Mammoth Basin Snowpack Summary - 2015-01-23 07:00

Avalanche Advisory published on January 23, 2015 @ 7:00 am
Issued by Sue Burak - Inyo National Forest
Snowpack Discussion

Cold temperatures over the last few days renewed the faceting process at the snow surface and increased temperature gradients within the snowpack on north facing slopes above 9,000 ft. Southern and west facing slopes remain firm, icy and frozen until the afternoon.  A slow warming trend brings daytime highs from the upper 30's on Thursday to close to 50 degrees over the weekend. Expect damp to wet snow surfaces on south to west facing slopes to form by the weekend.

Looking back on the snowpack records at Mammoth Pass from the 6 year drought from 1987 to 1992, one can see that those drought years had more snow than the current dry period. Using data from the snow pillow at Mammoth Pass, 2012 was the driest year in terms of snowpack water content of the current drought years, with 12.6 inches of water in the snowpack around the first of April.   In 2012, snowpacks were shallow running around 24 inches of snow depth until the end of February when a series of storms added 6 inches of water and 5 feet of snow in March.

The numbers from the 2013 winter are surprising- 2013 was a decent snowpack year. There was 7 ft. of snow on the ground on April 1 and over 34 inches of water in the snowpack- that’s about 80% of the long term average.

During the 1987-1992 drought, snowpack water contents averaged about 24” of water and most of the snow came late, in February, March and early April. Last year (2014), there was 17” of water and about 4 ft. of snow in the first week of April, similar to the dry winter of 2007.

Most of last winter’s snow came in February, March and early April. Snowpack water contents during the 1987-1992 drought look pretty good compared to 2012 and last year.

recent observations

Recent observations from the Minaret Summit area continue to show snow on sheltered and shaded north facing slopes remain cold with soft, sugary near surface facets on the surface, and facets composing the snowpack. Wind crusts and the December 20th crust are faceting and losing integrity. Depth hoar is found in patchy distribution and an avalanche class in the Minaret Summit area managed to get the depth hoar layer to fail in a compression test. The fracture character was sudden collapse, causing a noticeable displacement in the column. As alarming as that may sound, no results came from nearby Rutschblock tests.

Facets were found under thick wind slabs that formed during the early January northeast wind event along the San Joaquin Ridge but the layer did not react in extended column tests. A faceted snowpack is usually thought of as a weak snowpack- last year at this time, there was a scary 4 to 8 inch layer of depth hoar that repeatedly failed in extended column tests but depth hoar is not as well developed this winter and there has been only one stability test that has failed on depth hoar.  

North facing slopes in the Minaret Summit area.

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: 45 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 20-40 mph
Maximum wind gust in the last 24 hours: 46 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 19 inches

The National Weather Service office in Reno is suffering drought fatigue just like the rest of us. We would all like to see a weather pattern change but there are no prospects for a week. A cut off low from the south may wander north and east and give us some high elevation snow on Tuesday and Wednesday but forecasters are taking a prudent wait and see attitude.

It’s the same story- high pressure builds over the eastern Pacific and the west coast for the weekend and a slow warming trend will bring daytime highs 10 to 15 degrees above normal temperatures for this time of year. Daytime highs are forecasted to reach 400 F today with northeast winds gusting to over 30 mph over the ridgetops. Temperatures will reach 500 F over the weekend. Night time lows will be above freezing and by Saturday night, there may be no refreeze with lows only around 400 F.

Above 10,000 ft. daytime highs will reach freezing (320 F) today and only warm a few degrees to the low 40’s for the weekend. Northeast winds are expected through Sunday. Night time lows will be around freezing.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: breezy, clear windy windy
Temperatures: 45 deg. F. 29 deg. F. 48 deg. F.
Wind direction: NE NE NE
Wind speed: 10-15 15-20 20-30
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: Breezy windy windy
Temperatures: 32 deg. F. 30 deg. F. 41 deg. F.
Wind direction: NE NE NE
Wind speed: 15-20 20-30 25-45
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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