As of this morning, the storm rages on. Although it is raining below 1,500′, it is snowing and blowing at the upper elevations. Storm totals in these upper elevation areas have been variable: from only a few inches in the Summit Lake area to ~2′ on Turnagain Pass and 4′ or more in the Girdwood and Portage Valleys. These numbers are for ~3,000′ and above and are estimated from the amount of rain/wet snow reported from weather stations at lower elevations (see those water numbers in the Mountain Weather section). Along with the snow, ridgetop winds have been strong and sustained from the East. Considering this, slab depths for avalanche activity are variable, 2-5′ or more.
The primary concern for today and into the remaining part of the week will be how the new snow is bonding with the pre-existing surface. We have been talking a lot about a widespread layer of surface hoar that extended to the ridgetops before being buried under the current storm snow. This set up has the potential for inducing widespread avalanche activity. See video from yesterday. Unfortunately, with little to no visibility there is a good deal of uncertainty as to how the new snow has been acting. Along with this, our field days since the storm began have only allowed us to see what is going on from mid-mountain elevations and below.
All that said, the message is simple: Several feet of new snow combined with wind falling on a weak layer with a slick bed surface below requires a conservative mind set.
Below is the snowpack from a slightly scoured area on the Sunburst ridge yesterday. At 2,700′ the snow changed character significantly from wet to dry and the avalanche potential increased rapidly. This points to increasing danger with elevation. The nature of this weak layer can allow for wide propagation and triggering avalanches remotely, including from below.
Although it has been raining from ~1,700′ and below with wet snow falling up to ~2,500′, we have seen little wet avalanche activity. The rain has wiped out the snow cover below 1,500′, but in the elevation band from 1,500-2,500′ the snowpack goes from 0-2′. The main concern for wet avalanches is the new heavy snow (10-12″) sliding on the old hard surface underneath. I was able to trigger a push-a-lanche yesterday on a slope ~40deg. Avoiding steep slopes at these wet snow elevations, including runout zones from steep slopes above you, is recommended as this wet storm continues.
As we go into Wednesday, temperatures are forecast to cool. If this is the case, the mid-elevations will begin to freeze and wet avalanche potential will decline.
Beginning Saturday afternoon, we have seen several fronts and embedded low pressure systems move through the Eastern Turnagain Arm zone. Precipitation totals from the start of this event are below with the past 24 hour data in the tables. During this cycle the rain/snow line has fluctuated between 1,500′ and 2,500′ (higher in some locations). Easterly ridgetop winds have remained strong, averaging 25-40mph.
Storm totals in water equivalent (Saturday afternoon – Tuesday morning):
Turnagain Pass: 2-2.5″ H20
Girdwood Valley: ~4″ H20
Summit: Only ~.5″ H20
For later today, the storm looks to begin to cool off and slow down. We should see another .5″ of precipitation, 4-6″ of snow above 1,500′ (possibly more). Ridgetop winds will remain strong in the 20-30mph range from the East. Temperatures at 1,000′ look to fall from ~35F to 30F, with a rain/snow line decreasing to ~1,000′.
For Wednesday, continued light precipitation with falling temperatures is forecast. Models are showing ~.5″ of precip this evening through Wednesday evening with a rain/snow line dropping to 500′. Thursday we may see clearing skies before another warm system looks to move in.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||33||5+||1.2||30|
|Summit Lake (1400′)||34||0||0.3||4|
|Alyeska Mid (1700′)||35||0.5||2||14|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||29||N/A||N/A||N/A|
|04/21/21||Turnagain||Observation: Sunburst||Schauer/ Behney Forecaster|
|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|
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.