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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Monday, March 20th 2017
Created: Mar 20th 4:18 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects and elevations today. 1-3' of new snow sits on weak snow. Triggering a slab avalanche and/or loose snow avalanche is likely on slopes 35 degrees and steeper. Warming afternoon temperatures and a chance of sunny skies will make natural avalanches possible. Cautious route finding and conservative decision-making are essential. Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth. 

Summit Lake: Read the Saturday Summit Summary HERE.

 


Primary Concern

The forecasted scattered snow showers turned into a full-blown storm and 7-24 inches of snow fell across the advisory area in the past day and a half. Turnagain Pass received a foot. Girdwood Valley 7-10", Portage Valley 18" and Skookum/Placer was the winner with up to 24". The new snow fell on weak surface snow that formed during the 3 weeks of high pressure (near surface facets and surface hoar). Yesterday observers reported natural loose snow avalanches and small slabs. Today as the snow settles and the slab sets up triggering a larger storm slab avalanche will be likely on steep slopes from sea level to the Alpine.  Along ridgelines NE winds have stiffened snow and wind slabs will be likely in leeward terrain. Warming temperatures this afternoon and the possibility of clearing skies and sun will add to the likelihood of triggering and may cause natural avalanches. Whumpfing and shooting cracks were observed yesterday, both are obvious clues that the snowpack is unstable. Be on the lookout for these signs today.  

New snow in Skookum over old faceted snow. Photo: Conrad Chapman

Cracking in the new snow. Photo: Conrad Chapman

 


Secondary Concern

Yesterday numerous natural loose snow avalanche (point releases) were observed as new snow accumulated over weak surface snow and skiers triggered sluffs in steep terrain.  Natural damp or wet loose snow avalanches will be possible today with warming afternoon temperatures and sun. Triggering a loose snow avalanche will remain likely throughout the day. These avalanches could also initiate a slab on the slope below as the slab become more cohesive today. Remember loose snow avalanches/sluffs/point releases can be very hazardous if they knock you off your feet and/or push you into a terrain trap or slide onto you in a terrain trap from above. 

 

Dry loose avalanches on West face of Magnum. Photo: Conrad Chapman


Additional Concern

Persistent Slabs and Deep Slabs: In addition to the now buried weak surface snow (near surface facets and surface hoar) there are a variety weak layers in our thin snowpack. The February 9th buried surface hoar sits 2-4+' below the surface and faceted snow sits in the mid and base of the pack. Due to the lack of changing weather over the past three weeks, these weak layers (with varying degrees of strength) have been in a ‘dormant stage’.  Although unlikely today, an avalanche breaking deeper in the pack isn't completely out of the question especially in areas such as Johnson Pass, Lynx Creek and on the Northern side of Girdwood Valley (near Crow Pass). Observers continue to find poor structure. The buried weak layers will require monitoring as the load on top increases incrementally and as temperatures rise. Yesterday was the warmest temperatures we have seen in the last month. An avalanche triggered in the upper snowpack could trigger a deeper avalanche. 

Snow pit in Spokane Creek on March 18th. An Extended Column Test showed propagation potential on the Feb. 9th buried surface hoar layer. Photo: Chris McNeil


Mountain Weather

Yesterday was mostly cloudy in the morning with snow falling until around 1pm. Snowfall was heavy at times. As noted above storm totals ranged from 7-24". Skies became partly cloudy in the afternoon and temperatures rose. A few low to mid elevation weather stations hit just above 32F. The temperatures in the Alpine stayed in the teens to low 20Fs. Winds were predominately NE 10-20 mph gusting into the 30s. Overnight another couple of inches fell and skies were partly to mostly cloudy.

Today there is a chance of snow showers throughout the day with potential clearing this afternoon. Skies will be mostly to partly cloudy. Winds will be light and easterly. Temperatures will be in the 20Fs to 30Fs with the high forecasted to be above freezing. 

Overnight there is a chance of showers and tomorrow is forecasted to be clear and sunny with highs in the 20Fs. Sunshine and mostly clear skies look to be the dominant pattern for most of the week. 

PRECIPITATION 24-hour data (6am - 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  25  10  .2 69 
Summit Lake (1400')  21  2  .2  30
Alyeska Mid (1700')  22  6  .4 66 

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  14 NE  12  33 
Seattle Ridge(2400')  18 ESE-ENE   8  21

8

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).

Winter snowmachine use open/closed status and riding conditions updates

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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