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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Sunday, April 23rd 2017
Created: Apr 23rd 6:28 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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
 Show the Complete North American Avalanche Danger Scale
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Special Announcement
  • This coming week is the last week the CNFAIC will issue avalanche forecasts. These will be today, Tuesday, Thursday and Saturday mornings. We will be closing up shop on April 30th.

  • Observations: We will continue to monitor and post observations all spring and summer - so please keep us, and the community, posted on any snow/avalanche information you may come across on your upcoming adventures!!
  • We have stopped issuing our Saturday Summit Summary for the 2016/17 season. Click HERE for our Springtime Avalanche tips.

The Bottom Line

The avalanche danger is expected to rise to CONSIDERABLE late in the day on Sunday and into Monday. Warm temperatures continue to soften the snowpack creating a wet avalanche hazard on all slopes over 35 degrees in steepness. Natural wet avalanches may begin to release as early as this afternoon and are expected to occur on Monday. Steep and rocky slopes with a shallow snowpack are the most suspect for releasing. Human triggered wet slab and wet loose avalanches will be likely on steep slopes that have a wet, saturated and unsupportable snowpack.

Hiking on summer trails during the springtime warm-up (including the Byron Glacier trail, Crow Pass, etc).  Extra caution is advised for trails that cross under avalanche paths. Avalanches possible at the higher elevations could send debris over snow-free hiking trails. 
 

MONDAY APRIL 24th AVALANCHE OUTLOOK:
A CONSIDERABLE avalanche danger is expected for Monday. Increased warm weather conditions will enhance the possibility for natural wet avalanches on all aspects above 1,000'. Please see the discussion below for more details.


Primary Concern

During the springtime warm-up and the snowpack melt-down (or shed cycle), there is an 'old-timer' rule of thumb. This goes as follows: One can start expecting wet avalanches to begin after three consecutive nights with no re-freeze along the ridgetops. Last night was the second night without a sold re-freeze, and tonight will be the third..... 

Although many South and Southeast slopes such as Seattle Ridge have already melted down over the past 2 weeks of sunny weather (meaning significant wet avalanche activity has occurred), there are still West, North and East slopes that remain intact. Westerly and Easterly slopes are theoretically next in line. Will we start seeing the West/East aspects release this week - there is a good chance with the cloudy and warm weather forecast. So what to watch for if headed to the mountains? Is the snowpack frozen or is it mushy and wet? That's the key.

Cloud cover: Starting last Friday night, cloudy skies have been trapping in the daytime heat and severely limiting the amount of overnight re-freeze. Although the breezy winds have helped combat this, the pack is still loosening up and becoming weaker. This trend is expected to continue with the forecasted warm, cloudy conditions. Aside from the avalanche concern - many folks have been traveling on glaciated terrain - snow bridges over crevasses are sagging and punching through is becoming more likely.

WET SLAB, WET LOOSE, GLIDE AVALANCHES and CORNICE FALLS:

These are the different characters of avalanches that occur with the melt-down or shed cycle during springtime. Things to keep in mind if headed out:

  1. Did the snowpack re-freeze overnight in your location? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
  2. Are you punching through a shallow crust into wet soggy snow as in the photo below? Also a sign the snowpack is weak and could avalanche.

  3. Do you see any recent avalanches.
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
  5. Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down.
  6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

 


Yesterday, this was the only recent avalanche noted - a small glide on the lower South face of Tincan 

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Secondary Concern

Glide avalanches are still releaseing here and there - we saw one yesterday pictured above. Watch for glide cracks and avoid being under them as they can release at any time.

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Additional Concern

Upper elevation Northerly aspects warmed yesterday enough to moisten the top 4" at 3,800'. This trend is expected to continue with the forecast warm, cloudy conditions. With the added warmth of the pack in these shaded zones, increased stress on underlying weak layers will be occurring. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6' deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the snowpack warms up, these weak layers could re-activate and triggering a slab avalanche is possible. This is a low probability, high consequence problemKeep these points in mind:  

  • It will take someone hitting a 'thin spot' in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall
  • There may be no signs of instability before the slope breaks
  • Several tracks may be on a slope before it releases
  • Stability tests may not produce any notable results

Mountain Weather

Overcast skies and a breezy East wind were over the area yesterday. Over the past 24-hours, Easterly ridgetop winds have been averaging between 10-20mph with gusts to 30mph. Temperatures were up to 50F below 2,000' and up to 36F along the 4,000' ridgelines. All the precipitation, light rain, so far has stayed far to our South.

For today, Sunday, mostly cloudy skies are expected that will continue to hold in the warmth. Ridgetop winds from an Easterly direction will be in the 10-15mph range. Temperatures should stay warm, increasing with daytime warming to 50F below 2,000' and 30-35F along ridgetops. Overnight limited cooling is expected with temperatures dropping to ~40F below 2,000' and ~30F along ridgetops. 

For Monday: A weak low pressure moves through that will bring a chance for light rain to 2,500'. Temperature and winds are expected to remain very similar to Sunday, the main change being increased chance for light precipitation and thickening cloud cover. A series of small disturbances will continue to move through during the workweek, keeping skies cloudy and temperatures warm.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 45  59 
Summit Lake (1400') 42  18 
Alyeska Mid (1700') 43   53 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 33  NE  12  30 
Seattle Ridge(2400') No Data  SE  13  25 

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: Apr 11, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenWide swaths of open river in the Placer Valley. Travel with extreme caution!
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: ClosedClosed for the remainder of the 2017 season.
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
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