Avalanche Advisory: Tuesday - Dec 17, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 18, 2019 @ 6:44 am
Avalanche Advisory published on December 17, 2019 @ 6:44 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE avalanche danger exists at upper elevations on all aspects with LOW avalanche danger at mid to lower elevations. Fresh wind slab & loose dry snow sloughing will be the primary concerns at upper elevations on specific features in complex or exposed terrain.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Wind slabs, both new and old, have the potential to be lurking on all aspects in the Upper elevations. Winds have been around the compass from W-S during our latest storm, to a predominant northerly pattern (Sun-Mon) and reverting back to Southerly flow today. Today’s southerly winds at perfect loading velocities combined with plenty of available low density snow will potentially re-load the northerly and easterly aspects in the Upper elevations. Although there has not been much evidence of Wind slabs being triggered in the forecast zone, there also have been limited observations up high in more committing terrain. Specific terrain features such as hemmed-in colouirs, areas adjacent to ridgelines, cliff-bands/rock outcroppings, and gully features will be areas to focus on and be on the look out for red flags such as active wind loading, shooting cracks, or fat looking pillows and drifts.

Avalanche Problem 2: Loose Dry
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Many recent observations report excellent soft snow skiing in terrain generally exposed to wind effects. The past few days northerly moderate to mild winds have not totally stripped away the recent snowfall, leaving powdery conditions on a variety of aspects and terrain. Cold overall temperatures have also contributed to pulling moisture from the surface snow and preserving loose soft conditions. With this being said, loose snow sloughing should be considered in steep confined terrain and on convex/unsupported slopes with exposure to fall hazards.

advisory discussion

With Tuesday’s reverse back to increasing southerly winds and plenty of fresh snow in the hills, be on the lookout for blowing snow, recent cornice growth, and fat, pillowed snow surfaces. All these clues can help you identify and steer clear of fresh wind deposits and potential wind slab conditions. Terrain features that are conducive to capturing drifting snow such as the leeward sides of ridgelines, chutes, and cross-loaded depressions should be looked at critically. More extreme terrain features such as steep couloirs may present the most hazards for potential loose snow sloughing right now. Early Season Obstacles Exist!

recent observations
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12/15 -Mammoth Area –Mammoth Crest – Rain Crust & Surface Hoar Layer

Weather and CURRENT CONDITIONS
weather summary

Partly cloudy transitioning to mostly cloudy skies Tuesday before the onset of a predicted quick shot of snow showers for the mountains Wednesday. Temperatures will warm from the previous days to above freezing below 10000ft. Highs in the 20s to low 30s for the high country. Winds have already shifted back to a southerly flow early this morning, and should be relatively moderate for today (10-20+ mph) with some ridge top gusts to 30mph. Wind velocities are expected to increase tonight continuing from the South. Light snow showers, upwards of an inch are possible Wednesday.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Partly cloudy. Slight chance of snow. Snow levels below 7000 feet. Chance of precipitation is 20%.
Temperatures: 29 to 34. deg. F. 16 to 21. deg. F. 25 to 31. deg. F.
Mid Slope Winds: South 10 to 20 mph with gusts to 30 mph. South around 15 mph. Gusts up to 35 mph increasing to 45 mph after midnight. South around 15 mph with gusts to 45 mph.
Expected snowfall: 0 in. 0 in. up to 1 inch. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%. Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 25%.
Temperatures: 25 to 31. deg. F. 11 to 17. deg. F. 17 to 23. deg. F.
Ridge Top Winds: South 15 to 25 mph. Gusts up to 35 mph in the afternoon. South 15 to 25 mph with gusts to 45 mph increasing to 25 to 35 mph with gusts to 55 mph after midnight. South 25 to 35 mph shifting to the southwest 15 to 30 mph in the afternoon. Gusts up to 60 mph.
Expected snowfall: 0 in. 0 in. up to 1 inch. | SWE = less than 0.10 inch. in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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