Mammoth Basin Snowpack Summary - 2015-12-10 09:12

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THIS ADVISORY EXPIRED ON December 12, 2015 @ 9:12 am
Avalanche Advisory published on December 10, 2015 @ 9:12 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center
Snowpack Discussion

The recent unseasonably warm post-storm temperatures has formed mostly supportive melt-freeze crusts on southerly aspects while more northerly aspects have crusts with variable supportiveness with little if any soft snow at mid to lower elevations. Additionally,the Chinook like winds have further scoured many westerly aspects, forming wind loaded pockets and wind slabs on leeward slopes in the upper elevations on top of decomposing grains mixed with graupel. Overall the snowpack is shallow and variable, primarily consisting of facets at or near the surface that likely will not support the anticipated snowfall from the approaching storm system, which may produce as much as much as 3 feet of new snow with high winds.

 

recent observations

The recent strong winds and unseasonably warm weather has greatly impacted the snow condition, with little if any soft snow at mid to lower elevations. Instead we have a mix of supportive to unsupportive crusts on most aspects. On more northerly aspects, facet formation has been ongoing coupled with the presence of a persistent weak layer of 2 mm facets approximately 20 cm down from the snow surface.

Stability tests near Red Cone show moderate failures (CTM 16, 19, 17, all Q2) 17cm from the surface on a 30 degree slope. A 1cm layer at ground was comprised two to three millimeter facets that have consolidated into a basal crust which could act as a bed surface for slides initiating in the upper snowpack and possibly stepping down to this layer.

CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: Mammoth 20.4 ° deg. F.
Max. temperature in the last 24 hours: Mammoth 37.2 ° deg. F.
Average wind direction during the last 24 hours: June SW - E, Mammoth Westerly
Average wind speed during the last 24 hours: June 12 - 55, Mammoth 27-81 mph
Maximum wind gust in the last 24 hours: Mammoth 100 mph
New snowfall in the last 24 hours: June 0, Mammoth 0 inches
Total snow depth: Mammoth 36 inches
weather

Thursday - A stronger than average winter storm is still on track to impact the Sierra and western Nevada. Winds increasing with gusts up to 40 mph along the Sierra front. These winds will continue to increase overnight as a jet max moves onshore. Gusts will peak overnight with highest peaks over 13000 feet gusting to 150+ mph. Precipitation will move into the Sierra in two different waves. The first, and heaviest, late tonight and early tomorrow morning. The second will arrive Thursday night. Snow levels will begin around 8000 feet then falling to about 6500 feet early Thursday morning. Snow amounts along the crest have been increased to 1-3 feet. Travel in the Sierra is discouraged. Snow levels to fall below 6500 feet, by 5 am. Snow will accumulate down to valley levels with 6-18.  Snow showers will begin to taper off Friday by the afternoon with lighter accumulations possible in the Sierra especially in Mono County conditions will be fairly benign Saturday with a lull between storms.

Friday, the snow will diminish with isolated-scattered snow showers mainly near the Sierra. Cooler conditions will prevail across the region with highs only in the 30s to lower 40s.  A short break in precipitation is expected across most of the region Friday night, before we head into more active weather again for the weekend with the most significant weather impacts expected on Sunday. Cool temps will continue on Saturday with widespread cloud cover, and winds increasing in higher elevations during the afternoon. Gusty winds may begin to spread into lower elevations by Saturday night.

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: CLOUDY. RAIN IN THE MORNING. SNOW THROUGH THE DAY. CLOUDY. SNOW. CLOUDY THEN BECOMING MOSTLY CLOUDY. SNOW SHOWERS. LIKELY IN THE MORNING THEN CHANCE OF SNOW SHOWERS IN THE AFTERNOON.
Temperatures: 35 TO 43 deg. F. 12 TO 19 deg. F. 24 TO 30 deg. F.
Wind direction: SOUTHWEST SOUTHWEST SOUTHWEST
Wind speed: 65 TO 75 MPH WITH GUSTS TO 110 MPH 50 TO 55 MPH WITH GUSTS TO 80 MPH DECREASING TO 40 TO 45 MPH WITH GUSTS TO 65 MPH AFTER MIDNIGHT 35 TO 40 MPH WITH GUSTS TO 60 MPH BECOMING NORTHWEST 25 TO 30 MPH WITH GUSTS TO 45 MPH IN THE AFTERNOON
Expected snowfall: 4 TO 8 in. 4 TO 8 in. 1 TO 4 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: CLOUDY. SNOW. CLOUDY. SNOW. CLOUDY THEN BECOMING MOSTLY CLOUDY. SNOW SHOWERS LIKELY IN THE MORNING...THEN CHANCE OF SNOW SHOWERS IN THE AFTERNOON.
Temperatures: 31 TO 39 deg. F. 9 TO 15 deg. F. 13 TO 20 deg. F.
Wind direction: SOUTHWEST SOUTHWEST WEST
Wind speed: 75 TO 85 MPH. GUSTS UP TO 125 MPH DECREASING TO 115 MPH IN THE AFTERNOON. 60 TO 65 MPH WITH GUSTS TO 100 MPH BECOMING WEST AND DECREASING TO 40 TO 45 MPH WITH GUSTS TO 70 MPH AFTER MIDNIGHT. 40 TO 45 MPH WITH GUSTS TO 65 MPH BECOMING NORTHWEST 30 TO 35 MPH WITH GUSTS TO 50 MPH IN THE AFTERNOON.
Expected snowfall: 4 TO 10 in. 5 TO 9 in. 1 TO 4 in.
Disclaimer

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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