Mammoth Basin Snowpack Summary - 2015-03-25 07:10

THIS ADVISORY EXPIRED ON March 27, 2015 @ 7:10 am
Avalanche Advisory published on March 25, 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.

Today, new snow will receive the brunt of strong late March sun. Rapid warming of the new snow will destabilize the surface snow quickly. People may be able to trigger shallow wet loose sluffs on steep slopes. 

Snowpack Discussion

The unsettled cool weather that brought 3 to 4 inches of new snow and graupel is coming to an end. Yesterday in the Red Cone Bowl area, soft new snow warmed during the day under cloudy skies, calm winds and mild temperatures right around 40 F.  Wind slabs had formed in the bowl and along the ridgelines and were sitting on top of irregular patterns of frozen wet snow. If additional snowfall occurred last night, it could be possible to trigger a small wind slab in steep terrain today. 

Thin wind slabs were interspersed with areas of old frozen wet snow surfaces. Extended column tests done at treeline above Horseshoe Lake and above treeline propagated and produced sudden planar results with the column failing on ball bearing facets below the February rain layer. Watch out for buried weak faceted snow in places where the snowpack is thin- below cliff bands, in rocky areas and all places where the snow thins out.

New snow will get the first shot of late March solar radiation today and wet snow sluffs could be triggered on steep slopes. Natural wet loose snow slides will be possible ove the next few days in alpine terrain where new snow accumulations of 4 to 6" from Monday and Tuesday nights snowfall. 

recent observations

Yesterday's observations in the Red Cone Bowl area showed 3 to 4 inches of new snow and graupel had accumulated in sheltered locations in the treed slopes  above Horseshoe Lake. On the more wind exposed slopes in the main bowl, accumulations of up to 6 inches were found in protected areas on the back side of terrain features or human created terrain features. Areas of icy frozen melt freeze crusts rounded out the variable surface conditions.

After 10 days of generally stable conditions shown by no results from compression and extended column tests, today's results were surprising. Columns popped off of a slick crust buried under the February rain/dense snow layer about with rounding facets about 20 inches down. Similar results were common in early March but recently, tests have not produced any failures.

High elevation snow in the bowl did not have any signs of surface melt water moving down through the pack as is commonly seen in mid elevations.











CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 27 deg. F.
Max. temperature in the last 24 hours: 43 deg. F.
Average wind direction during the last 24 hours: WNW to NE
Average wind speed during the last 24 hours: 15-20 mph
Maximum wind gust in the last 24 hours: 35 mph
New snowfall in the last 24 hours: 3 inches
Total snow depth: 7 inches

Clearing skies, warming temperatures and light easterly winds are forecasted for today and herald the beginning of yet another warming trend through Friday. Breezy northeast winds could gust up to 25 mph at mid and high elevations.

The weekend could be wet with a few snow showers possible. Long range forecasts call for cooler temperatures and a wet April and May.


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 Sunny
Temperatures: 47 deg. F. 31 deg. F. 51 deg. F.
Wind direction: North NE East
Wind speed: 10-15 5 5
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: Breezy and clear clear sunny
Temperatures: 43 deg. F. 27 deg. F. 45 deg. F.
Wind direction: NE NE E
Wind speed: 15-30 5-10 5-10
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.

-- placeholder --

ESAC receives significant financial support from ...