Mammoth Basin Snowpack Summary - 2015-01-31 07:00

THIS ADVISORY EXPIRED ON February 2, 2015 @ 7:00 am
Avalanche Advisory published on January 31, 2015 @ 7:00 am
Issued by Sue Burak - Inyo National Forest
Snowpack Discussion

Another inch or two of snow fell over the last two days as low clouds obscured the Sierra Crest. Cooler temperatures and light winds preserved stellar crystals sitting on thin to thick melt freeze crusts in the Mammoth Lakes Basin above 9,000 ft.

Snowpack observations from earlier in the week showed thick melt freeze crusts from 8,500 ft. to around 9,400 ft. and thin melt freeze crusts on shaded north facing slopes above 9,400 ft. and warmer snow temperatures resulting from last weekend’s mild 50-55 degree days and clear skies.

A shallow snowpack means trends in daytime and night time temperatures affect snow temperatures in the upper 8 to 12 inches of the snow. Yesterday’s snow temperature profile show the effect of the last three days of cooler daytime and night time temperatures.  The rounded facets showing more angular shapes and facets had formed under the various melt freeze crusts of last weekend. Cool temperatures and little wind preserved the new snowfall’s stellar crystals.

Repeated cycles of warming and cooling temperatures this month affect the upper 8 to 12 inches of a shallow 20 to 30 inch deep snowpack. Facets round as temperature gradients decrease during warming and rounded facets become angular as temperatures cool to near seasonal January temperatures.  What appears to remain unchanged despite reversals in temperature gradients is the overall snowpack strength.Tests continue to be shovel pounding exercises. 

With the possibility of a storm approaching the area next Thursday/Friday, and if snowfall amounts to more than a few inches, faceting under the melt freeze crusts may become problematic with what we hope is a significant storm load.  

recent observations

Another inch or two of snow fell above 9,000 ft. over the last two days as low clouds obscured the Sierra Crest. Very light snow showers dropped another inch yesterday at stations in the local area. This little bit of new snow remained light and cold yesterday due to cool daytime temperatures that never got above freezing. Light southwest winds at the top of Mammoth veered to the northeast Friday morning and increased in intensity during the day.

Temperature gradients in the shallow, 20-30 inch snowpack have increased as day time temperatures fell from highs in the 50's to yesterday's high of 32 F.  Snow surface conditions consisted of 0.5 to 2 inches of recent new snow on top of supportable or breakable thin crusts. Snow cover is thin at 8,500 ft. with bare patches on flat ground on Panorama Dome. Snowpack depths increase to 18- 24 inches around Lake Mary and snowpack depths at higher elevation on north facing terrain  are holding steady at 24-30 inches. Near surface crust facets continue to develop and the entire pack is facets and rounded facets with occasional appearances of depth hoar.  Snowpit tests are not producing any results. 

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 24 deg. F.
Max. temperature in the last 24 hours: 32 deg. F.
Average wind direction during the last 24 hours: NE
Average wind speed during the last 24 hours: 40 mph
Maximum wind gust in the last 24 hours: 70 mph
New snowfall in the last 24 hours: 1 inches
Total snow depth: 19 inches

Daytime highs reach the mid to upper 40’s today at the 9,000 ft. elevations. Northeast winds gusting to 45 mph are expected at these mid elevations. Daytime highs above 10,000 ft. reach the mid-30’s today. Expect strong northeast winds that will diminish by tonight. Temperatures at the mid and higher elevations will remain in the upper 30’s and 40’s through the weekend. Nights will reach freezing at the 9,000 ft. elevations and in the mid 20’s above 10,000 ft.

Forecasters are watching model drop the storm track farther south for next week and confidence is increasing for an atmospheric river to reach the west coast by Friday.

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: Windy mostly clear mostly sunny
Temperatures: 45 deg. F. 33 deg. F. 46 deg. F.
Wind direction: NE NE E
Wind speed: 30-45 10-15 10
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Windy mostly clear sunny
Temperatures: 37 deg. F. 26 deg. F. 40 deg. F.
Wind direction: NE NE NE
Wind speed: 30-50 10-15 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.

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