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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   Aleph Johnston-Bloom  
Friday, March 2nd 2018
Updated: Mar 3rd 7:23 am
Created: Mar 2nd 17:31 pm
Summary and Current Conditions

It has been an eventful week in the Summit Lake area.  Snow over the past weakend and early in the week was followed by strong winds. This overloaded the persistent weak layers that have been the theme of the Summit snowpack this season and resulted in a natural avalanche cycle on the 27th and 28th. There was also a close call on Tenderfoot on the 27th when skiers triggered a large avalanche while skinning up the ridge. This avalanche failed in weak facets under the January rain crust. The slab was very hard, wind-affected snow, the avalanche was triggered in a thin spot and there were no signs of instability before it released. The presence of the persistent weak layers should be in the forefront of all terrain choices, especially with more snow in the forecast this coming week. Recent avalanches are the best data to indicate the potential for more avalanches. The weak layers in Summit have proven themselves guilty! Extra caution is advised. 

Snow totals for the week were in the 8-12" range (0.7 SWE ). The winds were from both the South and the North and gusted into the 40s and 50s. The Northerly event was the trigger that really tipped the balance and caused the natural avalanche cycle. There is snow in the forecast for much of the week to come. At this point the most notable storm looks to be starting Wednesday and continuing into Thursday. Paying attention to changing conditions will be key. New snow, wind loading or warming could all increase the hazard due to the weak snowpack in this region. 

This report is a weekly summary, so PLEASE be sure to follow the Turnagain Pass advisory for current weather and avalanche conditions. Help us keep tabs on the Summit area and if you see any avalanche activity send us an observation HERE. Thank you to everyone who has already submitted observations this season - you can see those HERE!


Primary Concern

This past week both natural and human triggered avalanches failing on persistent weak layers occured. This is cause for concern. For most of the season the snowpack in Summit Lake has been described as thin, variable and containing multiple weak layers. Buried surface hoar and facet/crust combination have been tracked and stability tests have continued to indicate that there was the potential to trigger an avalanche. This week proved that. The new snow and strong winds overloaded the weak layers and a couple of skiers on the skin track near each other also tipped the scales. The avalanche on Tenderfoot had very hard surface snow (wind sculpted sastrugi) over the weak facet/crust combination and was. Now that there is very hard wind-affected snow over most of the terrain in the area, there is the chance that this type of avalanche could be triggered again. This hard snow over weak snow may be covered up by new snow this week and it will be important to remember what is lurking below. Hitting the wrong spot could have high consequences. The presence of facets and buried surface hoar in the Summit snowpack continue to make it suspect. Likely spots to trigger an avalanche will be thin spots, particularly at convexities and near rocks.  With a variable snowpack like this, it is possible that the first person to ski or ride a slope does not trigger an avalanche but the 4th or 10th does. An avalanche could be large and unsurvivable.

Wind slabs:  Wind during or after new snow can quickly form wind slabs, particularly on leeward slopes at upper elevations.  Be on the lookout for "pluming" on ridgelines or blowing snow.  Watch for smooth, pillowed looking snow, shooting cracks, and snow that sounds hollow or drum-like. Stiff, supportable wind slabs often break above once you are well out onto the slab. There may be old stubborn wind slabs from winds this week that could be triggered on steep, unsupported, leeward slopes. 

Storm slabs:  If new snow totals start to pile up, be on the lookout for how well the new snow is bonding to the old snow below.  If storms are warmer than forecast be aware that rain on snow can quickly overload the snowpack. 

Loose snow avalanches (sluffs): On steep slopes protected from the wind expect new snow to sluff easily. These loose snow avalanches may be fast running and entrain snow quickly. 

Solar radiation: The sun is now strong enough to warm the snowpack on southerly slopes.  Warming can make persistent slab avalanches more sensitive to human triggers, particularly later in the afternoon.  Watch for sunny warm days between the storms and look for roller balls and wet loose avalanches if there is a quick warm up after new snow. 

 

 Crown profile of the skier triggered avalanche on Tenderfoot.

Trigger point in the slab was only 10 inches thick

Wind pluming on February 28th

 Natural wind triggered avalanches on Summit Peak, February 28th

Natural wind triggered avalanche on Fresno, February 28th

 


Mountain Weather

Last week was a combination of snow and wind, colder temperatures and sunshine. Snow totals ranged from 8-12" of new snow. Temperatures were in the 20Fs to single digits. Winds were both Southerly and Northerly and gusted into the 40s and 50s. The major wind event on the 28th was Northerly. 

For the weekend there is a chance of snow Saturday and then sunshine in the forecast on Sunday. Early in the week there is again a chance of snow but a more significant storm is possible mid week. From the National Weather Service: With the surface low tracking from the Barren Island north up the outer coast of the Kenai Peninsula and the support of a strong upper level trough and good cold air advection, this system look like it has good snow potential for much of Southcentral Alaska Tuesday night and Wednesday. 

Temperatures are forecast to be in the teens and mid to high 20Fs this week with variable winds as the storms move through. In the long term forecast there is discussion of another storm for the next weekend. Stay tuned!

Stay tuned to the CNFAIC weather page for an updated weather forecast each day. The best way to see if it's snowing at Summit Lake is to look at the RWIS webcam snow stake HERE and the NRCS Snotel site HERE. *The above MP 45 station is the best ridge top temperature information. This weather station is in a sheltered area and wind data is typically less than the actual ridgetop winds. Also look at Sunburst Weather Station in Turnagain for a comparison.

Check out the wind speeds from the past week. 

This is a general backcountry avalanche advisory issued for Summit Lake Area 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

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.

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