Avalanche Advisory: Tuesday - Dec 18, 2018

THIS AVALANCHE ADVISORY EXPIRED ON December 20, 2018 @ 6:21 am
Avalanche Advisory published on December 18, 2018 @ 6:21 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

For Tuesday small human triggered wind slab avalanches may be possible in isolated areas on upper elevation slopes that face SE-E-N-NW.  

For Wednesday wind slab avalanches will be overall unlikely, but not impossible in the same isolated upper elevation areas as Tuesday.  Small loose wet point releases will be possible as slopes next to rocks warm from the sun on SE-S-SW facing slopes.  

Thin snowpack! Early season obstacles exist!

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Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

3-5” of new snow fell Monday morning accompanied by moderate SW winds thru the afternoon.  Snow could be seen rolling over ridgelines and across open slopes at mid to upper elevations.  While 3-5” of snow is not much, it is enough for winds to form small wind slabs, and at least one small natural avalanche was reported.   Winds decreased yesterday (Monday) afternoon, which has given these small wind slabs some time to stabilize.  However, there may be some wind deposits that remain sensitive to human triggering today (Tuesday), and as SW winds increase again this afternoon, some small new wind slabs could form.  Watch for pockets of unstable snow on the leeward side of ridges, sidewalls of gullies, and around other features that promote drifting at upper elevations on SE-E-N-NW facing slopes.  Cornices and wind ridges are clues that could let you know where these slabs exist.  While a resulting avalanche is likely to be small, it could lead to a nasty fall in steep rocky terrain.  

For Wednesday, risk of triggering a small wind slab will become even less.  However with lighter winds, even warmer temperatures reaching the mid 40s around 10,000’, and most importantly sunny skies, small loose wet point releases will become possible on SE-S-SW slopes next to rocks as they warm from the sun.  

advisory discussion

Prior to yesterday (Monday) morning’s light snowfall, snow surfaces in areas with any kind of exposure were firm and variable to say the least, and in sheltered northerly areas thin and faceting.  In terms of avalanches very little stability concerns existed.  The biggest concern would be if a substantial snowload fell ontop of areas with faceting snow near or on the surface, but we haven’t had that yet (perhaps in the future?). The largest safety concern by far is the shallow snowpack with plenty of rocks, logs and stumps pocking thru or just barely buried waiting to snipe someone.  The other main concern is firm surfaces where a fall would be hard to self-arrest.  Ice ax and crampons are a good idea for adventures on exposed higher elevation terrain. Let’s hope for more snow soon!! 

recent observations

-A small storm brought in 3-5” of snow yesterday morning with moderate SW winds which decreased in the afternoon.  

-Observers in the Mammoth Crest area reported lots of wind transport over the crest thru at least mid-day describing it as a “cauldron of snow overflowing over the ridgeline onto northerly slopes”.  They also observed at least one small D1 natural avalanche on the higher north slope of Red Cone Bowl.   Click here for observation details.

-Mammoth Mtn Ski Patrol reported small loose dry D1 avalanches as a result of ski cuts mid-mountain yesterday.  

-12/17 – Mammoth Area – Solitude Ridge: 3-4” of new snow on top of variable firm surfaces with no observed instabilities. 

-12/17 - Mammoth Area - Sourounding ridges: Mid-day snow transport and stripped ridgelines.

weather summary

For Tuesday expect partly cloudy skies, light SW winds increasing in the afternoon with gusts up to 60mph over ridgetops, and above average temperatures reaching ~40degrees at 10,000’.  

For Wednesday expect sunny skies, light SW winds with gusts in the 30s at upper elevations, and even warmer temperatures reaching the mid 40s at 10,000’.    

High pressure will continue to build thru the week and into the weekend with continued above average temperatures before chances increase for unsettled weather and light snowfall Sunday night into early next week.

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. Clear. Sunny.
Temperatures: 40 to 46. deg. F. 26 to 32. deg. F. 45 to 50. deg. F.
Mid Slope Winds: Light winds becoming west 10 to 15 mph with gusts to 45 mph in the afternoon. West 10 to 15 mph in the evening becoming light. Gusts up to 40 mph. Light winds. Gusts up to 30 mph in the morning.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Clear. Sunny.
Temperatures: 36 to 41. deg. F. 25 to 30. deg. F. 41 to 46. deg. F.
Ridge Top Winds: Southwest 15 to 25 mph with gusts to 45 mph increasing to 25 to 35 mph with gusts to 60 mph in the afternoon. West 15 to 30 mph. Gusts up to 55 mph decreasing to 45 mph after midnight. Southwest 15 to 20 mph. Gusts up to 35 mph decreasing to 25 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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