Eastern Sierra Avalanche Advisory - 3/17/17

Avalanche Advisory published on March 17, 2017 @ 6:25 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Spring conditions continue.  As slopes warm throughout the day, starting with east-facing, then south, then west, natural and human triggered small loose wet avalanches will become increasingly possible.  Timing of these avalanches will also depend on elevation, winds, and cloud cover.  Even small wet slides are heavy and dense and could carry a rider into undesirable terrain or entrain enough snow to bury a person.  Start early and be off steep slopes before they become saturated and unsupportable.  Avoid being under or on top of cornices that could fail, and beware of very firm conditions before slopes soften that could result in a slide-for life even on less steep slopes.  Evaluate snow and terrain carefully. 

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Below Treeline
Avalanche Problem 1: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

As slopes warm, soften, and become wet throughout the day, natural and human triggered small loose wet avalanches will become increasingly possible.  Forecasted partly cloudy skies and moderate SW winds today could slow and lessen the extent of this warming, especially at mid and upper elevations.  Clear skies led to snow-surface re-freeze last night, but warm air temps likely reduced the thickness of the re-freeze, and slopes will go from firm to soft and potentially unsupportable quicker.  This was observed yesterday morning in the convict area by multiple parties skiing easterly facing slopes that softened quickly.  East facing slopes will soften first in the morning, followed by south, then west in the afternoon, and this softening will be intensified near cliffs and rock outcrops.  Pay attention to signs such as large pinwheels and sinking past your boot top as indicators of slopes becoming unstable, and that steep terrain on these aspects should be avoided.   

The timing and amount slopes soften depends on multiple factors:  Aspect as it relates to sun exposure (Easterly facing slopes will warm first in the morning, followed by south and then west in the afternoon); Elevation: lower elevations will warm more quickly earlier in the day than higher elevation, even on non-solar northerly aspects; Cloud cover: clouds blocking the sun will keep slopes harder and firmer longer, but they also act to keep heat in and reduce how hard and thick slopes refreeze at night and result in more warming of more northerly facing slopes that would otherwise stay cold under clear skies; Air temperature: Warmer air temperatures will lead to more slope warming.   


advisory discussion

The last snowfall we received was almost 2 weeks ago on March 5th, and since then spring conditions have dominated our area with above average temperatures and lots of sunshine.  Loose-wet avalanches have been and will continue to be the main, if not only, avalanche concern for a few more days until the weather changes and the next winter storm impacts our area early next week.  The past two weeks have been a big window of opportunity for many to explore the high alpine peaks and hunt for some good corn skiing if one times aspect and elevation and right.  This hasn’t been always easy with the variable cloud cover and winds which we have been receiving which effect how the snow softens.  In terms of mountain hazards, very firm conditions have been an even greater concern than avalanches lately.  The last snowfall almost 2 weeks ago was accompanied by very high winds, and much of the alpine was left highly wind-effected and firm.  Frozen slopes before they soften and areas with hard smooth wind board threaten slide-for-life conditions.  Crampons, ice axes, whippets, and most importantly good judgement, are all essential for venturing into the alpine.  Warm days and softening snow also leads to greater threat for cornice failures, either naturally or from someone's weight ontop of one.  Pay close attention if you are travelling along ridgelines to give edges of slopes that could be corniced a wide berth, and avoid being under cornices especially as the day warms.     

recent observations

-3/16 - Bishop - Mt Tom: Clouds, Easterly slopes softening

-3/15 - Bishop - Mt Tom: Slope softening and conditions

-3/15 - Pine Creek - SE Couloir: Snow softening and conditions

A skier skiing a steep couloir off of North Palisade peak this past week had a dynafit binding pre-release resulting in him cartwheeling down through rocks.  Incredibly luckily, he only sustained bruises and no major injury.    

weather summary

Today (Friday) high pressure continues with above average temperatures into the upper 40s around 10,000’, partly cloudy skies and moderate southwest winds gusting up to 50mph above 10,000’. 

For tomorrow (Saturday), a weak disturbance will affect our area, bringing slightly gustier winds with gusts up to 80mph aboev 10,000', mostly cloudy skies by afternoon, and a chance of scattered snow showers with little accumulation expected.  Temperatures will remain warm.    

Long Term:  Our spring conditions look to be ending as a more active weather pattern moves in early next week bringing cooler temperatures and several waves of snow showers beginning on Tuesday thru the end on the week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy Mostly cloudy then becoming partly cloudy. Mostly cloudy. Slight chance of showers in the afternoon.
Temperatures: 48 to 58 deg. F. 31 to 37 deg. F. 47 to 55 deg. F.
Mid Slope Winds: SW SW SW
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Partly cloudy Partly cloudy Partly cloudy then becoming mostly cloudy. Chance of snow showers in the afternoon.
Temperatures: 41 to 47 deg. F. 26 to 32 deg. F. 40 to 48 deg. F.
Ridge Top Winds: SW SW SW
Expected snowfall: 0 in. 0 in. 0 in.
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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