Sunday, December 17th 2017 5:32 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
The avalanche danger is CONSIDERABLE in the Alpine elevation for triggering a 2-4'+ slab avalanche breaking near the ground. The danger is more pronounced in regions of the forecast zone that did not receive significant snow during the past 2 weeks, such as areas on the South end of Turnagain Pass. Careful snowpack evaluation and conservative decision-making is essential while we gather more information. In addition, there is a MODERATE avalanche danger at all elevations above 1,000' where triggering a lingering 1-2' thick wind slab or storm slab is possible. Cornice falls are also possible for those traveling along ridgelines. There is no hazard below 1,000' due to lack of snow.
|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.|
Mark your calendars!! Two upcoming CNFAIC Fireside chats, December 19th at Blue & Gold Boardshop in Anchorage and December 21st at Powder Hound Ski Shop in Girdwood. Both will discuss lessons learned from past avalanche incidents. We hope to see you there!
After two weeks of rain and warm temperatures, a welcome cooler storm arrived Friday bringing 12 - 20" of new snow across the region. The wet snowpack below 2,500-3,000' is slowly freezing as it's now capped by this new snow. No avalanche activity was seen or heard of yesterday, including any small avalanches relegated to the new snow. However, very few people have been in the mountains, save for the most popular areas.
Our main concern are deep persistent slab avalanches at the higher elevations in thin snowpack areas. This means avalanches breaking deep in the pack above 2,500', and in our case in a weak layer of facets near the ground. We are uncertain as to the extent and likelihood of triggering a large slab, but until we gather more information we recommend following the travel advice for CONSIDERABLE avalanche danger, which includes careful snowpack evaluation and conservative decision-making. Snow pit results at 3,300' on Tincan yesterday pointed to good stability and this is a good sign, but remember this is one pit in a place that received significant snow compressing the weak layers. Areas on the Southern end of the pass and extending toward Summit Lake received less snow and are suspect for harboring reactive facets near the ground. A thinner snowpack also means triggering is more likely.
Keep in mind that no Red Flags are likely to be seen with this avalanche problem. In order to assess the weak layer in a snow pit you must dig to the ground. This makes it more difficult to know how touchy this problem is. Any help from you is much appreciated! Please let us know if you hear any whumpfing or collapsing, if you dig to the ground let us know what you find. Last, mid-elevations, roughly below 2,500' and even up to 3,000' in places, saw enough rain that the pack is now freezing into thick crusts, limiting avalanche activity.
The snowpack is still thin in area South of Turnagain Pass, pictured below is the Seattle Creek headwall and Big Chief on the right. (photo Sam Galoob)
Anywhere from 12 - 20" of new light snow from Friday's storm sits on either a moist crust or dense snow. We found good bonding with the new and old snow interface yesterday. What we did find were stubborn wind slabs and storm slab potential as the storm snow had yet to completely bond. Today, watch for lingering wind slabs and areas where the storm snow feels stiffer over lighter. Quick hand pits and using your pole to cut small blocks are great ways to assess these 'surface instabilities' along your route. Look for blocks you cut to easily slide off and watch for cracks that shoot out from you. There is plenty low density snow that a little bit of wind and/or warming could form a slab.
New snow from Dec 16th showing signs of bonding and stabilizing.
Yesterday saw overcast skies with a few sunny holes poking through. There was no precipitation recorded during the past 24-hours, except for a trace in the Girdwood Valley late morning. Winds were light from the East with moderate gusts. Temperatures were mid 30'sF at sea level, 30F at 1,000' and mid 20'sF along ridgetops.
Today, partly cloudy skies and cooler temperatures are expected with no precipitation. Ridgetop winds are forecast to shift Northerly today and remain light 5-10mph with stronger gusts. Temperatures are cooler in valleys this morning, 15-20F, as an inversion has set in while ridgetops are in the low to mid 20'sF. Expect valley temperatures to climb during the day and ridgetops continue cooling with cold air moving in from the North.
Monday, skies are forecast to finally clear and a sunny day is on tap, again with cooler temperatures and light winds. Tuesday another system heads in. This one looks to bring around 4-8" of snow with the rain/snow ~1,000'. Stay tuned!
* Sunburst weather station is down due to loss of battery power.
PRECIPITATION 24-hour data (6am - 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880')||27||0||0||33|
|Summit Lake (1400')||21||0||0||11|
|Alyeska Mid (1700')||28||trace||0.03||29|
RIDGETOP 24-hour data (6am - 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
Snowpack at the Motorized Parking Lot: 18" totoal: bottom 8" is wet snow beginning to freeze, top 10" is new snow from Dec 15.
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: Jan 13, 2019 )
|AREA||STATUS||WEATHER AND RIDING CONDITIONS|
|Twentymile:||Closed||Closed. Forest Service is monitoring conditions.|
|Lost Lake Trail:||Open||Please stay on trail to avoid resource damage through forested areas.|
|Primrose Trail:||Open||Please stay on trail to avoid resource damage through forested areas.|
|Resurrection Pass Trail:||Closed||Closed for the 2018/19 season. Next season will be open to motorized use.|
|South Fork Snow River Corridor:||Open|
SNOW AND AVALANCHE HOTLINE (907) 754-2369
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