MODERATE avalanche danger is increasing towards CONSIDERABLE avalanche danger at all elevations as rain and wet snow continue. Loose wet, persistent slab, and wind slab avalanche problems are a concern over the next 24 hours.
Loose wet avalanche activity was reported yesterday and will continue to be a problem with additional rain and wet snow accumulation. Snow covered NW-N-NE aspects at any elevation are the likely location for this avalanche problem to occur. Loose wet avalanches are possible in isolated areas on all other aspects. Avalanche size up to D2 is possible.
Rain and wet snow continue to add load to areas of slab over weak faceted snow on NW-N-NE aspects both above and below treeline. Above treeline areas have hard slabs while near to below treeline areas hold soft slabs. Recent field observations have regularly indicated isolated areas of persistent slab instability. A race is on to see if loading brings the facets to a point of failure before increasing moisture from rain and wet snow affects the moisture content and changes the characteristics of the facet layer.
Quick hand pits will remain effective for identifying slab over weak, loose grain (sugary) faceted snow until significant new snowfall occurs. Keep in mind that this problem exists in isolated areas so investigate the snowpack structure frequently as you cover terrain. This problem may exist only in the mid to lower portion of avalanche start zones. Avoid steeper slopes in areas where snow surface cracking, whumpfing, and/or unstable snowpit test results are occurring. Small avalanches can have increased consequences right now given the prevalence of rocks and trees.
Development of a wind slab avalanche problem tonight will be directly related to snow level and new snow accumulation. If snow levels are at the lower end of forecast elevation and snowfall amounts push the upper end of forecast possibility, wind slabs will form tonight. Near and above treeline areas on NW-N-NE-E aspects above 8,000' will be most problematic.
Look for and avoid areas of drifting snow, especially along ridgelines where cornices and/or wind pillows have formed.
* Loose wet avalanche activity occurred yesterday in the Mount Rose area on steep northerly aspect terrain in the 8,600' to 9,200' elevation range. Avalanche size was large enough to injure a person.
* The recent rain, wet snow, and high humidity has added significant moisture to areas that held faceted snow on the surface with no overlying slab. Where faceted snow exists under a slab, the facets have thus far remained dry.
* Observations from around the forecast area this past week have shown isolated areas of unstable persistent slabs (slab over faceted snow) on NW-N-NE aspects, especially near and below treeline.
* NW-N-NE aspects above 8,000' in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay. Areas of decent coverage exists above 8,500' on NW-N-NE aspects in the Carson Pass area. Coverage decreases on all other aspects. Large areas of bare ground exist on the vast majority of southerly aspects at all elevations.
