Eastern Sierra Avalanche Forecast - 1/7/15

Avalanche Advisory published on January 7, 2015 @ 7:05 am
Issued by Sue Burak - Inyo National Forest
advisory discussion

This past week has seen an extreme range in temperatures and winds. A week ago, daytime temperatures struggled to reach 15 F in the Mammoth Basin, followed by two days of sustained high winds; there was an 8 hour period on Mammoth Mountain when the wind blew 80 mph with gusts over 140 mph. The exposed terrain on the San Joaquin Ridge took on the appearance of an inclined agricultural field with alternating furrows of snow and pumice. A week later, the high pressure ridge is still in place but there are no “inside slider” storms slipping over the ridge to bring meager snowfall or strong north east winds

During the wind event last week, a few inches of new snow fell on sheltered slopes in the trees in the Mammoth Basin.  Near surface facets were widespread but no surface hoar was observed. Two December crust layers are the features of interest in a shallow faceted snowpack on north facing slopes in the Mammoth Basin above 9,000 ft.  An extended period of dry weather generally promotes faceting if temperatures are close to the mean for early winter but the rapid and extreme changes in the weather this winter means the snow structure could change in unexpected ways.  

recent observations

Settled powder or “recycled powder” was found in sheltered north facing trees yesterday above Horseshoe Lake along with patchy areas of wet surface snow that formed by mid-morning from  low angle, indirect sunlight. Patchy areas of a thin wind crust formed during last week’s wind event were common in more open areas on slopes exposed to the wind.

Below the variety of snow surfaces, the snowpack remains faceted but facets are rounding off in response to a decreasing temperature gradient. Faceted grains above and below the two crusts are not showing any rounding but they are not growing either. Facets above and below crusts usually are an instability concern but did not react in today’s extended column tests.

weather summary

The National Weather Service wrote this morning: “bottom line is we're not seeing any meaningful signals that the Pacific storm track will return to CA/NV through at least the middle of next week, possibly longer. It isn't unusual for us to see these high pressure ridges set up over us in January for a couple weeks at a time”.  Last year there was no precipitation for 60 days straight; storms started reaching our area at the end of January.

The next few days will be sunny and warm for this time of year. Daytimes highs will reach the upper 40’s at the 9,000 to 10,000 ft. elevations. Nights will cool off to the upper 20’s. Winds will be calm to light breezes to 5 mph.  

Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 30 deg. F.
Max. temperature in the last 24 hours: 54 deg. F.
Average wind direction during the last 24 hours: w
Average wind speed during the last 24 hours: 5 mph
Maximum wind gust in the last 24 hours: 15 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 21 inches
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 mostly clear partly sunny
Temperatures: 46 deg. F. 33 deg. F. 44 deg. F.
Mid Slope Winds: S calm W
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: sun partly cloudy partly sunny
Temperatures: 38 deg. F. 29 deg. F. 34 deg. F.
Ridge Top Winds: S SW W
Expected snowfall: 0 in. 0 in. 0 in.
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