Avalanche forecast

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
View on map

Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering a large, 1-3 foot thick avalanche remains possible. Very steep, rocky areas where the snowpack is thinner—less than about 4 feet thick—are most suspect. Intense sunshine and warm temperatures may cause small, loose snow avalanches on slopes that directly face the sun. These slides could "step down", triggering larger avalanches as they move downhill. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    We are still leery of persistent weak layers (facets and/or crusts, and occasionally surface hoar) buried in the top 3' of the snowpack. These layers have produced several avalanches over the past two weeks (Dollarhide, Galena Summit, Smiley Creek, Beaver Creek, Sawtooths, Banner Summit). They seem most reactive on sunny slopes where facets are associated with crusts (video, photo), but two fairly recent large avalanches occurred on shady aspects in the Sawtooths.

    Yesterday, experienced skiers backed off their objective in the Sawtooth Mtns due to concerns about how the past few weeks of snowfall has bonded to the hard crusts and surfaces beneath. Monday, experienced guides felt and heard a large collapse on a sunny ridgeline in the northern Boulder Mtns and switched to a more conservative plan B. Also Monday, I saw a natural persistent slab avalanche that failed in an area with a very thin snowpack in the Boulder Mtns; it released when hit from above by a small wet loose avalanche (see Problem 2). The warm temperatures and intense sunshine are adding uncertainty to the persistent slab stability equation.

    Finally, we can't yet completely forget about the weak early-season snow buried deep in the snowpack. 

    How can we manage or avoid this fairly complex, unpredictable problem?

    • Triggering a large avalanche is most likely on slopes steeper than about 35 degrees that are above about 8500' in elevation. These elevations received the most snowfall and wind-transported snow during last weekend's storm.
    • Rocky terrain where the snowpack is thinner gets your skis or sled track closer to the weak layers in question and is more suspect. Avoid craggy slopes that are peppered with exposed rock. 
    • Picture the consequences of being caught in an avalanche before committing to riding or skiing that steep slope. If a 2-3 foot thick slide released, would you be carried through trees or rocks? Would you be buried in a creek bottom or gully where snow can pile up deep?

    ADDITIONAL DISCUSSION:  Last weekend, the combination of new snow and wind built isolated slabs in exposed terrain. These wind slabs are stabilizing, but some formed above weak snow surfaces (facets and/or crusts) and could be sensitive to the weight of you or your machine.  Recognize that wind-loading also adds stress to the weak persistent layers described above. Relatively small, human-triggered wind slabs could "step down" to these deeper layers, producing a larger, more dangerous avalanche. You are most likely to trigger a wind slab in steep, rocky "extreme" terrain. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Today's warm temperatures and sunshine could cause small, loose snow avalanches to release naturally. These slides can be dangerous on their own in rocky, consequential terrain, and they can trigger larger slab avalanches as they travel downhill. We saw evidence of this earlier this week in the Boulder Mountains (observation here, photo to right and here). Wet loose slides are most likely to release in very steep, rocky terrain that directly faces the sun and is sheltered from the wind. This type of instability follows the sun around the compass, beginning on E-SE aspects in the morning, moving to SE-S facing terrain near noon, and finishing up on SW-W aspects later in the afternoon. Fortunately, this hazard is easily managed:

    • Watch for rollerballs and pinwheel moving down slopes facing the sun. This is a sign the snow surface is heating up, and wet loose activity may not be far away.
    • Minimize your time spent basking in the sun below large avalanche paths that fit the description above. While the T-shirt conditions make these great places to take a break, be sure you're out of the firing zone in case slides release on their own above you. 

    The heat is also affecting the large cornices that have formed throughout the season. These beasts sag and can break during the heat of the day. Yesterday, I saw chunks from a recent natural cornice failure in alpine terrain in the Smoky Mtns. Cornice fall can be a great trigger for the persistent slabs described in Problem 1. Give cornices a wide berth if you're traveling on ridgelines, and minimize the time you spend on slopes directly beneath large cornices.

    (3/1/2021) A small wet loose slide stepped down on a SE aspect near 9900' on Easley Peak, causing a bigger slab avalanche. This area had a very thin - and likely very weak - snowpack.

Avalanche Discussion

"WARMING"

What happens to snow when sunshine or ambient air temperatures cause it to warm? As is usually the case, the answer is "it depends."

The air temperature can warm dramatically from very cold (let's use -30 F as an example) to cool (say 20 F) and not impact snow stability. Forty or fifty degree F swings like this happen all winter long around Stanley and Smiley Creek, but we don't see avalanches come crashing down to the valley floor whenever the temperature warms by 30-50 degrees over the course of a day.

However, snow behaves more like a fluid as the material temperature rises to near freezing (0 degrees C, or 32 F). This causes it to bend and deform. When deformation increases in the snow at and near the surface, it can affect the stability equation involving weak layers that are staying cold well below the surface. Adding a foot of new snow would cause a bigger change in the stability equation, but the effects of temperature changing the slab properties near the surface are something to consider when choosing terrain to ski or ride today. This same phenomenon can also make cornices behave unpredictably (fall off!) during sunny spring warm spells. 

As the snow temperature reaches freezing and it begins to melt, the properties change dramatically.  Small "point releases" of wet snow entrain more snow and move downslope, causing wet loose avalanches in steep terrain. We're not seeing enough melt-water move into the snowpack now to worry about wet slab avalanches...yet. That's probably coming later this year, stay tuned. 

 

Regions covered