Tuesday, December 16th 2014 6:23 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
A HIGH avalanche danger continues in the backcountry at elevations above 2,500'. Storm snow slab avalanches 2-5' in depth have the potential to release naturally and human triggered avalanches are very likely. These have the potential to run into the treeline elevation band between 1,000' and 2,500' where a CONSIDERABLE avalanche danger exists. Additionally, wet avalanches are possible at the mid-elevations on steep slopes over 40 degrees. Travel in avalanche terrain (slopes over 35 degrees with nothing steeper above you) is not recommended.
It is game on in the backcountry. Although there is no snow at the road elevations, there is plenty of snow at the higher elevations. This week marks the first time this season we have a documented persistent weak layer in the snowpack. When this storm cycle finishes, skies clear and folks start getting out - have your hackles up! This set up, described below, has lead to accidents in the past and we need to be patient, let the new snow settle and prove itself NOT guilty before getting on slopes over 35 degrees.
The next advisory will be Thursday Dec18th at 7am.
Avalanche Outlook for Wednesday: With decreasing temperatures and precipitation, the avalanche danger is expected to drop to CONSIDERABLE at elevations above 2,500' and to MODERATE below 2,500'. A decline in natural avalanche activity is expected, however human triggered large avalanches 2-5' deep will remain likely above 2,500'.
|Show the Complete North American Avalanche Danger Scale|
|Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.|
|Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.|
The Alaska Avalanche School will be hosting a backcountry weather course, Weather for the Backcountry Traveler, this Wednesday evening. Taught by longtime avalanche professional and Alaska Avalanche School Instructor Eeva Latosuo. This is a great way learn and/or sharpen your weather skills!!
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.
PRECIPITATION 24-hour data (6am - 6am)
|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|
RIDGETOP 24-hour data (6am - 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
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).
Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.
(Updated: Apr 20, 2018 )
|AREA||STATUS||WEATHER AND RIDING CONDITIONS|
|Johnson Pass:||Closed||Closed as of April 20|
|Placer River:||Closed||Closed as of April 17th|
|Skookum Drainage:||Closed||Closed as of April 1st.|
|Twentymile:||Closed||Closed as of April 13th|
|Lost Lake Trail:||Closed||Closed as of April 13th|
|Primrose Trail:||Closed||Closed as of April 13th|
|Resurrection Pass Trail:||Closed||Closed as of April 20th|
|South Fork Snow River Corridor:||Closed||Closed as of April 13th|
|Summit Lake:||Closed||Closed as of April 20th|
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