Eastern Sierra Avalanche Advisory - 3/4/17

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THIS AVALANCHE ADVISORY EXPIRED ON March 5, 2017 @ 6:42 am
Avalanche Advisory published on March 4, 2017 @ 6:42 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
bottom line

Very high winds from the SW will likely form isolated windslabs today at all elevations in areas where loose snow still exists for transport.  These potentially sensitive wind slabs are most likely to be found in areas that are typically somewhat sheltered from less-strong winds.  Human triggered avalanches will be possible, and Natural avalanches unlikely.  Do your own localized assessment of wind slab sensitivity before committing to steep terrain, and if traveling near ridges beware of cornices!

How to read the advisory

Bottom Line

Very high winds from the SW will likely form isolated windslabs today at all elevations in areas where loose snow still exists for transport.  These potentially sensitive wind slabs are most likely to be found in areas that are typically somewhat sheltered from less-strong winds.  Human triggered avalanches will be possible, and Natural avalanches unlikely.  Do your own localized assessment of wind slab sensitivity before committing to steep terrain, and if traveling near ridges beware of cornices!

Avalanche Problem 1: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small
  • Trend ?
    Increasing Danger

Isolated windslabs will become an increasing concern as SW winds which began yesterday around noon continue to increase throughout the day today with gusts reaching into the 120mph range over high elevation ridgetops, and into the 40mph range below 8000’.  As most exposed slopes at mid to upper elevations were highly wind-effected by the high winds associated with this past Monday’s storm, slightly more sheltered areas at lower elevations that still have loose snow will actually be more concerning.  Be on the lookout for smooth denser snow.  In popular areas, look for clues of recent wind transport such as previous ski tracks being covered over by blown snow.  It will be important to do your own localized assessments before committing to steep terrain to determine if the windslabs you encounter are old and stable or new and sensitive.  Also if traveling near ridges, beware of cornices that could fail under your feet and lead to a bad fall.    

advisory discussion

We’ve come to the end of one of our few small high-pressure windows of the season so far.  3-4 days of sunshine, calm winds and mild temperatures have persisted from Tuesday through yesterday (Friday) morning, giving us all a needed break from storms and a reminder about why we all love California!  The latest storm on Monday dropped 1-7" of new snow (with greater amounts near Mammoth and June), and lots of wind out of the SW.  This left some great powder skiing in sheltered locations, and a wide variety of wind-affected snow including wind slabs of varying densities from soft to very hard.  The following 3-4 calm days gave these wind slabs a chance to heal, but small loose-wet point releases starting near rock-bands on solar aspects became a small issue as slopes warmed.  Yesterday about noon, winds begin to increase substantially ahead of the next moderate storm that will bring a short intense dump of snowfall beginning tonight (Saturday) thru Sunday morning.  Today these SW winds will increase even more, with gusts expected into the 120mph range over ridgetops, and into the 40mph range at 8000’.  New small isolated wind slabs may form as a result of these winds ahead of the new snowfall in the rare exposed areas that still have loose snow available for transport and where the winds don’t just blow this limited loose snow into the atmosphere.  Despite the partly to mostly sunny skies today, the strong winds and slightly cooler temperatures should eliminate any issues of wet-loose instability. 

weather

A winter storm warning is in effect from 10pm tonight until 10pm Sunday night for areas north of Rock Creek.  High wind advisory is in effect until 10pm Sunday throughout the entire forecast region, including Bishop and south.  The most intense snowfall is expected from 10pm tonight until 6am Sunday.

Today (Saturday) will be a windy day as pre-frontal winds that began yesterday continue to increase out of the SW into the 120mph range over high elevation ridgetops, and into the 40mph range below 8000’.  Expect partly cloudy skies with high temperatures reaching the upper 30s near 10,000’.  Snow showers could begin this afternoon, with little accumulation expected before temperatures begin to plummet and the real dump of snow begins late tonight thru early Sunday morning.

Expect a cold windy snowy day Sunday.  For Mammoth and north, 1-2ft+ of total accumulation is expected to occur by mid-morning, with only a few inches expected south of Rock Creek thru the mountains outside of Bishop.  Continued convective snow showers through the day will bring greater amounts of accumulation in favored localized areas.  Temperatures will continue to fall throughout the day dropping into the single digits by late afternoon around 10,000’.  Strong SW winds will continue with gusts over 100mph above 10,000’.   

Beginning Monday, high pressure returns for the week with mostly sunny skies and slightly above average temperatures.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Partly cloudy. Slight chance of snow in the afternoon. Mostly cloudy. Chance of snow. Cloudy. Snow.
Temperatures: 35 to 45 deg. F. 21 to 29 deg. F. 23 to 33 deg. F.
Wind direction: SW SW SW
Wind speed: 20 to 30 mph. Gusts up to 65 mph increasing to 75 mph in the afternoon. 20 to 35 mph with gusts to 90 mph. 25 to 35 mph with gusts to 70 mph.
Expected snowfall: 0 in. 5 to 10 in. 8 to 16 in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Partly cloudy. Mostly cloudy. Chance of snow in the evening. Snow likely after midnight. Cloudy. Snow.
Temperatures: 27 to 37 deg. F. 15 to 21 deg. F. 18 to 24 deg. F.
Wind direction: SW SW SW
Wind speed: 30 to 35 mph with gusts to 80 mph. 40 to 60 mph with gusts to 100 mph. 35 to 55 mph with gusts to 100 mph.
Expected snowfall: 0 in. 5 to 10 in. 8 to 16 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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