Avalanche Advisory: Sunday - Mar 25, 2018

THIS AVALANCHE ADVISORY EXPIRED ON March 26, 2018 @ 6:47 am
Avalanche Advisory published on March 25, 2018 @ 6:47 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Human triggered wind slab avalanches will be possible today near and above treeline, where the danger is MODERATE. Evaluate the sensitivity of wind deposited snow carefully. Exposed leeward slopes, especially below ridgelines and the sidewalls of gullies, are the features of greatest concern. Below treeline, where unstable wind slabs are expected to be smaller and isolated, the avalanche danger is LOW.

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.

1. Low

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Below Treeline
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.
Avalanche Problem 1: Wind Slab
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

SW winds continue today though with less snow to transport and decreasing intensity. Large wind slabs that formed over the past few days, when there was ample snow available for transport, are expected to be harder and more stubborn to trigger, though not impossible. Newer wind slabs that formed yesterday and overnight are expected to be smaller but more reactive. Evaluate the snowpack and terrain carefully. Features of concern include steep, unsupported leeward slopes near and above treeline, especially below ridgelines and the sidewalls of crossloaded chutes and gullies.

advisory discussion

Only a few days in and so far Spring has been pretty moody. I’m not saying we didn’t appreciate that big dump last week. That 4-6’ of new glop really boosted the snowpack. Sure, things were pretty exciting there during and just after the squall. In some areas it seemed like everything that could slide slid. The new, heavy snow buried some pretty concerning layers of weak facets even deeper and now that things are settling and becoming supportable it would really take a huge trigger to affect them, unless you can find them much closer to the surface. So that’s all pretty sweet.

But then the winds started ripping. That’s cool, we’re used to that around here, but there was really a lot of new snow to blow around. I mean a lot. SW winds that just wouldn’t quit kept moving snow onto northerly slopes. You’re thinking, “Surely they’ll run out of snow to deposit soon!” But no. They kept building wind slabs into last night. And they even got an inch or so of new snow to play with N of McGee Creek yesterday afternoon. I mean, at least most wind slabs tend to become less reactive with time. The biggest ones that were deposited first should be gaining strength. But with all the “Spring” weather, some newer smaller wind slabs will probably build up even today. Isolated showers could add a little fuel to the fire, maybe up to 1” of new snow. That’s not a whole lot compared to last week. But just remember that the wind can deposit snow on leeward slopes at 3-5 times the the rate it can fall from the sky. So while a lot of these newer wind slabs will be small, it’s probably still possible to trigger them where deposition is favored. Spring seems to be chilling out a little bit and the winds will slow down throughout the day. But you’re going to want to evaluate any wind slabs that you find for sensitivity. Shooting cracks and hollow sounding drifts are not good. Thanks to these cold winds coming from the SW, exposed terrain that faces NW-N-NE-E-SE is most likely to be a problem, especially just under ridges and on the sidewalls of gullies. I’d even double check larger openings in the trees.

As this unstable air mass heads east to hassle someone else “Spring” will start to feel a little more, well, spring like. Sun tans and shades may be the thing in the coming days, but expect any big warm-up to come with it’s own set of avalanche problems. Spring, man. Crazy.

Weather and CURRENT CONDITIONS
weather summary

Snow showers could bring very light additional snow to the Sierra today, but with little accumulation. Drier weather returns this week, with temperatures warming to average Tuesday and well above average for mid to late week.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy. Isolated snow showers. Mostly cloudy then becoming clear. Isolated snow showers in the evening. Sunny.
Temperatures: 24 to 30 deg. F. 7 to 12 deg. F. 25 to 31 deg. F.
Wind Direction: SW to W N N
Wind Speed: 10 to 15 mph. Gusts up to 25 mph. 10 to 15 mph with gusts to 25 mph. Light winds becoming 10 to 15 mph in the afternoon.
Expected snowfall: Little to no accumulation. in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Partly cloudy. Isolated snow showers. Mostly cloudy then becoming clear. Isolated snow showers in the evening. Sunny.
Temperatures: 16 to 22 deg. F. 2 to 7 deg. F. 17 to 22 deg. F.
Wind Direction: SW NE N
Wind Speed: 25 to 35 mph with gusts to 55 mph decreasing to 15 to 20 mph with gusts to 30 mph in the afternoon. 15 to 20 mph with gusts to 30 mph. 10 to 15 mph. Gusts up to 30 mph.
Expected snowfall: Locally up to 1 in. Little to no accumulation. in. 0 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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