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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   Heather Thamm  
Saturday, January 6th 2018
Created: Jan 5th 19:28 pm
Summary and Current Conditions

A storm over the New Year’s holiday brought about a foot of new snow to the Summit Lake zone over a 4 day period. This weather event came with strong winds, warm temperatures, and rain to about 2000’. This snow also fell on a thin weak snowpack and buried a widespread layer of surface hoar. Very little natural avalanche activity was observed with the exception of some small mid-storm slabs on steep features. Temperatures near the end of the storm cooled down and formed a melt/freeze crust to 2000’ with about 3” of light dry snow on the surface. On Friday, January 5th, moderate Easterly winds picked up mid-day and were seen transporting loose snow onto leeward aspects. Although there wasn’t a lot of snow available for transport, shallow wind slabs were forming and this additional load could be adding more stress to deeper more dangerous avalanche problem, Persistent slabs. Heighten avalanche conditions exist in the upper elevations above 2500’ and it will be important to evaluate snow and terrain carefully. Obvious clues like shooting cracks and collapsing "whumpfing" may or may not be present. 

Should you see changing weather this week, such as rapid loading due to new snow, rain or strong winds, the avalanche hazard could quickly become elevated, and it will be best to avoid avalanche terrain all together. Since this report is a weekly summary, PLEASE be sure to follow the Turnagain Pass advisory for current weather and avalanche conditions. Please 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

The best way to describe the snowpack at Summit Lake is variable and thin. Summit Lake has only seen about a third of the total precipitation that Turnagain Pass has seen this season. The overall height of snow ranges from scoured along windward ridges to 4+’ feet deep snowpack on leeward aspects. Below 2000’ several crusts can be found where there is little potential for triggering an avalanche. 

In upper elevations there are several weak layers worthy of concern. A widespread layer of surface hoar was buried below the New Year’s storm snow and was reactive in tests near the tail end of the storm. This observation found propagation potential in stability tests on a West aspect of Tenderfoot at 2800’. Very little info is known about the distribution of this layer, how well it is adjusting, or how reactive it remains. As you travel look to see how this new snow is bonding to the weak surface snow utilizing hand shears or snow pits.   

Also be aware of weak faceted snow that sits near the ground under a hard slab in upper elevations, above 2500.’ These basal facets were formed in November and buried under several feet of snow in early December. It has been over three weeks since any avalanche activity has occurred on this weak layer, but due to the longevity of facets, this avalanche problem is slow to heal and tricky to navigate. You will likely not get any warning signs such as “whumpfing”, shooting cracks, or collapsing. Initiating such an avalanche can be stubborn to trigger and multiple people can ski/ride a slope before finding a trigger spot. Likely trigger spots will be thinner areas of the snowpack near rocks or on steep convexities. The consequences of this problem are proportional to the terrain you choose. The larger the terrain the higher the consequences should it release. Maintaining a cautious mind-set and conservative terrain choices are recomended.  

 

An extended column test that propagated on buried surface hoar at Tenderfoot. 

 

An observation from Frenso Ridge last week with basal facets found near ground. 

 

A slab that released mid storm is seen on left and old debris from the early December storm is in large gully.  West facing aspect of Lonestar Peak in Summit Lake.

 


Secondary Concern

Easterly winds 10-25mph on Friday, January 5th were seen loading leeward aspects and forming new wind slabs on leeward features. Before these winds kicked up there was about 3" low density snow available for transport. This is just enough wind and snow to create shallow tender wind slabs and add additional stress to deeper layers within the snowpack. Triggering even a small wind slab could step down to a deeper, more dangerous layer within the snowpack. Also be aware of cornices that may be bigger than you realize and can break further back than expected. 

A large plume of blowing snow on Twin Peaks, just North of Summit Lake, was seen on Friday, January 5th.  

 

 

Wind devil on Southern shoulder of Moose Mountain on January 5th

 


Mountain Weather

A storm that impacted the Kenai Mountains over the New Year’s weekend left 8 -12” of new snow in the Summit Lake area, 1.0” SWE at Summit Lake Snotel. This storm came with warm temps, a period of rain to about 2000’, and strong Easterly winds. Temperatures reached the mid 30F’s mid storm and then cooled to below freezing temperatures with the last few more inches falling as light dry snow. Later in the week skies cleared and temperatures averaged in the low 20F’s the teens F’s for several days. On Friday January 5th, skies were clear and moderate Easterly winds picked up in the afternoon and continued overnight into Saturday.

For the weekend snow flurries are possible, but only a trace of new snow is expected. Easterly ridge top winds 10-20mph should decrease to light and variable by Sunday. Temperatures should stay below freezing in the mid to high 20F’s through the weekend. The long term forecast for early in the week is calling for cooler temps and no significant snowfall or winds. 

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. 

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: Apr 22, 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: Open
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: Open
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: Open
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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If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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