Eastern Sierra Snowpack Summary - Mar 21 2016

The backcountry is more accessible than it has been in years. Please help!  ... Click Here to Find Out How

THIS ADVISORY EXPIRED ON March 23, 2016 @ 7:00 am
Avalanche Advisory published on March 21, 2016 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Southwest winds began increasing yesterday, and will peak this afternoon in the 60-70 mph range with gusts reaching 110 over ridgetops.  Cloud cover has increased as well, and a chance of some light snowfall exists for this afternoon and tomorrow, with the potential for 1-6” of snow tonight (Monday) at upper elevations.  Avalanche concern over fresh new windslabs will increase today (Monday) as these high winds transport some existing loose snow.  Avalanche concern over fresh windslabs will rise dramatically tonight and tomorrow if we receive more than a couple inches of new snow tonight.  A couple + inches of snow with strong winds could mean the development of dangerous fresh sensitive windslabs 1-2ft thick.  These will likely form on NW-N-NE-E-SE facing slopes below ridgelines (the intensity of the winds will likely lead these slabs to form lower down from ridgelines than normal), sidewalls of gullies, and across slopes at all elevations.  The faceted snow surface on more northerly facing slopes and the firm frozen melt-freeze crusts that exist on solar aspects will likely make these new windslabs even more sensitive.  For today (Monday) small human triggered avalanches may be possible in isolated areas at upper elevations.  For Tomorrow (Tuesday), natural avalanches may be possible and human triggered avalanches very likely if new snowfall a

Snowpack Discussion

Cloud cover, high winds and cooling temperatures will put a halt to loose-wet avalanche concerns for Monday and Tuesday.  As a replacement, avalanche concern for fresh sensitive windslabs will increase as high SW winds and the potential for several inches of new snow fall tonight (Monday) will potentially form new fresh windslabs on NW-N-NE-E-SE facing slopes at mid to upper elevations.

Warm temperatures, calm winds, and mostly sunny skies over the past week have led to spring-like skiing and riding conditions along with spring-like avalanche concern over loose-wet releases on solar aspects (E-SE-S-SE-W).  Clear skies have kept the nightly re-freeze of snow surfaces strong, and the daily warming on solar aspects at mid to upper elevations has led to some good corn snow development.  Some signs of rollerball and small wet-point releases have been noted, along with isolated small wet slab releases in shallow terraced areas. 

Northerly aspects (NE-N-NW), except for lower elevations below 9500’, have remained fairly cold and wintery.  Windslabs that developed over a week ago have shown to have settled and bonded well.  The clear skies and cool night time temperatures at mid to upper elevations have led to faceting of snow surfaces, resulting in the softening of some of the firm northerly facing snow surfaces, allowing for the return of pleasant skiing and riding conditions on these aspects.    

This will all change for the next two days (Monday and Tuesday) as a low-pressure system moves in off of the coast.  Southwest winds began increasing yesterday, and will peak this afternoon in the 60-70 mph range with gusts reaching 110 over ridgetops.  Cloud cover has increased as well, and a chance of some light snowfall exists for this afternoon and tomorrow, with the potential for 1-6” of snow tonight (Monday) at upper elevations.  Temperatures have also begun to drop significantly, with highs expected in the mid to upper 30s at mid-mountain elevations today, and 10 degrees colder on Tuesday.  This weather change will put a halt to loose-wet avalanche concerns through Tuesday.  Avalanche concern over fresh new windslabs will increase today (Monday) as these high winds transport some existing loose snow.  Avalanche concern over fresh windslabs will rise dramatically tonight and tomorrow if we receive more than a couple inches of new snow tonight.  A couple + inches of snow with strong winds could mean the development of dangerous fresh sensitive windslabs 1-2ft thick.  These will likely form on NW-N-NE-E-SE facing slopes below ridgelines (the intensity of the winds will likely lead these slabs to form lower down from ridgelines than normal), sidewalls of gullies, and across slopes at all elevations.  The faceted snow surface on more northerly facing slopes and the firm frozen melt-freeze crusts that exist on solar aspects will likely make these new windslabs even more sensitive.  For today (Monday) small human triggered avalanches may be possible in isolated areas at upper elevations.  For Tomorrow (Tuesday), natural avalanches may be possible and human triggered avalanches very likely if new snowfall amounts tonight exceed a couple of inches.     

For Wednesday, high pressure will return bringing sunny skies, warmer temperatures and calmer winds.  This will bring a return to loose-wet avalanche concern, especially with new snow on the ground, and concern over fresh windslabs will continue to exist as well before they have the time to settle and stabilize. 

recent observations

Observations made in the VA lakes area over the past couple of days have shown limited snow surface softening and melt above 11,000’ on SE and E facing slopes due to the presence of high cloud cover on Saturday and a mix of thin high cloud cover and moderate winds on Sunday, despite warm temperatures.  Below 11,000 snow surfaces were softening and melting to greater extents as a function of lower elevation and more southerly aspect.  Very limited rollerball and loose wet point release activity.

