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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 14th, 2014 - 7:00AM
Expires
Wed, January 15th, 2014 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Today we have a CONSIDERABLE avalanche danger  on steep slopes (over 35 degrees) at the upper elevations. This elevated danger is in areas that receive 10″ or more of new snow. There is a MODERATE danger below treeline and in areas receiving less snow accumulation. As of this morning, we have around 6-8″ of new snow which has come in with strong East winds. This has not only created wind slabs up to 10-16″ thick, but may also be enough to overload weak snow near the ground. If these weak layers are overloaded, the resulting avalanche could be 3′ deep with wide propagation. Hence – steep slopes with wind deposited snow are places to avoid today.

Safer places to recreate will be the flats and lower angle slopes (less than 35 degrees).

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Tue, January 14th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

The combination of 6+” of new snow overnight (with an additional 3-5″ today) and strong Easterly wind will give us a classic storm snow avalanche situation. Due to the wind, we should see most of the storm snow avalanches in the form of wind slabs. Expect these to be in the 10-16″ range and likely becoming more sensitive, and thicker, with elevation.

Sluffing in the new snow as well as soft slabs in areas out of the wind will be possible. Temperatures have been warming during snowfall which will give the new snow an upside down nature. The warm temperatures will also help the new snow stick to itself as well as the old snow surface and these storm snow instabilities should settle out rather quickly. Hand pits are a good way to suss out these surface instabilities.

Stepping down:
Keep in mind that any storm snow avalanche has the possibility to trigger a larger slab 2-3′ deep that breaks in the weak snow near the ground.

Lower elevations – below 1,500 feet: 4-6″ of wet snow has fallen on surface crusts. Watch for very steep slopes to have some wet snow point release avalanches and shallow slabs.

Avalanche Problem 2
  • 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

The shock of up to an inch of water weight (~10″ of snow) onto our tenuous snowpack will be as much of a concern today as the storm snow issues mentioned above. This load is not huge by any means but areas with wind loading may see double the load – and that is substantial.

For the past two weeks we have seen the weak snow that makes up the bottom foot of the snowpack slowly adjust to the 2-3′ dense slab above it. Will this storm reactivate those buried weak layers? With each passing storm that is the question. This storm is likely not enough to induce a natural avalanche cycle, but in specific areas with greater snow amounts and wind loading the scale could be tipped. 

To reiterate the Bottom Line – upper elevation steep slopes with wind loading are key areas to avoid today. 

Weather
Tue, January 14th, 2014

It is a pleasure to finally report some new snow. We had 6″ fall last night (.6″ water equivalent) and expect another 3-5″ (.4 water) through the day. This is at the mid-elevations (treeline) so greater amounts are likely above treeline.  Temperatures on the ridgetops have averaged in the upper teens F during the past 24-hours with sea level temperature in the mid 30’s F. Ridgetop winds have been 20-30mph with gusts up to 64mph from the East.

Today another system is developing that will add a shot of snow (3-5″) above treeline with a rain/snow mix below ~700′. Associated winds will be Easterly in the 30mph range with stronger gusts. Temperatures should remain warm with ridgetops in the low 20’s and sea level upper 30’s F.  

For anyone keeping tabs on the extended forecast, it is clear we are beginning a transition to a large scale warm southerly flow with embedded disturbances. This will bring off and on precipitation to our area. How much snow and/or rain is determined by where these disturbances develop so stay tuned.

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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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