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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   CNFAIC Staff  
Saturday, January 13th 2018
Created: Jan 12th 14:08 pm
Summary and Current Conditions

*Increasing avalanche danger in the Summit Lake area*
12 - 15" of new snow fell on Saturday 1/13 with strong winds, human triggered avalanches could be likely - see report from Tenderfoot and video below.

There is a major pattern shift in the weather from calm and cold to warm, wet, and windy this weekend. This is expected to bring 12-18" of new snow to the Summit area along with strong winds.  The Summit area continues to have a generally thin snowpack, harboring various weak layers, heading into this storm.  Additionally, the "recycled powder" that formed over the last week of cold and clear weather made for great skiing, but will be a weak foundation under any new snow.  Hence, bonding between the new and old snow surfaces are expected to be poor and avalanche danger will rise with increasing new snowfall.  The NWS has high confidence that this storm will produce precipitation for the Summit area, but there is uncertainty around total snowfall amounts.  More information can be found below in the mountain weather discussion.

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
By Sunday night, the Summit area could see 12-18" of new snow before the storm tapers off.  Storm slab avalanches will be a concern if the new snow amounts verify. The hazard will be compounded by an increase in wind during the storm, and could build wind slabs on leeward slopes 2-3' thick.  Observations from last week showed that the new snow will fall on very weak surface snow sitting over various crusts.  This recipe of slab, weak layer, and bed surface are the ingredients for human triggered avalanches on slopes steeper than 30 degrees.
 
If storm snow starts to pile up, careful snowpack evaluation will be warranted to assess the bonding of the new snow to the old.  Be on the lookout for cracking, collapsing, and whumpfing.  These are red flags that the snow is unstable.  Using your pole to probe for strong over weak or "upside down" snow, hand pits, kicking at switchbacks, and jumping on small low-consequence test slopes are all great ways to detect how well the storm snow is bonding to the old snow.  At lower elevations, rain on snow could occur and create a wet avalanche problem. In this case wet loose as well as wet slab avalanches could occur naturally.
 
 
Video from Saturday during storm

 
New snow will be falling on weak surface snow as seen below, surface hoar sitting on near surface facets.
 
 
 
Cracking and collapsing are a red flag that the snow is unstable.
 

Secondary Concern
There were no reports of human triggered avalanches in the Summit area last week, and many folks skied and rode steep slopes without incident.  Various weak layers sit in the snowpack. The two most prominent are the New Year's buried surface hoar, which sits 1-2' below the surface and basal facets near the ground. Snow pit tests are showing these layers are becoming increasingly stubborn and hard to trigger.  However, some pit results continue to show propagation potential.  The new snow could add stress and "wake up" the weak layers.  Additionally, storm slabs triggered in the new snow could step down into older weak layers, producing avalanches that could bury, injure, or kill a person.  The most likely place to trigger an avalanche deeper in the pack are thin spots, near rocks or on steep convexities at elevations above 2500'.  New snow could also make it difficult to identify where these thin spots are this coming week.
 
Keep in mind, no feedback such as collapsing, cracking, or whumpfing may be present when there is a persistent slab avalanche problem. Multiple people might be able to ski or ride a slope without incident before releasing.  Traveling tests such as pole probing and hand pits are also ineffective at identifying deeper weak layers that can cause problems.  The only way to identify areas of weaker snow are to dig in and look at the snowpack structure. Conducting stability tests such as the ECT can be great, but pit results could be highly variable and no single pit can give you the green light, but one may give you the red light.
 
 
Stability tests are still showing propagation potential on older weak layers in the snowpack above 2500'.

Depths are highly variable in Summit, with ridgelines stripped bare adjacent to deeply loaded gullies.  Thin spots, where it will be easier to trigger an avalanche, could be difficult to identify with new snow. 
 
 
 
Surface hoar buried in the New Years storm cycle: An example of one of the weak layers in our snowpack that may still cause trouble.
 

Mountain Weather

The Summit area saw relatively benign weather over the last week, with cold overnight lows dropping from the teens and 20'sF last weekend to single digits and below-zero temps by midweek.  Daily highs stayed moderate, with temps in the upper teens and 20'sF at 1400', and temps in the teens at ridgetops.  Light and variable winds kept surface snow in place, and made for pleasant weather to be out enjoying the snow from the New Year's storm cycle.

A new system rolled in on Thursday and brought with it a significant increase in temperatures and wind.  Temps climbed above freezing at 1400' by noon on Friday, and ridgetop winds were gusting 30 to 40 mph.  Though this storm is rolling in warm and wet, the Summit area has yet to see any precipitation.
 
The storm is expected to continue into midweek next week, though weather models have high uncertainty regarding the exact timing or track of specific storm features.  Temperatures will likely peak on Sunday, with highs in the upper 30's in the Summit area, before dropping back to around freezing by Monday.  This will keep most of the precip in the form of rain at lower elevations, and rain could reach as high 1500' at times.  Elevations above the rain line could see 12-18" of new snow through Sunday evening.  This storm also brings with it significant Easterly winds; expect ridgetop gusts to be as high as 80 to 100 mph.
 
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: Jan 05, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: Open Turnagain Pass motorized area is open. Early season shallow snow cover conditions exist. Please avoid riding on “Rookie Hill“ and other areas with exposed vegetation. Thank you!
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season as soon as conditions warrant.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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