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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, April 17th, 2015 - 7:00AM
Expires
Sat, April 18th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

UPDATED Friday at 3:50pm:

TINCAN AVALANCHE: We just had a report of a very large skier triggered avalanche around noon today on both the North and South side of Tincan. We are currently gathering details; if anyone has any information please email wendy@chugachavalanche.org. At this time there are no known persons involved.

The slides were triggered remotely by a party of skiers on the CFR Ridge, below the top of Common Bowl. Both avalanches were reported to be 2-3′ deep. The North slide may be over 1,500′ wide and took out at least some of the Tincan Chutes area and further West along the ridge, running to the flats below. The South avalanche was in CFR bowl itself, under the corniced ridgeline. Todd’s bowl did not avalanche.

Extreme caution is advised if you are thinking of heading out this afternoon. This includes avoiding avalanche terrain as well as runout zones from slopes above you.

 

The avalanche danger is MODERATE today both in the Alpine and at Treeline. Newly forming windslabs 4-8 € thick could be tender on leeward terrain features. Should a large low-pressure system arrive earlier than expected the avalanche danger could become CONSIDERABLE by early evening. Wet loose avalanches will be possible at lower elevations should surface conditions become saturated due to warming day time temperatures and rain.  Evaluate snow and terrain carefully and pay close attention to changing snow conditions throughout the day.

Special Announcements

We are currently issuing advisories 5 days a week until our final advisory on Thursday, April 30th.   Advisories will be posted at 7 am each day except Mondays and Wednesdays.

Fri, April 17th, 2015
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

Today up to 5” of new snow combined with moderate winds (20-30mph) from the Northeast could form isolated wind slabs up to 8″ thick on leeward terrain features.  On shaded features in the Alpine (where a surface crust doesn’t exist) these wind slabs could stress the most recent storm slab up to 2’ thick. At lower elevations these wind slabs will be forming on a surface crust and could be tender.

Wind slab thickness will depend on how much snow falls today. A large low-pressure system is expected to push into our region this evening. Winds are likely to increase into the 40s mph and an additional 8” of snow is expected this evening. Should this storm arrive earlier then expected the avalanche danger could increase to CONSIDERABLE by early evening.

Careful snowpack and terrain evaluation are required for every group traveling in the mountains. If you find that the snowfall intensity and strong winds are causing rapid loading, keep your slope angles below 35° and avoid large open slopes.

Deeper Persistent Layers:

There are several old weak layers burried deep within our snowpack. Today’s moderate winds and new snow will likely make visibility challenging. Should a window apear making steeper more extreme terrain appealing, condsider that we don’t have a lot of current info about these layers. It has been 6 days since activity has been observed in these deeper layers, but it is uncertain how much additional loading + the right trigger will re-awaken them.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Springtime requires us to pay close attention to how the snow changes throughout the day. We have seen intense solar affect almost every day. This is a reminder that our current snowpack can change dramatically from the morning into the afternoon. Although sun isn’t supposed to be an issue today, it has suprised us over the last few weeks and subtle warming affects are playing more of a role than noticed.

As this storm moves into our area expect rain/snow line to start moving up in elevation and could be as high as 1500’ by Saturday morning. Should the lower elevation snow become wet and saturated wet loose avalanches will be possible.

Turnagain Pass looks more like winter than it has most of the season. The Forest Service is closely monitoring the snow depths and snow density on the motorized side of the road for a potential motorized opening. There isn’t quite enough coverage yet to protect the vegetation below, but check back here should this next storm come in cold.

Weather
Fri, April 17th, 2015

Yesterday cloud cover in the morning was thick and in the afternoon skies became partly sunny at times. Scattered snow and rain showers were observed throughout the day with little to no accumulation. Temperatures were between 30-40F at lower elevations and averaged in the mid 20s F along ridgetops. Winds were calm in the morning increasing to 15-20 mph from the Northeast in the afternoon.

Overnight temps at lower elevations dipped just below freezing and only a trace of precipitation was recorded. Winds were moderate 15-25mph from the Northeast along ridgetops.

Showery rain and snow conditions are expected throughout today. Winds will increase in the afternoon as a large low-pressure system arrives tonight bringing rain and strong winds. Rain/snow line may be as high as 1500′ by Saturday.

PRECIPITATION 24-hour data (6am – 6am)

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34 0 0 75
Summit Lake (1400′) 34 0 0 12
Alyeska Mid (1700′) 34 2 .19 43

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 ENE 13 45
Seattle Ridge (2400′) 26 n/a 17 31
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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.
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