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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   CNFAIC Staff  
Saturday, February 18th 2017
Created: Feb 17th 15:04 pm
Summary and Current Conditions

Elevated avalanche danger exists today (Saturday) and dangerous avalanche conditions could persist through the week in the Summit Lake Zone. Sunday Feb12th through Feb 14th a warm storm front quickly rolled into the area bringing temperatures up into the mid 30F’s with rain/snow line estimated around ~2100’. A breakable crust was formed to this elevation. Temperatures cooled later in the week along with an additional 9” of snowfall recorded at the Summit Lake SNOTEL. In the alpine a total of 15-20” (1.6” of water) fell throughout the week. The Valentine’s storm also brought strong ridgetop winds causing widespread wind loading on a variety of aspects. Several natural avalanches occurred mid to late storm including the West faces of Tri Tip, Butch, and Moose with the slide off of Butch reaching all the way to the lake below. As has been the case most of this season there is still very poor snowpack structure throughout the Summit Lake area. This includes varying slabs 1-6' thick sitting on weak faceted snow near the ground. Also an observation on Thursday confirmed that a layer of buried surface hoar, formed prior to the Valentines day storm, is also lurking under our most recent snow. In addition winds have scoured ridgelines and loaded (top loaded and cross loaded) a variety of aspects. Wind slabs 1-3’ may be sitting an old slick bed surface or on weak snow below (facets or buried surface hoar.) 

It is important to remember that a lot of stress was just added to the snowpack and the snow will take time to adjust to this load. A variety of avalanche problems exist and there is potential to trigger a slab avalanche 1-6’ thick, including a large avalanche that could propagate a whole slope. Due to complexity of the snowpack and recent weather conservative decision making will be important and it will be a good idea to ease into terrain slowly and with caution.

*Don't forget any active weather (snow/rain or winds) will elevate the avalanche danger. The sun has some heat to it. Keep this in mind when traveling on southerly aspects especially on steep slopes or near rocks/vegetation if it becomes sunny. Roller balls are an indicator that the snowpack is getting wet and wet loose avalanches are a sign of a weakening snowpack. Should you observe any red flags (shooting cracks, whumphing, recent avalanches) these are obvious clues the snow is unstable and avoidance of avalanche terrain is recomended. 

During the week, stay tuned on the most current up to date avalanche and weather conditions on the Turnagain Pass daily advisory and the Summit Lake Observations Page! Also, Please help us keep tabs on the Summit area - if you see any avalanche activity send us an observation HERE

 

Crown line of an avalanche off the West face of Butch Mountain. This avalanche ran all the way to the lake below. 

 

Recent avalanche off the South West shoulder of Lonestar

 

2-3 cm thick rain crust at lower elevations. Thins at higher elevations but is present to ~2100'. 

 


Primary Concern

So far this has been the season for persistent slab problems! This week buried surface hoar was found on an East aspect of Fresno 6" below the surface. This was in a protected area around 2000’ and as of Saturday morning an additional 8" has fallen. It is unknown how widespread this layer is throughout Summit Lake, but the Alaska Avalanche School found buried surface hoar on Manitoba last weekend recently buried at the start of the storm. Slabs sitting on this layer may be in the 1-3’ range in the alpine. Surface hoar has been observed throughout our region prior to the Valentine’s storm, and since has been very reactive both in Turngain Pass and Girdwood. Hand pits will be a good tool for assessing the top 1-2’ of snow as you travel. 

Lets not forget about a weak foundation (facets and/or depth hoar) that sits near the ground in many areas of Summit Lake. Due to varying slab depths and hardnesses this is a very difficult avalanche problem to assess and may not give you any red flags (collapsing/whumphing or shooting cracks). As time has passed and more snow has been added to the slab that sits above this persistent weak layer the slab has become more cohesive and stubborn to trigger. This is the kind of snowpack that may allow multiple people to ski/ride a slope without consequence giving you a false sense of stability. However if you find a trigger point, thin spots in the slab, it has the potential to propagate a large avalanche across a slope and break down to the ground. This increases the consequences of being caught and may not be survivable if an avalanche is triggered on this weak layer. This is a good reason to keep your slope angles mellow, below 35 degrees by managing terrain you are directly on as well as the terrain above you. An avalanche of this size has the potential to run a long ways and take whole slopes with them. 

*Be aware of changing weather; rapid loading due to heavy snowfall or blowing snow, as well as rapid warming due to solar hear could make a persistent slab easier to initiate.

Hand hardness profile. Shows the 2-3' thick 1 finger hard slab that sits above 6" of fist hard depth hoar 

 

CT Failure on rotten depth hoar on the East face of Fresno at 2050'.


Secondary Concern

This week strong winds accompanied by recent snowfall (an estimated 15-20”) have formed wind slabs on a variety of aspects due to shifting wind directions (South-East-North.) There is potential for hard supportable wind slabs on exposed terrain features as well as softer wind slabs in more protected areas. Be on the lookout for hard snow over soft snow and remember shooting cracks are an obvious sign of instibliity. Be suspected of unsupported and convex terrain features as well as gullies that may be cross loaded. As we move away from the weather that created this avalanche problem it may be stubborn and not show any red flags prior to being triggered. There is potential for even a small wind slab or cornice to step down an older persistent weak layers near the bottom of the snowpack.

Additional Concerns:

Cornices have been growing and will be touchy especially if the sun appears.  Give cornices lots of space along ridge lines and avoid being directly under these unpredictable hazards.

Loose snow may also be an issue in more protected terrain this week. This is a surface snow instability and will be more likely on steep slopes and it could knock you off your feet in the wrong place. On solar aspects surface snow could be extra touchy if the sun appears  If you notice the surface becoming moist or you see natural point releases triggered by the sun this may be a clue that deeper layers may be easier to trigger as well.   

Ravens Ridge and Butch flagging snow due to high winds. Note the scoured and loaded faces

 

Cross loading and top loading along both sides of this SW ridge on Butch Mountain due to strong winds from a variety of directions. Be weary of wind slabs on all aspect!!

 

Roller balls below treeline formed by strong winds blowing across heavy wet snow. 

 

 


Mountain Weather

Sunday Feb 12th dawned with cold clear temperatures near 0F. As the day progressed temperatures rapidly warmed into the low 30s F due to a large warm storm system in the region. This warming weather brought a mix of snow and rain totaling 3" saturated snow by Tuesday at 1400'. As weather stayed above freezing Tuesday into Wednesday Summit Lake experienced rain to ~2100'. Ridge top winds during this storm were from an Easterly (SE - NE) direction. As the weather cooled into Thursday and Friday ~9” of snow fell to the road level accompanied by moderate SE ridgetop winds. The water weight (SWE) over the last week totaled 1.6” at the SNOTEL Site (1400’.) 

This weekend expect scattered snow showers and temperatures ranging from the mid 20F’s to teens (F.) There is a good chance for patches of blue skies and for the sun to appear at times. Ridgetop winds are expected to be light to moderate throughout the weekend. Precipitation is expected to taper off Saturday. Mild temperatures (in the 20F's) are expected to last through Tuesday with another storm front approaching, potentially, Wednesday. As always this is only a forecast and is important to watch the weather closely.  For the most current weather information visit the CNFAIC weather page HERE.

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 wind and temperature information. Fresno Weather Station will not be operational for the rest of the season. 

Sunny gap between two storm fronts crossing over the Summit Lake area.

 

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: Feb 19, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenAccess is thru the gate on the right side of the parking lot as you drive toward the outhouse. Please park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: Open
Turnagain Pass: Open
Twentymile: Open
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

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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