Avalanche Advisory: Monday - Feb 5, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON February 6, 2018 @ 6:39 am
Avalanche Advisory published on February 5, 2018 @ 6:39 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Avalanche danger is rated LOW today.  Continued unseasonably very warm temperatures, light winds, and clear skies will make it possible for small loose wet avalanches to occur today in isolated areas on E to S to W facing slopes as they warm from sun exposure.  Firm snow surfaces and obstacles due to the thin snowpack are more of a concern than avalanches at the moment. 

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
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    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
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    Very Large
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    Small

Unseasonably very warm temperatures, light winds, and clear skies will make it possible for small loose wet avalanches to occur today in isolated areas on E to S to W facing slopes as they warm from sun exposure.  If winds and clouds increase this afternoon, this melting will lessen, especially for more westerly facing slopes.  Loose wet slides are most likely to originate naturally near rock-bands on slopes steeper than 35 degrees, as they heat up from sun exposure and warm up the nearby snow.  Human triggers could also occur as wetness deepens through the snowpack and ski/board penetration becomes deep, and a turn pushes enough snow down slope that could entrain more snow.  While this loose wet snow movement is not likely to be big enough to bury a person, the heavy thick nature of such a slide could drag a person off their feet.  Time it so that you are on steep slopes when they are soft enough for fun turns, and off of them before they become saturated, unsupportable and potentially unstable.  This problem is even more limited due to the very thin snowpack that exists on southerly facing slopes, and the fact that many of these slopes are even without snow all together.

advisory discussion

A week and a half has gone by now since we have had any notable snow deposition from either snowfall or wind transport, and almost as many days of well-above average temperatures.  Despite barely freezing temperatures at night, clear skies have continued to lead to solid re-freezes of most slopes.  Sun exposure during the day will start the melt part of the cycle all over again progressing from E thru S thru W facing slopes at all elevations, and north facing slopes at lower elevations and up to ~9,700’ where slopes are treed.  The only thing different about this early February snowpack warming and the warming that occurs in April is the still-relatively low sun angle in the sky, keeping the intensity of the sun less, and therefore slope warming less.  If we had the same temperatures, winds, and cloud cover in April as we do now, we would expect to see quite a bit more loose-wet activity, and the danger of larger and more numerous slides would be greater.  Still, isolated loose-wet activity is possible, and this should be kept in consideration especially if riding in areas where a small slide could result in a fall in dangerous terrain.  Keep in mind that before these E-S-W facing slopes get exposed to the sun, they are likely to be very firm and icy, and a fall could lead to a slide for life.  Crampons and an ice ax would be wise if it is possible that you might be traveling on these steep slopes before they soften.  Also note that these slopes begin to re-freeze quickly, and start to become crunchy as the sun-angle becomes less direct on them, especially at upper elevations.  For example, a SE slope at 1pm which still appears to have full sunshine on it, will have started to refreeze already because the sunshine angle on the slope has decreased enough.   

This extended period of high-pressure ridging, dry conditions, and warm temperatures continue to melt away our already thin snowpack especially at lower elevations and on E-S-W facing slopes.  

Persistent loose sugary snow is still being found mid-snowpack in many areas on NE-N-NW aspects due to the thin snowpack.  There have been no reports of any avalanche activity on these layers yet this season.  But the weak structure is still important to note, for if we ever get a big heavy dump this season, we wouldn't be surprised to see some larger than expected avalanches failing in these deeper layers.  

Lastly, thin snowpack in many areas are hiding rocks, logs, and other obstacles just below the surface.  Last week a skier hit a shallow rock just below the surface that he didn’t see skiing out of the negatives, resulting in a fall into other just barely covered rocks, and a broken clavicle. 

Weather and CURRENT CONDITIONS
weather summary

For today well above average seasonal temperatures are expected with highs in the upper 40’s around 10,000’, light NW winds, and sunny skies.  Winds and clouds are expected to increase a bit at upper elevations this afternoon as the result of a storm pushing thru the Northwest.

Models continue to stay in agreement that high pressure, dry conditions, and well above average temperatures will be with us thru next week, and who knows how much longer past that. 

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: Sunny then becoming partly cloudy Clear Sunny
Temperatures: 52 to 58 deg. F. 26 to 31 deg. F. 47 to 53 deg. F.
Mid Slope Winds: Northwest Northwest Northwest
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Sunny Clear Sunny
Temperatures: 45 to 50 deg. F. 24 to 29 deg. F. 42 to 47 deg. F.
Ridge Top Winds: Northwest Northwest Northwest
Expected snowfall: 0 in. 0 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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