Avalanche Advisory: Tuesday - Feb 6, 2018

 
 
 
 
 
-- placeholder --
 
 
 
THIS AVALANCHE ADVISORY EXPIRED ON February 7, 2018 @ 6:30 am
Avalanche Advisory published on February 6, 2018 @ 6:30 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Loose wet avalanches will be possible today on E to S to W facing slopes as the sun moves across the sky. You can avoid the problem by getting off of steep solar aspects by the time they are soft enough that you can sink into wet snow deeper than your boot tops, or before large rollerballs are running down the hill around you. Early morning icy conditions that could result is a slide for life situation, and hidden obstacles under the thin snowpack pose additional hazards today.

1. Low

?

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

1. Low

?

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

1. Low

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Temperatures more typical of early April will continue today, and clear skies will allow plenty of solar radiation to heat E to S to W facing slopes as the sun moves across the sky. The February sun is not as intense as it would be in April, and so “spring-like” thawing will not be as extreme as actual spring conditions. A general lack of snow coverage on solar aspects means that the distribution of potential point releases will be isolated to those features that have been able to retain snow, like gullies and high elevation bowls. But that doesn’t mean natural loose wet avalanches will be impossible today on rocky, sunny slopes steeper than about 35 degrees. Look for rollerballs coming down the slope around you. Human triggered loose wet avalanches will be possible on slopes that become deeply saturated with free water by late morning and through the afternoon. Sinking into wet snow to your boot top is a good indicator of these unstable conditions. Timing your descent so that you are out of steep sunny terrain before deep thawing can occur is the best strategy for avoiding loose wet avalanches.

advisory discussion

The last time we saw loading from new snow in the Sierra was on January 27th when northerly winds redistributed cold snow from the previous storm. Since then, another ridge of high pressure has settled over the west coast and well-above average temperatures have been the new normal. Clear skies and below freezing temperatures overnight have allowed the snowpack to get a good re-freeze in most areas. But as the sun again heats E to S to W facing slopes today, with few clouds impeding the incoming radiation, the thawing process will begin all over again. Even lower elevation northerly slopes have developed melt-freeze crusts where vegetation has helped hold in the heat. A few small loose wet avalanches have been reported on steep Southeasterly slopes. All of this has occurred despite the relatively low angle of the February sun. That low sun angle means snow surface warming will be less than we would expect to see in April or May. And our thin to non-existent snowpack on the slopes receiving the most warming will further isolate the avalanche problem. That doesn’t mean that loose wet avalanches will be impossible as the snow becomes deeply saturated with melt water by late morning. Even small and slow-moving loose wet avalanches can be dangerous in or above terrain traps like cliffs or extreme terrain. They could knock you off your feet and take you somewhere you don’t want to be. Avoiding slopes that are warm enough for large rollerballs or to sink in past your boot tops is the best way to keep yourself out of trouble.

Early in the day, before the snow softens, icy conditions will be a hazard. Crampons could help reduce your exposure in steep terrain where falling could result in a slide for life. The thin snowpack also means barely covered obstacles like rocks and logs will become more and more a problem as slopes melt out. Hidden obstacles resulted in a broken clavicle for one skier in the Negatives recently.

On northerly slopes, sugary facet snow still exists in layers throughout the snowpack. These layers are inherently weak and are worth monitoring even though an avalanche failing on them is unlikely. If we do ever get a good dump this season these weaker layers will suddenly become very concerning.

 

Weather and CURRENT CONDITIONS
weather summary

Spring-like conditions will continue today with high temperatures more typical of early April. Breezy northerly winds across the ridgetops will subside by the afternoon with light breezes expected through the rest of the week.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny. Clear. Sunny.
Temperatures: 45 to 51 deg. F. 27 to 32 deg. F. 47 to 55 deg. F.
Wind Direction: NW Light winds. Light winds.
Wind Speed: around 10 mph. Light winds. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny. Clear. Sunny.
Temperatures: 38 to 44 deg. F. 25 to 31 deg. F. 40 to 46 deg. F.
Wind Direction: N NE Light winds.
Wind Speed: 10 to 15 mph with gusts to 30 mph. 10 to 15 mph in the evening becoming light. Light winds.
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.

ESAC receives support from ...