Spring Statement

[Brandon]

This advisory was posted on Friday, April 27th, 2007 at 4:28 pm and covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Sonora Pass on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

Avalanches will continue to occur this spring, but it is time to close the avalanche center. Thank you all of the groups and individuals who made generous donations to the Sierra Avalanche Center this winter. Our corporate sponsors, the general public who made cash donations and purchased Ski for SAC day tickets, as well as everyone who submitted snowpack, weather, and avalanche observations made our avalanche advisory products possible during the 2006-2007 winter season. Here are a few notes on spring snowpack and avalanche conditions.

There are three major avalanche concerns to watch for during the remainder of this spring and into early summer. The first is near surface wet snow avalanche activity. Be aware of the depth of wet snow in the area where you are traveling. If you sink into wet snow up to the tops of your boots, it is time to get to terrain less than 25 degrees in slope angle that does not have steeper terrain above it. Get off of your equipment on a regular basis to check boot penetration depth.

You can use the Snotel (CA and NV) and National Weather Service sites to monitor hourly temperatures at many points throughout the forecast area. If overnight refreezing conditions of the snowpack return, getting out early and finishing in time to have a lunchtime barbeque should be your goal. Start with east aspects and the follow the sun to south and then to west aspects. Call it a day when signs of wet snow instability such as boot top height penetration, significant roller ball activity, or any wet snow avalanche results from small test slopes are observed. As a matter of etiquette, do not leave deep ruts in a slope that will freeze overnight and ruin the slope for others the next morning.

The second major concern is naturally occurring deep wet slab avalanches in isolated areas. Higher elevation northerly aspects where dry basal layer facets exist within the snowpack structure are suspect. This snowpack structure has been observed in the Carson Range (Mount Rose area) and may exist elsewhere. In this area, free water did not percolate to the depth of the faceted basal layer on northerly aspects during the warm periods of March. With high late spring sun angles and warm air temperatures, free water percolation to the basal snow layer depth is possible. This is the typical snowpack structure and weather event that causes deep wet snow instability. These events are very difficult to predict and can result in large, destructive avalanches.

The third major concern involves avalanche activity that will likely occur during and after any late season storms. Expect a period of snowpack instability during the storm itself, then a second cycle of avalanche activity as rapid warming occurs post storm. New snow will likely fail at the base of the storm snow where there is a significant density difference between the old and new snow. During the storm, watch for the typical signs of mid winter instability such as recent avalanche activity, wind loading, collapse, audible whumphing sounds, and/or shooting cracks. Post storm, watch for the signs of wet snow instability outlined above.

Other hazards such as cornice collapse, moats, glide cracks, and open creeks exist. Stay well back from abrupt edges along ridgelines as human triggered cornice collapse will remain possible for some time to come. Stay out from under cornice areas as well, especially if you can see water dripping from the cornice as this is an obvious sign of instability. Areas of weak snow around rocks, vegetation, and along the base of cliff bands exist. Move carefully around these features as the snow could collapse under your body weight allowing you to fall into a melted out hole next to the feature. Exercise caution when traveling near or attempting to cross creeks as wet snow along the banks can easily collapse under the weight of a person. You really don’t want to get that wet just yet.

As the season begins to change again and the days become shorter, check back on our home page for early season fundraising events for the 2007-2008 season. Enjoy your spring and summer and we will see you next fall.

Brandon Schwartz and Andy Anderson, Avalanche Forecasters

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Today's Central Sierra Weather Observations: check Snotel (CA and NV) and NWS remote sensors
0600 temperature at Sierra Crest (8,700 feet): no data deg. F
Max. temperature at Sierra Crest past 24 hours: no data deg. F
Average wind direction at Sierra Crest past 24 hours: no data
Average wind speed at Sierra Crest past 24 hours: no data mph
Maximum wind gust at Sierra Crest past 24 hours: no data mph
New snow fall at 8,200 feet past 24 hours: no data inches
Total snow depth at 8,200 feet: no data inches

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Mountain Weather Forecast For Today:
Check the NOAA Website for current weather forecasts.
Temperature forecast for 8,000 to 9,000 feet: no data degrees F.
Ridgetop winds forecast for the Sierra Crest: no data
Snowfall expected in the next 24 hours: no data inches

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2 Day Mountain Weather Forecast:
7000 to 8000 Feet:
no data

Above 8000 Feet:
no data