Eastern Sierra Avalanche Advisory - 3/31/17

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THIS AVALANCHE ADVISORY EXPIRED ON April 1, 2017 @ 6:58 am
Avalanche Advisory published on March 31, 2017 @ 6:58 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
bottom line

With up to 6+” of new snow in some areas (such as around Mammoth) in the last 24 hours and moderate N winds today (shifted from very strong out of the SW yesterday morning), isolated areas of new wind slab sensitive to human triggering will be the greatest avalanche concern today in areas that received more than a few inches of new snow.  If the sun comes out this afternoon, southerly and westerly facing slopes with new snow could have the potential for small loose-wet natural slides.  Evaluate snow and terrain carefully and identify areas of concern.  Beware of firm conditions in areas that did not receive much new snow where a fall could result in a slide-for-life.     

How to read the advisory

Bottom Line

With up to 6+” of new snow in some areas (such as around Mammoth) in the last 24 hours and moderate N winds today (shifted from very strong out of the SW yesterday morning), isolated areas of new wind slab sensitive to human triggering will be the greatest avalanche concern today in areas that received more than a few inches of new snow.  If the sun comes out this afternoon, southerly and westerly facing slopes with new snow could have the potential for small loose-wet natural slides.  Evaluate snow and terrain carefully and identify areas of concern.  Beware of firm conditions in areas that did not receive much new snow where a fall could result in a slide-for-life.     

Avalanche Problem 1: Wind Slab
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Strong SW winds blew yesterday morning at all elevations, with gusts well over 100mph at upper elevations.  These winds lightened to moderate levels and shifted out of the North late yesterday morning, and will continue that way today.  In areas that received more than a few inches of new precipitation since yesterday morning (such as around Mammoth), new wind slabs sensitive to human triggering likely have formed on the leeward side of ridges, across slopes and gullies, and around other features that promote drifting.  Be aware that the winds shifted directions dramatically yesterday afternoon, so all aspects could be suspect.  Be on the lookout for areas with new denser snow and watch for signs such as cracks shooting from your skis to let you know that steep slopes should be approached with caution and wind-loaded slopes avoided.

Avalanche Problem 2: Loose Wet
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Cool temperatures, continued winds, and cloudy skies will slow the melting process today on most slopes.  However, southerly to westerly facing steep slopes with more than a few inches of new cold snow that do receive some sunshine this afternoon could be suspect for rapid warming, and have the potential for small loose wet natural avalanches.  While these are likely to be small, their dense nature could knock a person over and carry them into undesirable terrain.  Slope warming will be intensified around rock outcrops.    

advisory discussion

We have fallen into a springtime pattern this month with periods of fast windy storms hitting our area followed by periods of clearing and sunshine.  Avalanche concern has been shifting back and forth between concern over new sensitive wind slabs as we receive new snow and wind, to loose-wet avalanches as the sun comes back out and temperatures rise.  We are now in a transition day as the latest storm which dropped between 2-6+” of new snow yesterday is leaving our area, allowing winds to begin to decrease, before sunshine is expected tomorrow.  Along with avalanche concern, very firm conditions exist either where the wind has swept slopes or where slopes are re-frozen from previous days’ melting.  Falls in many places could result in a slide for life. 

recent observations
  1. New Snow since yesterday morning (as of 5am this morning)
  2. -Va Lakes Ridge (9,445’):          ~3”
  3. -June Mtn (9,148’):                   2.5”
  4. -Mammoth Sesame (9,014’):      6” (0.4” H2O)
  5. -Rock Creek (9,600’):                ~2.5”
  6. -Sawmill near Bigpine (10,200’): ~1”

-3/29 - Convict area: Signs of loose-wet activity, weather 

-3/29 - Swall Meadows: Spring transitional snow

-3/28 - Convict: Spring snow conditions

-3/28 - Mammoth - Sherwins: Stable conditions

-3/27 - June: firm conditions, slow not-so-transitional day

-3/27 - Lee Vining: Some touchy windslab, spring transition

weather

Our spring-time pattern continues with brief low accumulation storms and high winds followed by periods of clearing and sunny skies.

Friday:  Expect brisk north winds with gusts reaching up to 85mph over ridgetops this morning and cloudy skies as the latest spring storm exits the area leading to diminished clouds and slightly calmer winds in the afternoon. An inch of new accumulation since last night is possible.  Below average temperatures should reach the low 30s around 10,000’. 

Saturday:  Sunny skies return with temperatures creeping into the upper 30s around 10,000’, and decreasing northeast winds with gusts into the 40s over ridgetops.

Long-term:  A brief weak shortwave is expected to brush across the region Sunday night into Monday morning bringing some snow flurries with no real accumulation expected.  A brief high pressure ridge bringing dry conditions returns thru mid week, before yet another fast short wave disturbance breaks it down leading the way for more pacific moisture and another possible Atmospheric River by weeks-end. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Isolated snow showers in the morning. Clear. Sunny.
Temperatures: 32 to 38 deg. F. 20 to 25 deg. F. 40 to 45 deg. F.
Wind direction: N N NE
Wind speed: 20 to 30 mph decreasing to 15 to 20 mph in the afternoon. Gusts up to 60 mph. 15 to 25 mph. Gusts up to 45 mph decreasing to 35 mph after midnight. Light winds becoming northeast 10 to 15 mph in the afternoon. Gusts up to 30 mph.
Expected snowfall: up to 1 in. 0 in. 0 in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy then becoming partly cloudy. Isolated snow showers in the morning. Clear. Sunny.
Temperatures: 28 to 35 deg. F. 18 to 23 deg. F. 37 to 42 deg. F.
Wind direction: N N NE
Wind speed: 30 to 50 mph with gusts to 85 mph. 20 to 35 mph with gusts to 60 mph. 20 to 30 mph with gusts to 45 mph decreasing to 15 to 20 mph with gusts to 30 mph in the afternoon.
Expected snowfall: up to 1 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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