20-30mph range with higher gusts on the ridges. Temperatures at treeline will rise to the upper 30’s. F. The rain and wet snow will continue overnight and taper off tomorrow with cooling temperatures.
Pictured below – the “fire hose” of tropical moisture pointed right at southern AK. (current on page refresh of GOES IR image)
Fitz will issue the next advisory tomorrow morning, January 14th.
|04/19/21||Turnagain||Avalanche: Triangle, Seattle creek||Will Morrison|
|04/18/21||Turnagain||Avalanche: Turnagain Pass Road Obs||Andy Moderow|
|04/18/21||Turnagain||Observation: Seattle Ridge, approximately 300 yards south of the up track||Brent Byrne|
|04/17/21||Turnagain||Avalanche: Road obs||Johnston-Bloom / Moderow Forecaster|
|04/16/21||Turnagain||Avalanche: Seattle Ridge||Wendy Wagner Forecaster|
|04/16/21||Turnagain||Avalanche: Turnagain Pass, non-motorized side seen from Seattle Ridge||CNFAIC Staff Forecaster|
|04/16/21||Turnagain||Observation: Sunburst||Lance breeding|
|04/15/21||Turnagain||Observation: Tincan||Schauer/ Rothman Forecaster|
|04/13/21||Turnagain||Observation: Turnagain Pass Road Obs||A Schauer Forecaster|
|04/12/21||Turnagain||Observation: Tincan||Johnston-Bloom / Latosuo 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.