Thursday, February 22nd 2018 5:51 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
The avalanche danger is MODERATE above 1,000' on all aspects. Human triggered slab avalanches 1-2' thick remain possible. Be aware of a few inches of new snow combined with wind that may form fresh isolated wind slabs in the Alpine. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche.
|Show the Complete North American Avalanche Danger Scale|
|Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.|
Triggering a slab avalanche 1-2+ feet thick continues to be our main concern. Today 3-5” of new of new snow and moderate winds (Easterly becoming Westerly) may add stress to the overall snowpack, but not enough to elevate the danger rating. Several weak layers are buried within our snowpack at varying depths and elevation bands. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in test pits above 2000’, and we’re also tracking a layer of facets over a melt-freeze crust in the mid elevations. Persistent slabs are becoming more difficult to trigger with time, but a large and unmanageable avalanche is still possible. Today watch for active wind loading on all aspects and be aware that red flags such as “whumpfing” may not be present before a slope releases. The most likely place to find this avalanche problem are slopes that have not seen significant traffic this season.
Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could 'wake up' if you find the wrong spot above 3,000' in the Alpine. At these high elevations, 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.
Propagation on buried surface hoar and facets was found in several location on Eddies earlier this week.
New wind slabs will depend on how much snow we see today and if winds are activity moving snow around. Ridgetop winds from the East are expected to change to a Westerly direction this afternoon and remain in the 20's mph. Not much old snow is available for transport, and only a few inches of new snow is forecasted. Expect wind slabs to be small, but they could be tender should you see any obvious clues like blowing snow or shooting cracks. If this is the case steep leeward aspects and cross loaded terrain features will be suspect.
Sunshine: Although the sun is unlikely today, be aware it's that time of year when we need to pay attention to the sun. Following a storm the sun can heat up Southerly aspects and melt surface snow and cause point releases. This heating can also cause a slab sitting on a weak layer to become more reactive. Keep this in mind should a clearing trend behind today’s storm happen sooner than expected.
Surface conditions before today's weather consisted of an inch of loose surface snow on top of variable surfaces (wind affected snow and patches of loose settled snow.)
Yesterday high cirrus clouds moved into the area and skies were broken becoming mostly cloudy by the evening. Ridgetop temps were in the mid 30's and overnight temps dropped back into upper 20F’s. Winds were light from the West and transitioned overnight to an Easterly direction. As of this morning both Seattle Ridge and Sunburst were averaging in the 20’s mph with gusts in the 30’s (East direction.) As of 6am no precipitation has been recorded.
Today a low pressure system is moving through our region with a Southwesterly direction. Snow showers are expected this morning through mid day and tapering off in the afternoon. Snow totals may reach 3-5” (.3” H20) in parts of our forecast zone. This storm is expected to favor Anchorage and the Mat-Su areas. Temperatures at sea level may be in the low to mid 30F’s and this precip may fall as rain to 500 ft. Ridge top winds will remain in the 15-30mph range, starting out as Easterly and transitioning to a Westerly direction this afternoon.
Active Southwest flow will bring several more low pressure systems into Southcentral, Alaska throughout the weekend and into early next week. Each system is followed by a period of clearing skies. Southwest flow tends to favor Cook Inlet and the Matanuska Valley for snow, but precipitation is expected across our region. Temperatures are expected to be near normal and range from the 20F’s into the mid 30s. Rain and/or snow is possible at lower elevations.
*Center Ridge weather station has been producing erratic temperature data.
PRECIPITATION 24-hour data (6am - 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880')||*34||0||0||62|
|Summit Lake (1400')||26||0||0||24|
|Alyeska Mid (1700')||30||0||0||55|
RIDGETOP 24-hour data (6am - 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Sunburst (3812')||30||W --> E||6||34|
|Seattle Ridge(2400')||32||W --> E||8||32|
This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
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 13, 2019 )
|AREA||STATUS||WEATHER AND RIDING CONDITIONS|
|Twentymile:||Closed||Closed. Forest Service is monitoring conditions.|
|Lost Lake Trail:||Open||Please stay on trail to avoid resource damage through forested areas.|
|Primrose Trail:||Open||Please stay on trail to avoid resource damage through forested areas.|
|Resurrection Pass Trail:||Closed||Closed for the 2018/19 season. Next season will be open to motorized use.|
|South Fork Snow River Corridor:||Open|
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