Eastern Sierra Avalanche Advisory - 3/27/17

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

THIS AVALANCHE ADVISORY EXPIRED ON March 29, 2017 @ 6:27 am
Avalanche Advisory published on March 27, 2017 @ 6:27 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center
bottom line

As of 5AM Monday morning, there are between 1 and 3 inches of new snow in the eastern Sierra, primarily north of Mammoth and at elevations above 7,000’. Southwest winds accompanied this fast moving storm and they will shift more to the north tonight (Monday) and Tuesday as temperatures rebound. Wind slabs will be our primary avalanche concern today at middle and upper elevations. As temperatures climb this afternoon and tomorrow, so will the risk of loose wet avalanches on solar slopes at middle and lower elevations. Natural avalanches will be unlikely, but human triggered avalanches possible. Evaluate the snowpack and terrain carefully to identify features of concern.

How to read the advisory

Bottom Line

As of 5AM Monday morning, there are between 1 and 3 inches of new snow in the eastern Sierra, primarily north of Mammoth and at elevations above 7,000’. Southwest winds accompanied this fast moving storm and they will shift more to the north tonight (Monday) and Tuesday as temperatures rebound. Wind slabs will be our primary avalanche concern today at middle and upper elevations. As temperatures climb this afternoon and tomorrow, so will the risk of loose wet avalanches on solar slopes at middle and lower elevations. Natural avalanches will be unlikely, but human triggered avalanches possible. Evaluate the snowpack and terrain carefully to identify features of concern.

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

Moderate winds from the southwest yesterday and last night (Sunday), coupled with 1-3 inches of snow, deposited small, but potentially sensitive wind slabs on northwest to northeast to southeast aspects over the Sierra crest. Winds will shift predominately to the north by Monday night and may transport some of the remaining snow onto southerly aspects, especially above about 10,000’. Heightened avalanche conditions will linger on specific wind loaded terrain at upper and middle elevations through the forecast period. Expect to see wind loading just below ridges, on cross loaded slopes, and on the leeward sides of convexities. Be wary of hollow, drum-like sounding snow or cracks shooting out from your feet.

Avalanche Problem 2: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Showers will exit the region today as a brief warming trend begins. This afternoon and into Tuesday temperatures will rebound as low pressure moves out of the area. As the snow surface warms quickly to its melting point, especially around rock outcrops, below cliff bands, and in open bowls throughout the day, loose wet avalanches will again be a problem. Time of day is critical with east aspects receiving the first radiation of the day, then south, then west. Lower elevations will warm more quickly than higher elevations. Watch out for pinwheels rolling down the slopes around and above you. Even small point releases are heavy and can be hard to escape. They could knock you down or carry you into dangerous terrain.

advisory discussion

Fast moving spring showers, dropping between 1 and 12+ inches of snow, have been affecting our area for the past week. These storms have come with moderate to strong southwest winds that transport much of that new snow onto leeward slopes and pack it into dense wind slabs. In the hours and days between, warm temperatures and sunshine have been returning to heat the new snow and cause wet point releases near rocky areas and in steep terrain. One such cycle played out this past weekend. Wind slabs deposited during Friday’s storm released from artificial triggers throughout Saturday. Mammoth Mountain Ski Patrol had widespread results from avalanche control work and skier-cut cornice drops on the Mammoth Crest produced several large slides. Loose dry avalanches were also widespread Saturday morning in steep areas that had received the most new snow. But, temperatures warmed significantly Saturday afternoon, and, as is typical for spring, loose wet avalanches quickly became a problem at middle and lower elevations.

Sunday, moderate southwest winds began to blow again ushering in the next quick moving front across the Sierra. This latest storm has already left 1 to 3 inches of snow as of early Monday morning, primarily in the northern half of the forecast zone. This combination will create wind slabs on steep, middle and upper elevation slopes and features that promote drifting and loading. Showers will exit the region today (Monday) and we can expect winds to shift more to the north tonight and Tuesday when temperatures will rebound. With increased sunshine and higher temps this afternoon and Tuesday, loose wet avalanches will become increasing likely at lower and middle elevations. Large pinwheels or ski penetration of boot top or greater are signs the snow is loosing strength and becoming unstable. Pay attention as you travel, notice conditions changing and trends. Perform your own stability tests and identify potentially hazardous terrain.

weather

This current storm will continue to bring precipitation to the Sierra through Monday morning. The bulk of the precipitation will push through before 5am Monday with only light residual showers expected through mid morning. Brisk and drier northwest flow behind the cold front Monday will clear out much of the residual shower activity for the Sierra with gusty northwest winds.

Northeast flow on Tuesday along with shortwave ridging will allow for a modest warm up for the region with temperatures in the mid 40s to low 50s. Tuesday through Wednesday will also feature light winds with strong ridge top gusts and dry conditions before another storm approaches the area.

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: Partly cloudy. Partly cloudy. Sunny.
Temperatures: 32-38 deg. F. 18-23 deg. F. 41-46 deg. F.
Wind direction: W N N
Wind speed: 10 to 15 mph with gusts to 40 mph. 15 to 25 mph. Gusts up to 65 mph decreasing to 55 mph after midnight. 10 to 15 mph with gusts to 60 mph.
Expected snowfall: 60% probability...no accumulation. 40% probability...1 to 3 in. 80% probability...no accumulation. 20% probability...up to 1 in. 0 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: Partly cloudy. Slight chance of snow showers in the afternoon. Partly cloudy. Slight chance of snow showers in the evening. Sunny.
Temperatures: 25-33 deg. F. 13-19 deg. F. 37-43 deg. F.
Wind direction: W N N
Wind speed: 20 to 30 mph. Gusts up to 60 mph decreasing to 40 mph in the afternoon. 25 to 40 mph with gusts to 65 mph. 30 to 45 mph with gusts to 70 mph decreasing to 25 to 35 mph with gusts to 60 mph in the afternoon.
Expected snowfall: 60% probability...no accumulation. 40% probability...1 to 4 in. 80% probability...no accumulation. 20% probability...up to 2 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.

ESAC receives support from ...