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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 5th, 2015 - 7:00AM
Expires
Tue, January 6th, 2015 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is MODERATE in the Alpine (above 2,500), where dense slabs 1-3′ in depth could be triggered in steep terrain today.   This is a low likelihood/high consequence scenario, in that avalanches, if triggered, have the potential to injure or bury a person.

The danger is LOW at Treeline (1,000-2,500′), where avalanches are unlikely.

Below Treeline (sea level to 1,000′) there is No Rating due to insufficient snow coverage.

Special Announcements

Conditions at Hatcher Pass led to a few close calls over the weekend.   Weak snow at or near the ground have produced large human triggered avalanches.   Click HERE for video and photos of these avalanches.   These are great examples of persistent weak layers producing large avalanches several days after loading events.   If you are heading up to Hatcher check http://hatcherpassavalanchecenter.org/ for up to date snow and avalanche information.

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Join us for our final Fireside Chat this Thursday, January 8th,  in Anchorage! Topic: Mountain Weather and Snowpack. We will be taking a close look at the current state of the snowpack at Turnagain Pass along with a look into “when is it going to snow?”.

Mon, January 5th, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Layers of weak snow continue to linger below the surface.  On Turnagain Pass the predominant layer of concern is buried surface hoar roughly 2 feet down.  This setup exists mainly above 2,500’.  In the Girdwood Valley and Summit lake areas that layer is facets and is less even in its distribution.  While it has been over 2 weeks since we have seen significant precipitation and about a week since significant winds have loaded slopes, the potential still remains for avalanches to occur on these buried weak layers.

The likelihood of triggering an avalanche anywhere from 1-3 deep is on the low end of the scale.  However, if one were to trigger an avalanche there is still the potential for avalanches to propagate across slopes and be large enough to carry, injure or bury a person.

Most surfaces are firm and supportable around the forecast area.  Slabs are generally strong and can support a lot of weight.  Trigger points in the form of shallow snow and steep rollovers are the most likely areas to initiate an avalanche today.  Slabs of this hardness can break above you making escape very difficult.

If venturing onto steep terrain practice good travel habits:
Expose only one person at a time
Utilize islands of safety for spotting and re-grouping
Identify escape routes in the event of a slab releasing
Communicate route decisions and plans within your group effectively
Be aware of groups above and below you and avoid exposing other groups to avalanche hazard

Additional Concern
  • 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

An “outlier” concern today are old wind slabs.  High winds of a week ago created very dense slabs on the surface as thick as 1 foot.  These slabs have shown to be generally non-reactive.  However, it is still worth keeping these slabs in mind especially if getting onto steep (>40 degree) unsupported slopes.

Weather
Mon, January 5th, 2015

Clear, cold and calm was the name of the game yesterday.   Temperatures were more seasonable with ridgetop stations reporting in the teens F.   Winds have been light generally out of the Northwest and no new precipitation has fallen.

Today expect similar conditions, as a large ridge of High pressure continues its dominance over mainland Alaska.   Temperatures at ridgetops will be in the 20 degree F range.   Some valley locations will experience a strong inversion this morning and keep temps in the single digits F where valley fog has developed.   Winds will be light out of the East at 5-10mph.

Clouds should move over the area Tues night as a large band of moisture attempts to push up towards Southcentral AK from the South.   The next chance for precipitation will come mid to late week as the blocking ridge looks to potentially break down.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 13 0 0 33
Summit Lake (1400′) 2 0 0 6
Alyeska Mid (1700′) 13 0 0 25

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 WNW 3 15
Seattle Ridge (2400′) 14 VAR 6 22
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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.