Eastern Sierra Avalanche Forecast - 2/25/14

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THIS AVALANCHE ADVISORY EXPIRED ON February 26, 2014 @ 10:31 pm
Avalanche Advisory published on February 25, 2014 @ 10:31 pm
Issued by Sue Burak - Inyo National Forest
bottom line

The avalanche danger is LOW this morning but will increase as the first of two storms impacts the Mammoth area. Expect the avalanche danger to increase to CONSIDERABLE or HIGH by Thursday. Over 20 inches of snow above 9,000 ft will accumulate later today and tonight. With a second storm dropping another 18-20" Friday into Saturday, I expect dangerous avalanche conditions to exist in the Mammoth Lakes Basin this weekend.  This danger rating is for the Mammoth Lakes Basin. 

This advisory is for Wednesday, February 26, 2014. 

How to read the advisory


  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Bottom Line

The avalanche danger is LOW this morning but will increase as the first of two storms impacts the Mammoth area. Expect the avalanche danger to increase to CONSIDERABLE or HIGH by Thursday. Over 20 inches of snow above 9,000 ft will accumulate later today and tonight. With a second storm dropping another 18-20" Friday into Saturday, I expect dangerous avalanche conditions to exist in the Mammoth Lakes Basin this weekend.  This danger rating is for the Mammoth Lakes Basin. 

This advisory is for Wednesday, February 26, 2014. 

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Storm Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

Even though the avalanche danger this morning is LOW, expect the overall stability to deteriorate as the storm moves in and snow begins to accumulate. Strong southwest winds will form widespread areas of wind drifts and slabs that will be sensitive to skier triggering. 

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

Snowpacks in Rock Creek have the weakest snow compared to the Mammoth Basin. Snowpack depths are less than 2 ft up to around 9,700 ft. Higher terrain has about 3 ft. of snow but skiing is limited to the summer trails, meadows and gentle slopes in glades.  The depth hoar facets are the base of the Rock Creek snowpack and continue to react in stability tests. 

The persistent buried weak layer is widespread in the Mammoth Basin and ranges in thickness from around 6" to over 2 ft. A strong cohesive slab lies on top of the weak layer. Stability tests done within the last 5 days are not showing instability on this layer but it may be dormant and needs only some loading from the next two storms to wake up and become active. Look out for whumpfing and slope settlement the next few days. It may be difficult to know if whumpfing is confined to storm snow or deep buried snow but as always, whumpfing is a red flag and warns of unstable snow. 

advisory discussion

The long awaited real deal, genuine, bona fide winter storm is almost here. Winter has returned and most of us are accustomed to mild weather and generally stable snowpacks. The next few days brings welcome snow and many more areas will now be open for skiing and riding.

Refresh your companion rescue skills and head to the Beacon Basin this morning.  New snow measured in feet, sustained winds and the prospect of powder skiing are the perfect recipe for trouble if you let the lure of untracked snow override common sense. Stick to lower angle terrain in the trees during the storm and avoid wind loaded slopes. 

In addition to the obvious avalanche problem of storm slabs and direct action avalanches, facets under a series of crusts in the upper 6- to 8 inches of the snowpack in the Mammoth Basin are a potential weak layer.  Widespread near surface facets at high exposed elevations may be blown away by storm winds but may survive in glades and sheltered areas. Recently formed wind drifts sitting up on near surface facets will likely be sensitive to the weight of a skier or rider by tomorrow morning. 

Overall, snowpack conditions are quite different between mid and high elevations. Although temperatures have been relatively warm at 8,500 to 9,500 ft breezes and the large areas above treeline on shaded north aspects have kept the snow dry and cool. Mid elevation snowpacks are melting on the surface and the series of crusts formed over the past 5 days all have facets under the crusts and are reactive in stability tests. 

 

recent observations

An avalanche course in the Rock Creek drainage provided two days of stability test results and snowpack observations. The depth hoar layer is still active with propagation and collapse on the depth hoar on the ground. Some instability observed in the upper 10 cm, similar to the upper snowpack in the Mammoth Basin. Small facets under a series of crusts are the weak layer in many ECT's and CT's and are layers of concern during the upcoming heavy loading. 

Near surface faceting is widespread in the Rock Creek and Mammoth basins. Large, cupped near surface facets are widespread in Rock Creek and smaller facets have been reported from the Lakes Basin. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 31 deg. F.
Max. temperature in the last 24 hours: 48 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 25 mph
Maximum wind gust in the last 24 hours: 30 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 38 inches
weather

Two major winter storms will impact the area beginning this afternoon. First system will arrive this afternoon and by Thursday morning, over 20 inches of snow is expected above 9,000 ft. A winter weather advisory begins this afternoon at 4 PM and continues until 10 AM Thursday morning. The first storm could bring 8-10 inches of snow to the town of Mammoth by tomorrow morning with up to 2 feet expected at the higher elevations. The Friday/Saturday storm is expected to bring 15" of snow to the town and at least 2 ft. 3 feet to the higher elevations. Strong southwest winds gusting 60 to 80 mph over the high ridgetops are expected through Thursday and again for the Friday/Saturday storm. 

Daytime highs will cool off from the upper 40' and low 50's at the 8,000 to 10,000 ft elevations. Higher elevations will cool down to the low 30's. Snowlines will be around 7,000 ft and little, if any, rain is expected. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Tuesday Tuesday Night Wednesday
Weather: clouds clouds, snow clouds, snow
Temperatures: 40-48 deg. F. 18-25 deg. F. 33-41 deg. F.
Wind direction: SW S SW
Wind speed: 10-15 25-30 25-30
Expected snowfall: 1-2 in. 15 in. 6 in.
Over 10,000 ft.
  Tuesday Tuesday Night Wednesday
Weather: clouds clouds clouds
Temperatures: 31-39 deg. F. 14-20 deg. F. 24-32 deg. F.
Wind direction: SW SW SW
Wind speed: 10-15 35-45 40-50
Expected snowfall: 1-2 in. 15 in. 6-9 in.
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