Eastern Sierra Avalanche Forecast - 3/16/14

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THIS AVALANCHE ADVISORY EXPIRED ON March 17, 2014 @ 7:05 am
Avalanche Advisory published on March 16, 2014 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
bottom line

The overall avalanche danger is generally LOW for the Mammoth Basin, Rock Creek and June Mountain areas. Cold overnight temperatures have allowed another solid refreeze of the snow surface at alpine and mid elevations in the trees. Wet loose snow activity will be limited in alpine zones but the snow surface is likely to thaw by this afternoon on mid elevation slopes that receive direct sun.  Small isolated areas of loose wet snow instability could occur today on sunbaked slopes in alpine areas and in the trees around rock outcrops and ribs.

The avalanche rose is filled out for alpine (above treeline) and mid elevations in the trees. Areas that are gray do not have snow or there is no snowpack information.

How to read the advisory


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

Bottom Line

The overall avalanche danger is generally LOW for the Mammoth Basin, Rock Creek and June Mountain areas. Cold overnight temperatures have allowed another solid refreeze of the snow surface at alpine and mid elevations in the trees. Wet loose snow activity will be limited in alpine zones but the snow surface is likely to thaw by this afternoon on mid elevation slopes that receive direct sun.  Small isolated areas of loose wet snow instability could occur today on sunbaked slopes in alpine areas and in the trees around rock outcrops and ribs.

The avalanche rose is filled out for alpine (above treeline) and mid elevations in the trees. Areas that are gray do not have snow or there is no snowpack information.

  • Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Loose Wet
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    Unlikely
  • Size ?
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  • Trend ?
    Same

Even though it will be warmer today than yesterday, I think wet loose snow avalanche activity will be minimal. After another few warm days and warming nights, wet snow instability will increase at the mid elevations and possibly in alpine terrain on east to southeast facing slopes.

There is no snow at low elevations which is the reason that the grids are grey in the E and Southeast sections.

Avalanche Problem 2: Persistent Slab
  • Character ?
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  • Likelihood ?
    Certain
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  • Size ?
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  • Trend ?
    Decreasing Danger

Reports of fracture and propagations on buried weak layers are still coming in. The weak layers are either the basal facets and rounding depth hoar or above or below crusts under the cohesive slab formed at the end of February. Deep slab avalanches are unlikely but as long as these layers continue to react in tests, they are an avalanche problem in alpine terrain.  

advisory discussion

Most of California basked in record warmth this winter while the upper Midwest observed a top-10 coldest winter in the last 118 years. Southern California and Inyo and Mono counties experienced a 5 degree F temperature anomaly from December through February. This means the average daily temperature was 5 degrees warmer than the 100 year average.

Strong ridging over the northeast Pacific Ocean and a deep trough over most of eastern Candada and the eastern US was the dominant weather pattern.  This past winter is a good example of how there was a regional cold temperature anomaly in the Eastern and southest US even in a warming climate (http://www.ncdc.noaa.gov/sotc/synoptic/2014/2).

recent observations

Cool protected north facing slopes in the June Mountain area have weak faceted snow at the bottom and above and below sun crusts in alpine terrain. Fractures propagated in two out of three extended column tests on 27 and 29 taps. The overlaying slab was the February 28-March 2 storm snow. While it took many taps to get the column to fracture and propagate, the fact that propagation occurred is more important than the number of taps- those persistent weak layers need a lot of force to activate but they are weak and will remain an avalanche problem probably until the snow melts.  I noted a thick layer of depth hoar at the base of a 3-4 ft deep snowpack but this layer did not react.

 Similar results were reported on an east slope in the Red Cone area in the Mammoth Basin. Observers reported an ECTP 30 on 1 mm facets above a crust about 29 inches down and believed this crust represented the old snow surface prior to the March 7-9 storm.  A week ago, extended column tests show propagation on the old snow/Feb. 28-March 2 storm snow.  This winter’s buried weak layers are different than last year’s because buried weak layers continue to react in tests in March. At the same time last year, wet snow avalanches were widespread.

Depth hoar, June Mtn area                                                                                  ECT, failed on small facets, east slope near Red Cone Mammoth Basin

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 23 deg. F.
Max. temperature in the last 24 hours: 36 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 10-15 mph
Maximum wind gust in the last 24 hours: 38 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 0 inches
weather

A storm will pass to our north Sunday night into Monday bringing a cold front into our region. The big impact from this will be increased winds - with southwesterly gusts 35-45 mph likely across the region with the strongest winds from roughly midnight to 8 am Monday morning. Sierra ridges will see gusts on the order of 80-90 mph with northwest winds.

The long range forecast suggests increasing chances of the storm track returning to our area in a week but as always, stay tuned as forecasts become more accurate as the time for possibly snow grows shorter.

Today will be the warmest and final day of the three day warmup with highs reaching the mid 50’s in the Mammoth area and mid 40’s in the June Mountain and Rock Creek area.  By tonight, north winds will increase as a storm passes to the north. Temperatures fall 10 degrees back to seasonal temperatures with highs in the upper 30’s above 10,000 ft and mid 40’s at mid elevations.  The first part of the week will be windy and cooler.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Sunday Sunday Night Monday
Weather: sun clouds clear windy
Temperatures: 55 deg. F. 25 deg. F. 44 deg. F.
Wind direction: SW SW N
Wind speed: 10-15 25-40 40-50
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Sunday Sunday Night Monday
Weather: sun clear clouds, few
Temperatures: 40 deg. F. 23 deg. F. 35 deg. F.
Wind direction: W N NE
Wind speed: 25-30 50-70 50-60
Expected snowfall: 0 in. 0 in. 0 in.
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