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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, April 5th 2018 5:31 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects and elevations, but may increase to HIGH by early evening. Triggering a fresh storm slab 1-3’ thick is likely on slopes steeper than 35 degrees. Natural wet-loose avalanches are possible in the afternoon with daytime warming and may become more likely on Southerly aspects if the sun comes out today. If you see natural avalanche activity this is a sign the danger is increasing and it will be important to avoid all avalanche terrain including runout zones. In addition, keep in mind there is still a chance for triggering a deeper avalanche 3-4+’ thick in older layers of the snowpack. 


 Show the Complete North American Avalanche Danger Scale
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.
Special Announcement

Dangerous avalanche conditions are expected near Seward, Moose Pass and Cooper Landing due to 1-2 feet of new snow. If you're headed to Lost Lake, Snug Harbor or Carter Lake avoid being on or under any steep slopes today. Sun and daytime warming could increase the potential for natural avalanche activity later in the day. 

SKOOKUM VALLEY drainage remains closed to snowmachines for the remainder of the season as per the Chugach National Forest Plan.  Please stay to the West of the railroad tracks until you are South of Leubner Lake.

 


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

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Size

A storm moved through our region yesterday bringing strong Easterly winds and dumping 1-2 feet of new snow across our region. Girdwood was favored with Alyeska reporting 18” at midway and 24” at the top. On the Northside of Turnagain Pass totals were estimated in the 12”-18” and observers reported around 8-10” by 6pm last night at Sunburst. Don’t forget these storm slabs were formed by strong Easterly winds and slabs could be 2-3 feet thick on leeward features in the alpine, especially in Girdwood Valley. This new snow fell on variable surfaces including a slick melt/freeze crust on Southerly aspects and patches of loose faceted snow and crusts on other aspects.  Either way bonding will be poor and triggering a storm slab is likely today. The size of the slab will depend on the size of the terrain. An observer at Tincan reported lots of human triggered storm slabs and loose snow sluffing in the trees throughout the day. Careful snowpack evaluation and caution route finding will be essential. Warming in the afternoon may increase the likelihood for triggering storm slabs. If you see any natural avalanche activity this is a sign to avoid all avalanche terrain and stick to flat mellow terrain well away from the runout zones of larger slopes. 

  • Turnagain Pass: 10-18”  (~1.0” SWE)
  • Summit Lake: 4-6” (0.3” SWE)
  • Girdwood -Alyeska midway: 18” (1.4” SWE) 
  • Portage - Bear Valley: 14” (1.3” SWE)

Turnagian Pass Snowstake at the DOT RWIS weather station reported around ~15" of new snow yesterday.

 

Observers yesterday on Sunburst reported 9" of new snow by 6pm. This was quite a bit less than observations from Tincan. 


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

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Size

SPRINGTIME WARMING: Daytime temperatures are expected to increase to the mid 30F’s near ridgetops and low 40F’s near sea level as snow and wind taper off in the afternoon. If the sun appears today or any radiation through cloud cover - this will increase the potential for natural wet-loose avalanches later in the day. Southern aspects will be more likely if the sun come out, but all aspects are suspect if clouds trap the heat. Lower elevations such as Placer Valley and Portage may see more natural activity on lower elevations slopes, especially in channeled terrain. Pay attention to how the snow changes throughout the day. Heavy moist snow and rollerballs will be your first clue the snow is changing. Any natural avalanche activity will be an obvious sign the snowpack is becoming more dangerous and it will be important to adjust your plans. Although it's not expected, there is potential for a storm related avalanche to trigger a deeper more dangerous avalanche. More on this below.

 


Additional Concern

Deep Persistent Slabs

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. Little is known about how the snowpack is adjusting to its new load, and if one of these older weak layers, facets and buried surface hoar, could wake up today.  This is an additional reason to avoid being on or under any larger slopes. Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges. 

This is a snowpit from yesterday on Sunburst and shows the weak interface between the new snow and old snow as well as several older weak layer buried a few feet below. 


Mountain Weather

Yesterday 1-2 feet of new snow fell across our region and strong Easterly ridgetop winds averaged around 25mph with gusts in the mid 40’s mph. Temperatures at 3000’ remained 20F and temperatures at 1000’ bumped in the low 30F’s mid day, but all precipitation remained snow to sea level. The heaviest snow fell yesterday afternoon and early evening becoming light overnight. 

Today skies will be overcast in the morning becoming mostly cloudy later in the day and partly cloudy by this evening. Precipitation is expected to taper off this morning. Easterly winds will be 15-25mph this morning and decrease this afternoon becoming light and variable by early evening. Daytime temperatures may reach the mid 30F’s near ridgetops and low 40F’s at sea level. Overnight temperatures are expected to drop into the low to mid 20F’s. 

Scattered snow showers are possible on Friday, but not much accumulation is expected. Daytime highs will be in the upper 30F’s and overnight lows to drop in the 20F’s. Winds will be light and variable. Saturday could be our warmest day this spring with highs in the 40F’s and partly cloudy skies. 

*Center Ridge Snotel reported 0.4" SWE and has been under reporting SWE last few storms. Was estimated Snow Water Equivalent (SWE) to be around 1.0" based on the hieght of new snow of 12".  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28  12  *1.0  85 
Summit Lake (1400') 27  .3  37 
Alyeska Mid (1700') 28  18  1.35  84 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  ENE  24  48 
Seattle Ridge(2400') 23  ESE  17  39 

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
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