Storm snow avalanches will be the main concern as a quick moving system is impacting the region. Snowfall totals so far are 4+” in Girdwood Valley and 1-2″ at Turnagain Pass. Another 6-8″ is expected through the day (to sea level), yet Turnagain Pass may only see a few more inches. The snow is very low-density and should sluff easily on steep slopes, both naturally as well as human triggered. The moderate to strong winds with the storm have a Southerly component, which is unusual and could create wind slabs in unusual places. Wind slabs could be up to a foot thick and will depend on how much snow has fallen. If found, they are likely to be soft and easy to trigger. In areas seeing more than 6″ of new snow, and definitely areas with 10″ or more, watch for soft storm slabs.
It is a day to pay attention to how much new snow has fallen and what the winds are doing. If you are in an area with only a few inches of new snow, the main concern will be finding an old wind slab or triggering an avalanche in deeper weak layers of the pack (discussed below). Quick hand pits will be a good tool for assessing new snow amounts. They are also good for determining if there is stronger snow over weaker snow – signs that a wind or storm slab is present.
Image below is from Fresno Ridge yesterday (Summit Lake area). This small pocket triggered on a test slope in the trees shows Friday’s new snow overloading a faceted weak layer sitting on a crust. Be aware of old weak layers that may become overloaded with today’s new snow. (Photo: Chis McNeil)
The snowpack is very weak in general and we need to keep in mind that larger slides breaking in persistent weak layers could occur; even though most of today’s activity will be relegated to the new snow. The new load from today is adding to the weight from Friday and earlier in the week. This is incremental loading and can slowly overload weak layers. Furthermore, new snow avalanches have the potential to step down to these layers. In the upper elevations a layer of buried surface hoar from Jan. 21st continues to show signs of reactivity and in the mid-elevations a layer of facets over a melt-freeze crust is suspect.
Deep Persistent Slabs: At the high elevations above 3,000′, deeper persistent layers could ‘wake up’ if the wrong spot is found. Old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass.
Photo below is from the mid-elevation slopes of Cornbiscuit (Korn/Biskis) yesterday where a layer of very weak facets sit on a crust below the February snow.
Sunny skies were over the region yesterday. Ridgetop winds were 15-25mph from the Northwest before backing off around noon. Temperatures were in the teens at most locations. Overnight a low pressure has moved in from the West bringing light snowfall. Between 2-4″ of snow has fallen as of 6am (.1 and .2″ of water equivalent). Winds shifted to Easterly with the snowfall and are blowing Southerly 10-20mph.
Today, snowfall will continue as the low pressure moves Eastward. We are expecting an additional 4-8″ of low-density snow (.3-.4 water equivalent) through the day before the system moves out this evening. The storm track is favoring the Hatcher Pass and the Front Range (Talkeetna Mtns, Western Chugach), where upwards of a foot of snow is forecast. Ridgetop winds should remain Southerly in the 10-20mph range before turning Westerly and remaining around 15-20mph overnight. Temperatures will be in the upper 20’sF at sea level and lower 20’s along ridgetops.
For Tuesday, clearing skies and windy, cold conditions are expected. Strong ridgetop winds should bring in cold air (single digits) from the Northwest. Stay tuned as to how these winds develop on tomorrow’s forecast.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||25||1-2″||0.05||68|
|Summit Lake (1400′)||20||1-2″||0.1||30|
|Alyeska Mid (1700′)||20||4″||0.2||63|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||17||Southerly||16||58|
|12/06/19||Turnagain||Avalanche: Sunburst||Billy Finley|
|12/04/19||Turnagain||Observation: Sunburst||A.Johnston-Bloom/ W.Wagner/ R.Van Luit Forecaster|
|12/03/19||Turnagain||Observation: Hippy Bowl||Nick Langowski|
|12/01/19||Turnagain||Observation: Tincan, All elevations||Eric Roberts|
|12/01/19||Turnagain||Observation: Tincan||Andy Moderow|
|11/30/19||Turnagain||Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge||Eric Roberts|
|11/29/19||Turnagain||Observation: Sunburst Ob #2||Aleph Johnston-Bloom Forecaster|
|11/29/19||Turnagain||Observation: Sunburst Ob #1||Aleph Johnston-Bloom Forecaster|
|11/27/19||Turnagain||Observation: Tincan||Aleph Johnston-Bloom Forecaster|
|11/25/19||Turnagain||Observation: Sunnyside||Graham Predeger Forecaster|
Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: firstname.lastname@example.org
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