Mammoth Basin Snowpack Summary - 2015-04-01 07:10

THIS ADVISORY EXPIRED ON April 4, 2015 @ 7:10 am
Avalanche Advisory published on April 1, 2015 @ 7:10 am
Issued by Sue Burak - Inyo National Forest
Avalanche Character 1: Normal Caution
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Use normal caution when travelling in the backcountry.

Snow surfaces will be firm and icy above treeline. Beware of slide for life conditions.

Snowpack Discussion

Morning temperatures are running 10-15 degrees colder than yesterday morning and strong southwest winds are blowing 40-60 mph over the ridgetops.  On warm solar aspects facing east and southeast and mid elevation north facing slopes, melt water has been percolating through the February layer. In contrast, shaded north facing slopes above treeline are still cool and dry and continue to show faceting in the upper snowpack.

As temperatures fall to below normal for at least a week, melting will cease on solar aspects, gradients of temperature will increase and drive more faceting. If snow comes, the avalanche problem will become wind slabs. Welcome to April.

This winter’s weather patterns created an unusual pattern of storm snow sandwiched between alternating melt freeze and sun crusts. Crusts foster faceting by inhibiting vapor diffusions and intensifying adjacent temperature gradients. Over time, faceting processes have recycled the entire snowpack into coarse snow and the multi layers of crust/facet combinations have been transformed into density changes rather than crusts.

recent observations

Gusty winds and firm icy snow conditions were prevalent yesterday above Horseshoe and McLeod Lakes. Despite the warm weekend temperatures that created more bare areas in the Lakes Basin, the snowpack above treeline on northerly is not melting- snow surfaces are firm and wind affected and a few areas on east facing slopes had a thin sun crust. Yesterday the coldest snowpack temperature was -3 C at 10 and 20 cm below the surface in a snowpit dug at 10,300 ft. in the Mammoth Crest area. Compression test continue to fail in the hard range on facets below the February layer about 50 cm down from the surface of the snow.

A snowpit dug on Minaret Summit last Friday found multiple pencil and knife hard crusts and ice layers with rounding facets between the crusts. The early February layer was not present on this northeast aspect at 9,300 ft.

The Minaret Summit profile from 9,300 ft., northeast aspect shows multiple layers but the thick February layer I broke a snow saw on, is not observed in this location.


CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 33 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 40 mph
Maximum wind gust in the last 24 hours: 55 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 20 inches

After a solid refreeze last night, temperatures are in the mid to upper 20’s this morning. After enjoying days of warm late spring weather, April roars in bringing a pattern change that could last for over a week. A series of shortwaves will hit the West coast tonight and Saturday into Sunday. There is some moisture associated with these systems, especially over the weekend and early next week.

Daytime highs have dropped 15 to  20 degrees from weekend highs that reached 60 in the Mammoth Lakes Basin- expect temperatures at the 9,000 to 10,000 ft. elevations to reach the upper 30’s and low 40’s through the weekend. Alpine terrain will be cold with highs around freezing and lows in the teens. Winds today will be moderate to strong over the ridgetops, gusting up to 50 mph from the southwest.    

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: sun with clouds partly cloudy Sunny
Temperatures: 40 deg. F. 39 deg. F. 43 deg. F.
Wind direction: SW SW SW
Wind speed: 15-30 15-25 10
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Wednesday Wednesday Night Thursday
Weather: Clear, winds breezy to windy clear, winds breezy to windy Sunny
Temperatures: 32 deg. F. 17 deg. F. 31 deg. F.
Wind direction: SW SW W
Wind speed: 25-35 15-30 20-25
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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