Eastern Sierra Avalanche Forecast - 2/6/14

Our goals are lofty, but our ask is simple... We need your help... Click Here to Find Out How

THIS AVALANCHE ADVISORY EXPIRED ON February 7, 2014 @ 8:22 pm
Avalanche Advisory published on February 6, 2014 @ 8:22 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger this morning is generally LOW with ares of MODERATE danger on steep north facing slopes due to buried persistent weak layers at the bottom of the snowpack. A winter storm with extended periods of dense snow, very strong southwest winds and gradually warming temperatures will load existing weak layers and last week's snow.

DANGEROUS AVALANCHE CONDITIONS WILL DEVELOP TONIGHT AND CONTINUE THROUGH SUNDAY

How to read the advisory


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

Bottom Line

The avalanche danger this morning is generally LOW with ares of MODERATE danger on steep north facing slopes due to buried persistent weak layers at the bottom of the snowpack. A winter storm with extended periods of dense snow, very strong southwest winds and gradually warming temperatures will load existing weak layers and last week's snow.

DANGEROUS AVALANCHE CONDITIONS WILL DEVELOP TONIGHT AND CONTINUE THROUGH SUNDAY

  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Persistent Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Increasing Danger

The persistent avalanche problem is the current problem this morning. This layer deserves our attention as the storm comes in with cold temperatures then changing over to warm wet dense snow that will be measured in feet this time. If the storm comes in as forecasted, expect these layers to react to heavy loading. 

Avalanche Problem 2: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Trend ?
    Increasing Danger

Strong west and southwest winds will be moving alot of new snow onto north and east slopes at high elevations beginning tonight when the brunt of the first storm reaches the area.  This is a real Sierra storm and wind loading will become the primary avalanche problem over the weekend. Heavy 12-18% density snow will form slabs that will break within the storm snow or on the snow that fell last week. If loading rates are really high, storm slab avalanches could release on the buried facets and depth hoar, causing large avalanches during the storm.

advisory discussion

The tropics pay a visit to the eastern Sierra this weekend. After a week of below normal temperatures and 12-16” of snow a week ago, a warm storm with high snow levels could dump a couple of feet of snow above 8,000 ft.   Sustained wind speeds of 60 mph gusting to 100 mph are in store for the Sierra Crest. Unfortunately snow lines will be high after an initial shot of cold air brings 4-8” of snow today. Snowlines then rise to 8,000 ft. - right between the Town of Mammoth and Tamarack Lodge. Some locations are going to get a lot of water out of this storm. The weight of this snow is going to stress the snowpack and make for a wild ride in terms of backcountry avalanche hazard.

The persistent avalanche problem is the current problem this morning. December and January’s weather patterns created highly variable snow conditions and last week’s storm buried 2 to 10 inches of large weak facets and depth hoar under 12-16” of new snow. Some people skied and disregarded the multiple faceted layers, others carefully evaluated slopes because buried weak faceted snow has a nasty habit of producing avalanches on some slopes and not on others.

This layer deserves our attention as the storm comes in with cold temperatures then changing over to warm wet dense snow that will be measured in feet this time. If the storm comes in as forecasted, expect these layers to react to heavy loading Saturday and Sunday. While there was not enough of a new snow load to cause a natural avalanche cycle last week, this storm will load the snowpack in a meaningful way.

 

 

recent observations

Snowpits in Rock Creek at the 9,300 to 9700 ft elevation were similar- 6-8 inches of storm snow over a stout 1 inch thick melt freeze crust. Large depth hoar and solid facets formed a 4-8 inch base layer on the ground. Stability tests did not break through the crust. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 16 deg. F.
Average wind direction during the last 24 hours: wsw
Average wind speed during the last 24 hours: 50 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: 2 inches
Total snow depth: 26 inches
weather

A rare phenomena called a winter storm with bring severl feet of snow to the area over the next few days. The warm moisture source will bring rain to the 7.000 to 8,000 ft elevations. Strong to very strong west and southwest winds will howl over the ridges with gusts exceeding 100 mph. Daytime temperatures will be about 10 degrees warmer than earlier this week with mild night time lows in the mid 20's and low 30's.  Heavy rain and snow will begin inearnest this afternoon and evening and continue through Sunday. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: clouds, rain and snow snow snow
Temperatures: 30-40 deg. F. 20-30 deg. F. 25-35 deg. F.
Wind direction: SW SW SW
Wind speed: 23-30 25-40 20-35
Expected snowfall: 4-6 in. 6-12 in. 6-12 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: cloudy, snow snow snow
Temperatures: 20-30 deg. F. 14-25 deg. F. 20-30 deg. F.
Wind direction: W w w
Wind speed: 55-75 55-75 50-70
Expected snowfall: 4 in. 8-14 in. 8-16 in.
Disclaimer

ESAC receives support from ...