Eastern Sierra Avalanche Advisory

Avalanches don't forgive people for not knowing!  Come join the Eastern Sierra Avalanche Center forecasters presenting an Introduction to avalanche safety and backcountry travel, avalanche accidents in the Sierra with some personal accounts discussing factors effecting human decision... more
Avalanche Advisory published on January 20, 2018 @ 6:50 am
This Avalanche Advisory expires in 8 hours, 0 minutes
This advisory is valid for 24 hours
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

The overall avalanche danger is MODERATE today at upper elevations. Light to moderate NW winds may create isolated new wind slabs with all of that light new snow available for transport. Steep, leeward slopes where the most new snow accumulated yesterday will be the most suspect. Watch for blowing snow, slopes with newly formed cornices up top, and rounded drifts as areas to avoid. Below treeline avalanches will be less likely, and below ~9,000’, the new snow is not enough to completely cover rocks and brush and avalanches are unlikely.

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

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.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

New snow from yesterday and this morning has proven to be largely unconsolidated and loose. Several small sloughs were observed on steep northerly slopes yesterday in the Mammoth and Virginia Lakes areas. Windward slopes are primed with light snow available for wind transport and as light to moderate NW winds blow throughout today, isolated new wind slabs may form at upper elevations. Take special notice where the most snow accumulated yesterday, primarily in the northern third of the forecast zone. More loose snow means winds could create large slabs. You are most likely to encounter wind slabs today on steep upper elevation slopes and on the leeward sides of ridges, under cornices, and the sidewalls cross-loaded gullies.

advisory discussion

SW winds preceded the cold low pressure system that passed through yesterday morning, but most of the snow fell during calmer conditions. Ski cuts, test slopes, and snowpack tests throughout the Mammoth Zone and up in Virginia Lakes show the new snow to be well bonded and largely unconsolidated. Several small sloughs were observed on steep northerly slopes. With cold temperatures, light winds, and a few showers overnight and this morning, windward areas are flush with light new snow ready for transport. Light to moderate winds today, primarily from the N and NW, could create small wind slabs in isolated areas that promote drifting. Be careful in steep alpine terrain. Watch for blowing snow, cornice formation, and rounded drifts will be the best clues for wind slab formation.

High humidity and warm temperatures has caused the upper snowpack to set up into a hard layer above the persistent weak layer. Probing and digging has shown that this sugary snow still exists in the middle and bottom of the snowpack in specific areas, but test results have been less and less reactive. We will have to monitor it and see what stress it can handle before any major new loading.

Below ~9,000’ the new snow will not be enough to cover the rocks and brush poking up from the surface.

 

Weather and CURRENT CONDITIONS
weather summary

Dry and cool conditions will prevail this weekend as weak high pressure moves over the region. Temperatures will be cooler with daytime highs in the lower-mid 30s in lower elevations and teens to 20s near the Sierra Crest. Lows tonight will drop off to the teens to single digits for most areas.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Today Tonight Sunday
Weather: Mostly cloudy then becoming sunny. Isolated snow showers in the morning. Clear then becoming partly cloudy. Partly cloudy then becoming mostly cloudy.
Temperatures: 22 to 28 deg. F. 10 to 16 deg. F. 29 to 35 deg. F.
Wind Direction: N NW Light winds.
Wind Speed: 10 to 15 mph with gusts to 30 mph. 10 to 15 mph with gusts to 30 mph in the evening becoming light. Light winds. Gusts up to 25 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Today Tonight Sunday
Weather: Mostly cloudy then becoming sunny. Isolated snow showers in the morning. Partly cloudy. Partly cloudy then becoming mostly cloudy.
Temperatures: 15 to 21 deg. F. 5 to 10 deg. F. 22 to 28 deg. F.
Wind Direction: N NW W
Wind Speed: 15 to 20 mph with gusts to 40 mph. 10 to 15 mph. Gusts up to 35 mph decreasing to 25 mph after midnight. 10 to 15 mph. Gusts up to 25 mph in the afternoon.
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 ...