June Mountain Area, Mammoth Basin Snowpack Summary - 2015-03-20 07:10

Avalanche Advisory published on March 20, 2015 @ 7:10 am
Issued by Sue Burak - Inyo National Forest
Avalanche Character 1: Loose Wet
Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

After a solid refreeze of the snowpack last night at elevations above 9,000 ft. , the snow surface won’t get soft and wet until later in the day. Avoid terrain traps where even a small sluff can pile snow up deeply.

Water has ponded and pooled above crusts in the snowpack at the 9,000 to around 9,700 ft. elevations in the Lakes Basin and a few small, isolated wet loose avalanches occurred early this week. In alpine terrain, there is no sign of percolating melt water. After today, cooler temperatures, windy conditions and a snowfall will lock up the snowpack until middle of next week.  


Snowpack Discussion

This season has been a series of small storms followed by several days of clear skies and mild temperatures. The pattern started in December and continued through the warm month of January. February had the unforgettable rain and dense wet snow storm that occurred the first weekend, followed more 5 to 6 day cycles of warm days, warm nights until the end of February. A cold storm dropped 12-18” of light dry snow with little to no wind creating the best skiing and riding conditions of the year.  

This week’s warmup cycle saw limited wet loose avalanche activity in the Negatives and in a few places below the Mammoth Crest and Duck Pass. Wednesday’s and last night temperatures finally dropped into the mid to upper 20’s for 8 hours at Mammoth Pass, giving a solid freeze to the spring like snow at mid elevations. Alpine elevations had 10 to 12 hours of temperatures in the low to mid 20’s. With another good freeze last night under clear skies, the melting mid elevation snowpack will have less time to melt before cooler temperatures, strong winds and a chance of snow puts everything on hold into early next week.

Alpine snowpacks are colder and north aspects get less direct sun than mid elevation snow. Snow in gullies and on open slopes is moist and continues to show it is well bonded to the early February layer. But a report yesterday from a 40 degree site on Roger's Right from Ned Bair showed deep instability about 20 inches down- ECTP 20  on 4F to F hard rounding facets. This result shows that alpine snowpacks have weak faceted snow under layers deep in the pack that can be unpredictable.  As the days get longer,  melt water will move down and pond on crusts and density changes that overly weak snow.


recent observations

Snow surfaces were hard and icy yesterday morning but by early afternoon, frozen crusts softened and travel in trees between 9,000 and close to 10,000 ft. was occasionally interrupted by breaking through the surface crust on wet facets to the February layer. Above treeline, consolidated moist old powder is widespread and there was no sign of recent wet avalanches.

Snowpack at 10,800 ft. TJ Bowl area











Snowpack at 9,500 ft.








CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 23-29 deg. F.
Max. temperature in the last 24 hours: 40 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 25-30 mph
Maximum wind gust in the last 24 hours: 40-50 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 36 inches

Skies are clear, and stations are reporting morning temperatures below freezing at the 9,000 ft. elevation.  Elevations above 10,000 ft. are in the low to mid 20’s. Winds are blowing from west and southwest at 15-25 mph and will increase by the afternoon as cooler air pushes into northern California.  The weekend will be windy and cooler with winds increasing to advisory levels Sunday afternoon and evening as a cold front brings a chance of snow to the area.

Daytime highs will reach the low to mid 50’s at the 9,000 to 10,000 ft. elevations. Higher terrain will see highs in the mid 40’s.

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: sunny mostly cloudy mostly sunny
Temperatures: 50-54 deg. F. 32-35 deg. F. 42 deg. F.
Wind direction: SW SW SW
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: mostly sunny clear, brezzy clear, windy
Temperatures: 40-45 deg. F. 28-30 deg. F. 33-35 deg. F.
Wind direction: SW SW SW
Wind speed: 10-15 20-35 25-35
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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