Avalanche Advisory: Wednesday - Jan 2, 2019

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THIS AVALANCHE ADVISORY EXPIRED ON January 4, 2019 @ 6:59 am
Avalanche Advisory published on January 2, 2019 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Avalanches will be unlikely for Wednesday and Thursday, but not impossible.  Isolated small wind slabs sensitive to a human trigger could linger in complex upper elevation SE-S-W-NW facing slopes.   Beware of Early season obstacles, as well as firm conditions in exposed terrain. 

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Below Treeline
Avalanche Problem 1: Wind Slab
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NE winds have been blowing with force for a solid week since Christmas day.  While loose snow is becoming scarcer and scarcer in exposed areas, small amounts of snow could still be seen getting blown over ridge tops yesterday (Tuesday).  In isolated upper elevation spots on SE-S-W-NW facing slopes, some of this transported snow likely settled into small fresh wind slabs that could still be sensitive to a human trigger today (Wednesday).  Finding a sensitive wind slab that hasn’t stabilized on Thursday will become even less likely as winds finally become light on Wednesday and Thursday.  Remember that even during low avalanche danger avalanches can happen, as we saw on Sunday when 2 skiers were caught and flushed out of the SE Gully on Mt. Baldwin (click here for details).  If you are traveling into the alpine, keep your eyes out for a small potentially sensitive wind slab just below ridgelines, on the sidewalls of gullies, and around other features that promote drifting.  On southerly facing slopes keep in mind that sunny skies and low winds could warm one of these potentially sensitive small wind slabs, especially if it is sitting on top of a weak layer, making it even more sensitive around mid-day.  

Regardless of where you go always practice and reinforce good travel habits such as exposing one person at a time, good communication, and carrying the right gear.  Good habits save lives.  You never know when a surprise could happen.

advisory discussion

The avalanche that occurred on Sunday is a good reminder that even during relatively low avalanche danger, avalanches can happen, even natural ones.  Thankfully no one was seriously injured.  Click here for a thoughtful detailed account from the party involved.   While the avalanche danger was unlikely for that day, this avalanche did occur in the type of terrain that the advisory mentioned would be possible for wind slabs that day. We don’t know for certain what triggered this natural release on this SE facing terrain, but it seems very likely that is was a wind slab recently formed by strong NE ridge-top winds.  Perhaps it was simply current wind loading that overburdened the slope.  Perhaps there was a weak layer underneath involved.  Perhaps the mid-day sun and relatively warm air temperatures warmed the slope enough to cause an already fragile structure to fail.  Regardless of the exact cause, the message is not to let your guard down in the mountains.    

Clear and cold nighttime conditions thru this week will continue the faceting and weakening of our thin snowpack.  While not a stability concern now, if we get 1-2ft of new snow-load this weekend, it could definitely become one.  Keep digging into the snowpack to see where this sugary facet formation is happening.  Also, feathery surface hoar formation has been reported on the surface of the snow in some places over the weekend.  This can become a dangerous weak layer if it persists on slopes steep enough to avalanche if it gets buried.  Please let us know if you see any of these feathery formations persisting on slopes. 

Weather and CURRENT CONDITIONS
weather summary

High pressure will remain in place thru this week keeping conditions clear and dry.  Expect temperatures to rise into the mid 30s today (Wednesday) and into the upper 30s on Thursday near 10,000’.  After a week of strong NE winds, winds are finally on the decrease.  For today (Wednesday) NE winds will decrease into the realm of light, switching around to the S tonight, and then quite light out of the SW for Thursday. Clouds return on Friday ahead of a promising looking storm on Saturday, which models at this point are showing could bring a couple of feet of snow to the mountains. 

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: Sunny. Clear. Sunny.
Temperatures: 34 to 39. deg. F. 19 to 24. deg. F. 39 to 44. deg. F.
Mid Slope Winds: Light winds. Gusts up to 25 mph in the morning. Light winds. Light winds.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny. Clear. Sunny.
Temperatures: 30 to 35. deg. F. 20 to 25. deg. F. 34 to 39. deg. F.
Ridge Top Winds: Northeast 15 to 20 mph. Gusts up to 30 mph in the morning. South 10 to 15 mph. Southwest 10 to 15 mph.
Expected snowfall: 0 in. 0 in. 0 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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