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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, January 2nd 2018 4:25 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger remains HIGH above 1000' due to rain, heavy wet snowfall and strong winds.  Natural avalanches are likely and human triggered avalanches are very likely today. As the new snow, rain and wind overloads a weak layer of buried surface hoar and facets, avalanches are becoming larger and more dangerous. Travel in avalanche terrain is NOT recommended. This includes areas that are in the runout from avalanche paths above. 

The avalanche danger is CONSIDERABLE below 1,000’ where debris from avalanches above may run.


 Show the Complete North American Avalanche Danger Scale
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

Dangerous avalanche conditions are expected in the Southern Kenai Mountains (such as, Seward and Lost Lake) due to heavy snowfall.

Join CNFAIC on Wednesday, January 3rd from 7pm - 8:30 pm at the Blue & Gold Boardshop for a discussion on Understanding Weak Layers and the Current Snowpack at Turnagain Pass. 


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

This series of storms continues to build storm slabs and overload the weak layer of surface hoar and near surface facets that formed last week. Yesterday folks continued to trigger small avalanches in the Tincan Trees and observed signs of instability including whumpfing, cracking and hand pits failing on isolation. There was low visibility which made it difficult to see into the alpine but strong winds were rapidly loading leeward slopes. Sunburst saw gusts as high as 102 mph. Temperatures rose and the snow became more and more upside down. Since the storms started on Saturday, Center Ridge Snotel has received 1.8" of water and mid-elevation stations in Girdwood received 2.4" of water.  This translates to 15-30" of total snow since Saturday up high. Unfortunately at lower elevations some of this precipitation came as rain overnight as temperatures rose and rain fell to as high as 2300'. Today the recipe for avalanches is pretty simple. Weak snow has been overloaded by heavy snow, wind loading or rain. Slabs in upper elevation terrain could be 2-4 feet thick.  Travel in avalanche terrain (on slopes steeper than 30 degrees) is not recommended. Runout zones should also be avoided due to the potential for natural avalanches and as always steer clear of terrain traps. Even a small avalanche in the wrong spot could be very hazardous. 

Screen shot of Sunburst Weather Station this am. Note the wind profile since Saturday = rapid loading!

Layer of surface hoar that is buried below the storm snow. This is the weak layer of concern. 

Slopes triggered by skiers and boarders on Sunday were reloaded on Monday. 

 


Avalanche Problem 2

Wet Slab

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Rain fell overnight to as high as 2300'. It is adding weight to the already stressed snowpack and breaking bonds between snow grains. Water saturating new snow could cause natural wet loose or wet slab avalanches. Triggering wet avalanches in the treeline elevation band is also likely today in steep terrain. This is another reason travel in avalanche terrain is not recommended today. 


Additional Concern

Deep Persistent Slabs

In the alpine, above 3,000’, rapidly loading slopes may awaken a large and dangerous deep slab avalanche. At these elevations, a hard slab, 3-5+ feet thick, is sitting on top of weak sugary snow (basal facets) near the ground. As new snow increases the load over this snowpack structure during the current storms, there will be the potential for large natural avalanches. Between storms, human triggered deep slab avalanches will be possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as breaks between storms may allow for travel to the Alpine. 

 


Mountain Weather

Yesterday there were light rain and snow showers in the morning and the next storm system picked up mid-day with low visibility, gusty winds, and heavier snowfall and rain.  Approximately 10-15" of additional new snow fell in the upper elevations of Girdwood Valley and the Turnagain Pass area. 24-hour totals are below in the table. Lesser snow amounts were seen on the South end of Turnagain Pass and in the Summit Lake area. Ridgetop winds were Easterly averaging 35-45mph with gusts to 102mph. Temperatures were in the mid 20Fs at treeline and rose to mid 30Fs at 1,000'. Overnight rain fell to as high as 2300'.

Today, rain and snow showers continue with another 5-10" of snow or .35 inches of rain possible.  Rain/snow line is forecasted to be around 2300' today. Precipitation will taper off overnight. Temperatures start warm today in the upper 30Fs above 1000' and 40Fs at sea level.  They will cool down this evening into the 20Fs. This will bring the rain/snow line down, with snow showers possible overnight.  Winds will be easterly 20-30 mph, gusting into the 50s. Winds speeds will decrease in the afternoon.

Wednesday into Friday looks to be a break in the storms with a chance of some sunshine, lighter winds and temperatures in the 20s. Stay tuned for the next storm details, as there is still a fair bit of uncertainty about what the weekend will bring.

*Seattle Ridge is anemometer is rimed and under reporting.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 34   9 .8   48
Summit Lake (1400') 33 1 .2   14
Alyeska Mid (1700') 32  6  1.35  41

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  23  ENE 42  102 
Seattle Ridge(2400')  28  *n/a *n/a  *n/a 

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

Subscribe to the Turnagain Area Avalanche Advisory:

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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