Eastern Sierra Avalanche Advisory

Avalanche Advisory published on April 13, 2014 @ 7:05am: Issued by Sue Burak - Inyo National Forest
This advisory is valid for 24 hours.
bottom line

The overall avalanche danger is MODERATE today. Wet avalanches are possible in steep, sunny, alpine terrain when today's sunshine softens and melts the snow surface. Small cornices may be sensitive to your weight along upper elevation ridgelines

How to read the advisory


Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.

avalanche danger

How to read the advisory

2. Moderate

Above treeline

1. Low

Near treeline

No Rating

Below treeline

The overall avalanche danger is MODERATE today. Wet avalanches are possible in steep, sunny, alpine terrain when today's sunshine softens and melts the snow surface. Small cornices may be sensitive to your weight along upper elevation ridgelines

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.

weather

Morning temperatures are running 5 to 10 degrees colder this morning than yesterday.

North winds are gusting 35-45 along the ridgetops. Daytime highs will be in the upper 40’s today above 10,000 ft.; mid elevations will cool off from yesterday’s 55-60 degrees to the upper 40’s and low 50’s. The next few days will be dry with nights below freezing at the higher elevations. 

recent observations

Small to long running, 1,000 ft. wet slides released yesterday on east and northeast facing slopes in alpine terrain in Rock Creek, Mammoth and the backcountry west of June Lk.

A snowpit dug at 12,000 ft in the Rock Creek area is shown below. The snowpack is close to 5 ft deep- much deeper than the 3 ft snowpack at 10,000 ft. There are multiple facet/crust combinations. Fine grained rounds predominate in the upper half of the pack probably from the early March and end of March storms. The good ol’ Rock Creek depth hoar is  there and is 12 inches thick. The crusts had facets under the crusts and ice masses ( flow fingers) in the snow closest to the surface. 

Avalanche Problem 1
type aspect/elevation characteristics
likelihood size trend
likely
unlikely
large
small
Same Danger
description

Despite thick clouds and cooler temperatures yesterday, there was another cycle of small to large loose wet snow avalanches. Yesterday was also the fourth and fifth day that nights were above freezing so there was a lot of water percolating through the snowpack.

With a clear night last night and solid freeze, the snow will take a little longer to reach the magic 0C point when the snow begins to melt at the surface. Wet snow fails due to a rapid decreases in strength compared to dry snow that fails in response to a load. Watch out for wet loose snow slides starting above you when traveling below cliffs, along valley bottoms with steep slopes overheard. These places are often terrain traps. Ascending slopes to ski a couloir exposes you to wet loose slides starting above you. Get an early start and get off the snow before it turns to a soggy unsupportable mess. 

Avalanche Problem 2
type aspect/elevation characteristics
likelihood size trend
likely
unlikely
large
small
Decreasing Danger
description

The buried depth hoar layer is a problem at the higher elevations in Rock Creek. The depth hoar is slowly gaining strength but water percolating through the snowpack has not reached the layer. Depth hoar rapidly loses strength when exposed to water but wet snow avalanches are a result of interactions between the snow surface, snowpack structure and the amount of energy at the surface and within the snowpack. 

The poor structure is widespread above 10,000 ft on north and east facing slopes. If your skis break through to the ground, you know it's time to find another aspect -even a small change in slope aspect may alleviate the problem. 


ESAC Weather Page

Weather Station Links:
June Mountain Summit
Mammoth Summit
Rock Creek
CURRENT CONDITIONS  Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 29 deg. F.
Max. temperature in the last 24 hours: 52 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 20-30 mph
Maximum wind gust in the last 24 hours: 45 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 34 inches
Two-Day Mountain Weather Forecast  Produced in partnership with the Reno NWS
For 8,000 to 10,000 ft.
  Sunday Sunday Night Monday
Weather: sunny clear sunny
Temperatures: 45-50 deg. F. 30 deg. F. 50 deg. F.
Wind direction: N N East
Wind speed: 15-25 15-20 5-10
Expected snowfall: 0 in. 0 in. 0 in.
For above 10,000 ft.
  Sunday Sunday Night Monday
Weather: windy clear, north winds sunny
Temperatures: 36-44 deg. F. 28-31 deg. F. 50 deg. F.
Wind direction: North north South
Wind speed: 15-25 15-20 5-15
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory only describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.



ESAC receives support from ...