Mammoth Basin Snowpack Summary - 2015-01-21 07:00

Avalanche Advisory published on January 21, 2015 @ 7:00 am
Issued by Sue Burak - Inyo National Forest
Snowpack Discussion

Here is a season summary of the snowpack in the Mammoth Lakes Basin.

Snowfall from November survived on cold northerly aspects above treeline and in isolated sheltered gully features. The snow metamorphosed into facets and in some areas like the bottom of cliffs and cold sheltered slopes, depth hoar formed but depth hoar distribution is not widespread as it was last year.

A storm in early December (December 3) came in wet and added 5” and almost an inch of water; new snow densities 16 to 18% created a thin supportable skiing surface. After the early December storm, mid-December Mammoth Pass reported 25” of snow with 3.5 inches of water content; last winter (2014) there was 2 inches of water in 22 inches of snow.

A much- advertised but disappointing mid-December storm added 12 to 14” of snow and close to an inch of water and was followed by another 10 inches  on Dec 16. Temperatures dropped and the best skiing of the winter to date was enjoyed by skiers and riders in the Mammoth Lakes Basin. Warming temperatures and one day (December 20th) of mid level clouds, high relative humidity created weather conditions favorable for surface melt. A prominent crust formed in the mild days that followed on many aspects and elevations.

After the last significant snowfall on December 17th, a few inches of snow fell at Christmas with strong southwest winds. The coldest temperatures of the year occurred during the last week of December with a few inches of snow falling along with very strong sustained west and southwest winds. Thin wind crusts and wind slabs formed in mid and high elevation terrain.

During the first week of January, strong northeast and east winds stripped high elevation slopes and formed thick hard wind slabs along the San Joaquin Ridge. In the Mammoth Basin, snow near the top of Red Cone, Hollywood Bowl and the top of TJ Bowl suffered from 36 to 48 hours of sustained wind speeds of 60 mph with gusts exceeding 120 mph.

Temperature variations have been a roller coaster in January, ranging from mild daytime highs in the upper 40’s and 50’s in alpine terrain to days when daytime temperatures only reach the mid 30’s and nights dip down to the teens. The snowpack reacts to variations in temperature gradients that favor faceting for a few days followed by mild days and nights around freezing that favor rounding of facets- then repeat the process every 5 to 7 days.  Over the past few days, I noticed there has not been much range between night time and daytime temperatures. This results in low gradients of temperature in the shallow snowpack which favors facet edges becoming rounded- with a short cooling trend today and tomorrow, processes will probably switch until the weekend when temperatures are expected to be well above normal.

Depth hoar is found in a patchy distribution on northerly slopes at treeline and in alpine areas. It’s hard to pinpoint individual slopes that have depth hoar but the distribution of facets is reliable and widespread. Whether there is depth hoar or facets at the bottom of the snowpack, neither one is producing results in snowpit tests.

recent observations

Recent observations from south facing slopes on the San Joaquin Ridge, show melt freeze conditions on SW and some west aspects, in snow covered areas from 10,000 ft. to 9,000 ft. Below 9,000 ft., snow coverage is patchy.

Clouds and southwest winds blowing 25-30 mph yesterday above McLeod Lake kept the snow surface below freezing. Open areas in the glades above McLeod Lake held soft, recrystallized snow with patchy areas of thin wind crusts. Above treeline, thin wind crusts, slabby, breakable wind layers were interspersed with soft settled snow. 

Lower elevations in the Mammoth Lakes Basin had many areas on the flats and low angle slopes in the trees where the top inch or two of snow were wet. Faceted snow under the surface was rounding and forming clusters. Extended column and compression test results were nil.


CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 25 deg. F.
Max. temperature in the last 24 hours: 42 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: 38 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 18 inches

High pressure builds over the eastern Pacific and the west coast for the week, resulting in benign and boring weather conditions. Inversions may develop unless upper level winds mix down to the 7,000 to 8,000 ft elevations.  Well above normal temperatures are expected for the weekend.

Daytime highs reach the upper 30's today at the 9,000 ft elevation in the Mammoth Basin and low 30's above 10,000 ft. Night time lows will be in the low 20's and teens at mid and high elevations. Northeast winds will pick up today, gusting to 25 mph along the ridges. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: sunny clear sun with some clouds
Temperatures: 39 deg. F. 20 deg. F. 45 deg. F.
Wind direction: NE E W
Wind speed: 15 5-10 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: sun clear sun with clouds
Temperatures: 32 deg. F. 17 deg. F. 38 deg. F.
Wind direction: NE NE W
Wind speed: 15-25 5-15 5
Expected snowfall: 0 in. 0 in. 0 in.

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

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