Avalanche Advisory: Monday - Mar 12, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON March 13, 2018 @ 6:42 am
Avalanche Advisory published on March 12, 2018 @ 6:42 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

The avalanche danger will remain MODERATE today at all elevations. Small loose wet avalanches will become increasingly possible on sunny aspects as the snow warms. Weak layers of sugary facets buried under the most recent storm snow continue to show potential for failure and though unlikely, large persistent slab avalanches are not out of the question. Evaluate the snow and terrain carefully to identify areas of concern.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
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Temperatures will be a few degrees warmer today under sunny skies. As the snow becomes wet and saturated, especially in steep rocky terrain below about 11,000’, loose wet avalanches will become increasingly possible. Rollerballs and small point releases are signs that stability is deteriorating. Sinking into wet snow deeper than your ankle is also a good clue that it is time to get off of that slope. Timing is everything. You can avoid the problem all together by being off of sunny slopes before the snow thaws too deeply.

Avalanche Problem 2: Persistent Slab
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The layers of weak sugary snow buried by the storm on 3/1 have continued to show potential for failure in snowpack tests. New observations show that avalanches released within these layers as recently as 3/8. In the Mammoth area, where the most snow fell during the last major storm, some of these layers are buried over 3’ deep which makes triggering them very difficult. However, more and more observations are showing weak snow that is less than a meter below the surface, which is shallow enough for a skier to potentially trigger. It’s a low likelihood-high consequence situation. Avalanches may be hard to trigger, but could be quite large. You will have to dig down and perform your own stability assessment to know what these weak faceted layers are doing on the slopes where you want to play. You will most likely find them on sheltered E-N-W aspects. In isolated areas where the sun will warm the snow over top of these layers today melt water could further weaken the snowpack. Pay close attention to the snow under your feet.

advisory discussion

Several loose wet avalanches were observed yesterday on E and S aspects in steep rocky terrain during the first major warming event to affect the snowpack in recent weeks. Most ares had a good solid refreeze overnight. Light winds may help keep the snow surface cool at upper elevations. That’s all good news for the likelihood of wet instabilities today. But as temperatures climb a few degrees warmer this afternoon loose wet avalanches will still be possible. By mid day on steep sunny slopes water saturated snow may result in wet sloughs. Even smaller and slow moving point releases can be hard to escape and can carry you into a dangerous situation, like a terrain trap. Time your day to be off of solar aspects before they get too warm. E aspects will warm first, then S, then W as the sun moves across the sky. Lower elevation northerly aspects may warm just enough for small loose wet avalanches where rocks and trees reflect the heat back down at the snowpack.

Persistent weak layers of sugary faceted grains in the snowpack continue to show potential for failure under stress. Going off of what little information we had, we have been concerned about sugar snow that was buried deeply by the recent storm on 3/1-3/4. Those areas where weak snow is buried over a meter below the surface seem to be trending less and less likely to result in an avalanche. However, snowpack tests continue to indicate the possibility for failure where facets are buried less than a meter deep. That’s concerning because at that relatively shallow depth an unlucky rider might still be able to trigger a large avalanche. Avalanches released from a rider’s tracks as recently at 3/8 near TJ Lake in Mammoth, so the problem isn’t going away yet. To hedge your bets, dig down and perform your own stability assessments if you intend to play on W-N-E aspects that had snow prior to 3/1, especially if brush and small trees that could act as anchors in the slab are sparse or covered over. It’s a good idea to know what these layers are doing before more snow comes later this week, adding more weight to the top of the snowpack.

In isolated areas where the slab above the facet layer will be warmed today, on E and W aspects, melt water may trickle into the sugary snow and weaken it further. Don’t play on slopes after they begin to show significant warming. Sinking deeply into wet snow and large rollerballs are good clues. Dig down and know what the snowpack looks like under your feet.

Weather and CURRENT CONDITIONS
weather summary

Today`s conditions will be drier and rather benign with increasing cloud cover tonight and breezes as low pressure continues to drop down the Pacific Coast. Temperatures will be near average through the early portion of this week before falling below average later in the week. A stronger system will bring gusty winds, rain, and snow Tuesday and Wednesday. Unsettled conditions will continue into the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy then becoming sunny. Clear then becoming partly cloudy. Slight chance of snow. Mostly cloudy. Chance of snow and rain.
Temperatures: 44 to 50 deg. F. 28 to 33 deg. F. 38 to 46 deg. F.
Mid Slope Winds: S SW S
Expected snowfall: 0 in. From a dusting up to 1 in. Up to 4 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy then becoming sunny. Clear then becoming partly cloudy. Chance of snow. Mostly cloudy. Snow likely.
Temperatures: 37 to 42 deg. F. 23 to 29 deg. F. 31 to 37 deg. F.
Ridge Top Winds: S SW SW
Expected snowfall: 0 in. From a dusting up to 1 in. 1 to 4 in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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