Saturday, December 23rd 2017 4:48 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
The avalanche danger is CONSIDERABLE in the Alpine where triggering a wind slab 1-2’ thick is likely on steep leeward features where strong winds have been actively transporting snow. In the high elevations slopes (above 3,000') winds have been adding stress to a more dangerous deep slab problem that could release near the ground. Obvious clues like ‘whumpfing’ and shooting cracks may not be present until its too late. Careful snowpack evaluation and cautious route-finding are essential today.
The avalanche danger below 2500' is MODERATE for wind slab avalanches around a foot thick. At these lower elevations, watch for wind loaded slopes where triggering a shallow wind slab is possible. There is no hazard below 1,000' due to lack of snow.
**Click HERE for the Summit Lake Summary
|Show the Complete North American Avalanche Danger Scale|
|Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.|
|Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.|
Large plumes of blowing snow were present yesterday along all the tallest peaks around our region and strong Easterly winds are expected to continue today. Wind loaded snow could be on all aspects due to top loading and cross loading. These slabs will be hard and supportable and have the classic smooth pillow shaped look. Wind slabs could easily be located further down slope than expected and have the potential to fracture above you. Triggering even a small wind slab could have very high consequences especially in the upper elevations where there is also a potential for initiating a much larger and more dangerous deep slab avalanche. More on this below. Should you go into the upper elevations maintain a conservative mind-set and avoid big objective slopes including their runout zones.
Active wind loading as seen yestereday on Big Chief in the Seattle Creek area.
Variable surfaces are preseent throughout the alpine. Note the crossloading pattern including the pillowed shaped snow loaded along gullies on the SE aspect of Seattle Ridge
On December 20th, two skiers were approaching Pastoral and remotely triggered a very large avalanche from below. Luckily they were able to run from its path and avoid being caught. This is a very scary set-up that is likely not going away soon. Deep slabs are located in the upper elevations of our forecast zone, above 3000’, on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facets. Observations over the last few weeks indicate this poor structure set-up is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart. Keep in mind:
- Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks
- Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
- Thicker areas (3-5+’ thick) will be difficult trigger and several tracks may be on a slope before someone finds a trigger point
- It is possible to trigger this avalanche from below and it could run further than expected
- Large snow covered slopes that do not have piles of old debris under them are all suspect
Photo taken on Dec.21, the day after the Pastoral avalanche. Approximate route of where the party triggered this avalanche and retreated out of its way.
Photo taken on Dec.21st when strong winds started impacting our region. Note theNorthern Chutes on lookers left side have not avalanche yet and are actively loading snow.
Yesterday skis were partly cloudy with strong Easterly winds averaging in the mid 20’s with gusts in the 60’s. Warm air was observed at lower elevations mid to low 30F’s and temps in the mid 20F’s along ridgetops. No precipitation was recorded.
Today expect skies to be mostly sunny with Easterly winds elevated averaging in the 20’s with gusts in the 40’s. Day time temps at 1000’ are expected to be in the mid to low 30F’s and dip down to mid 20F’s overnight. High clouds are expected to move into our region tonight with a few flakes possible overnight.
Scattered snow showers are possible tomorrow, but little to no accumulation is expected. Temperatures are expected to range from 20F-30F. Winds should decrease tomorrow morning and remain Light from the East.
PRECIPITATION 24-hour data (6am - 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880')||31||0||0||31|
|Summit Lake (1400')||25||0||0||11|
|Alyeska Mid (1700')||32||0||0||26|
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: May 06, 2018 )
|AREA||STATUS||WEATHER AND RIDING CONDITIONS|
|Johnson Pass:||Closed||Closed as of April 20th|
|Placer River:||Closed||Closed as of April 17th|
|Skookum Drainage:||Closed||Closed as of April 1st.|
|Turnagain Pass:||Closed||Closed as of May 7th. Happy summer, see ya when the snow flies!|
|Twentymile:||Closed||Closed as of April 13th|
|Carter Lake:||Closed||Closed as of 4/27|
|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|
|Snug Harbor:||Closed||Closed as of 4/27|
|South Fork Snow River Corridor:||Closed||Closed as of April 13th|
|Summit Lake:||Closed||Closed as of April 20th|
SNOW AND AVALANCHE HOTLINE (907) 754-2369
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