Mammoth Basin Snowpack Summary - 2015-05-02 07:05

THIS ADVISORY EXPIRED ON May 4, 2015 @ 7:05 am
Avalanche Advisory published on May 2, 2015 @ 7:05 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.

Warning signs of wet snow instability are

  • Roller balls (pinwheels) in new snow that is getting wet for the first time
  • Natural or human triggered wet sluffs
  • Small sluffs fanning out into larger slides, or running long distances
  • Punchy or collapsing crusts


Snowpack Discussion

This is the final snowpack summary of the 2014-2015 season.

Thanks to Ned Bair and Preston Few for your observations and discussions. Thanks to Chris Smallcomb and Zach Tolby at the National Weather Service office in Reno for providing avalanche weather forecasts.

Spring snow is found on high elevation north to east facing slopes.  Spring skiing conditions, where there is snow, are quite good.  The peak of wet loose snow activity occurred mid-week but continue to watch for wet loose snow slides as the sun heats up the snow, especially around rocks, outcrops, and cliff bands.  Expect firm spring snow conditions this morning with midday softening.  As usual, you should get out early and get home by early afternoon.

Nighttime low temperatures at the 10,000 to 11,000 ft. elevations have been in the mid 30’s.  Areas where cold air pools like Ellery Lake have seen cooler temperatures around 30 degrees.  When nighttime low temperatures are above freezing, the snow warms up rapidly.  If skies are cloudy overnight, you can expect wet snow by mid-morning because clouds emit longwave radiation thus cloudy nights are warmer than clear nights.

When the snow gets a good refreeze, wet loose avalanche conditions can occur later in the day. You can use the Mammoth Mountain Ski Patrol site, or   to monitor  air temperatures. The usual advice to move to another slope and aspect if wet loose snow slides occur on the slope you are on is good practice and works in deeper snowpacks. This spring, snow coverage is sparse so each situation will require a different strategy to avoid getting pushed into a terrain trap.

There is about a meter of snow above 10,500 ft. in the north facing high elevation terrain in the Mammoth Basin and the Tioga Pass area. Approaches require hiking.  

17 storms accounted for the season snowfall of 116 inches, including a late season storm that dropped 21 inches the first week of April. The long term average winter snowfall at the Mammoth Mountain ski patrol study plot (1983-2014) is 350 inches; winter snowfall in 2015 measured a depressing 116 inches.


CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 32 deg. F.
Max. temperature in the last 24 hours: 45 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 30-40 mph
Maximum wind gust in the last 24 hours: 50 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 0 inches

Above average temperatures will remian well above normal through the weekend. Thunderstorms are possible each afternoon with the best chance of thunderstorms occurring on Sunday and Monday.  Night time lows above 10,000 ft will be in the low to mid 30’s with daytime highs reaching 60 F.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Saturday Saturday Night Sunday
Weather: isolated thunderstorms isolated thunderstorms widespread thunderstorms
Temperatures: 61 deg. F. 38 deg. F. 61 deg. F.
Wind direction: SW SW SW
Wind speed: light 5+10 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: isolated thunderstorms isolated thunderstorms widespread thunderstorms
Temperatures: 50-55 deg. F. 37 deg. F. 50-52 deg. F.
Wind direction: SW SW S
Wind speed: 10-20 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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