Observations in the Mammoth Lakes Basin and Crest yesterday revealed mostly blue skies and full sunshine and moderate SW winds at mid to upper elevations, with some visible snow transport at upper elevations.  Hand-pit tests across upper elevation slopes in areas with windslab resulted in variable shears, some rough, come clean and planar from 15-30cm deep, all with moderate to hard force.  These were presumably all old windslabs that developed before the calm period over the last several days.  No new sensitive windslabs were detected even in areas with this current snow transport.  Thin surface melt and refreeze was occurring on ENE aspects up to atleast 10,500’.   SW aspects at ridgetop elevations (11,200’) were moist and corny at 3pm, with shallow ski penetration and ~8cm boot penetration.  Limited signs of new rollerball / loose wet point releases, and these were limited to steep lower elevation slopes (9500’) with southerly aspect originating around cliff bands.

Observations in the Convict Lake area, Old Man’s Bowl revealed surface softening / melting and corn skiing on aspects south of East, and north of East surfaces remained cold and variable.  No reports of significant rollerball / wet-loose point release activity.

weather

 

A long pressure system is moving across Northern California from the coast.  While the brunt of this system will remain north of our region, we will see significant winds, cloudy skies, and the possibility of some snowfall, before high pressure returns Tuesday evening and remains with us through the rest of the week.

For today (Monday) expect mostly cloudy skies, cooler temperatures in 30s at 10,000’, and most notably high SW winds peaking this afternoon in the 60-70 mph range, with gusts over 100mph over ridgetops.  There is a chance of light precipitation this afternoon, with less than an inch of snow possible at mid to upper elevations, and drizzle lower down. 

Tonight, temperatures will drop significantly with lows in the teens at 10,000’, winds will stay strong out of the SW, and up to 6” of new snowfall maybe possible at mid to upper elevations. 

Tomorrow (Tuesday), temperatures will be 10 degrees cooler than today with highs in the 20s at 10,000’, light scattered snow showers will linger with little accumulation expected, and winds will shift out of the West and decrease into the moderate range by the afternoon with ridgetop gusts expected to decrease into the 50 mph range.      

High pressure is expected to return for the remainder of the week after Tuesday, bringing clear skies, warming temperatures and decreased winds.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Monday Monday Night Tuesday
Weather: MOSTLY CLOUDY. CHANCE OF SNOW IN THE AFTERNOON. PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. CHANCE OF SNOW IN THE EVENING...THEN SNOW AFTER MIDNIGHT. PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE MORNING...THEN SCATTERED SNOW SHOWERS IN THE AFTERNOON.
Temperatures: HIGHS IN THE UPPER 30 TO UPPER 40S deg. F. LOWS IN THE LOW TO UPPER 20S deg. F. HIGHS IN THE UPPER 20S TO UPPER 30S deg. F.
Wind direction: SOUTHWEST SOUTHWEST WEST
Wind speed: 35 TO 50 MPH WITH GUSTS TO 70 MPH. 40 TO 55 MPH WITH GUSTS UP TO 85 MPH DECREASING TO 25 TO 40 MPH WITH GUSTS TO 60 MPH AFTER MIDNIGHT. 20 TO 40 MPH WITH GUSTS TO 60 MPH DECREASING TO 15 TO 25 MPH WITH GUSTS TO 40 MPH IN THE AFTERNOON.
Expected snowfall: UP TO 1 in. 1 - 4 in. UP TO 1 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: MOSTLY CLOUDY. CHANCE OF SNOW IN THE AFTERNOON. PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. SNOW. PARTLY CLOUDY THEN BECOMING MOSTLY CLOUDY. SCATTERED SNOW SHOWERS.
Temperatures: HIGHS IN THE LOW TO MID 30S deg. F. LOWS IN THE LOW TO UPPER TEENS deg. F. HIGHS IN THE LOW TO UPPER 20S deg. F.
Wind direction: SOUTHWEST SOUTHWEST WEST
Wind speed: 50 TO 65 MPH WITH GUSTS TO 100 MPH INCREASING TO 60 TO 75 MPH WITH GUSTS TO 110 MPH IN THE AFTERNOON. 55 TO 70 MPH WITH GUSTS TO 105 MPH DECREASING TO 40 TO 55 MPH WITH GUSTS TO 80 MPH AFTER MIDNIGHT. 40 TO 55 MPH WITH GUSTS TO 75 MPH DECREASING TO 20 TO 35 MPH WITH GUSTS TO 50 MPH IN THE AFTERNOON.
Expected snowfall: UP TO 1 in. 2 TO 6 in. UP TO 1 in.
Disclaimer

This snowpack summary applies only to backcountry areas outside established ski area boundaries. This snowpack summary only describes general avalanche conditions and local variations always occur. This snowpack summary expires 24 hours after the posted time unless otherwise noted. The information in this snowpack summary is provided by the Eastern Sierra Avalanche Center who is solely responsible for its content.

ESAC receives support from ...