Eastern Sierra Snowpack Summary - 2016-02-15 06:55

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THIS ADVISORY EXPIRED ON February 17, 2016 @ 6:55 am
Avalanche Advisory published on February 15, 2016 @ 6:55 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
Avalanche Character 1: Loose Wet
Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Solar aspects that receive more direct sunlight include E-SE-S-SW facing slopes.  Indicators that these slopes are becoming overly warm and potentially unstable include the start of rollerball activity and wet point releases (often initiating near rockbands) and the snow no longer being able to support the weight of a skier or boarder (sinking in up to and past boot top.)  Cloud cover, wind, air temperature and time of day are all variables that will effect how much and when these slopes soften.  Safety and good riding conditions (not quite corn, but smooth and creamy) on these aspects is all about timing it right.  While wet point releases in and of themselves are likely to be small and relatively slow moving, they could knock a person off balance.  As a wet slide entrains more and more snow, they are like flowing concrete, making it very difficult for a rider to get out of once caught.  These can be particularly dangerous if the flow ends in a terrain trap or even a less steep slope where even a small amount of snow could result in a deep enough pile up to bury a person. 

Avalanche Character 2: 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.

While very isolated and rare, small sensitive windslabs may be found in steep alpine terrain that could knock a skier or rider off balance.  Always be on the lookout for these small pockets, especially when riding steep technical exposed lines where a fall could have bad consequences.   

Snowpack Discussion

Our June-uary thaw has been in February this year.  High pressure, well above average temperatures, and mostly sunny skies and no new snow have prevailed for the past 2 weeks, and will continue through Tuesday this week.  These weather conditions have given the snowpack a good deal of time to settle and stabilize.  Normal caution should still be taken, with emphasis on considering a couple of key points:  1) Avoid overly warming steep solar aspects (E-SE-S-SW), and 2) Keep an eye out for the very isolated rare small sensitive windslab that may be found in steep alpine terrain that could knock one of balance.  

Solar aspects that receive more direct sunlight include E-SE-S-SW facing slopes.  Indicators that these slopes are becoming overly warm and potentially unstable include the start of rollerball activity and wet point releases (often initiating near rockbands) and the snow no longer being able to support the weight of a skier or boarder (sinking in up to and past boot top.)  Cloud cover, wind, air temperature and time of day are all variables that will effect how much and when these slopes soften.  The clearer the skies, the calmer the winds, and the warmer the air temperature, the earlier these solar exposed slopes will soften, and the more potential they have for a wet slide to occur with consequence.  Safety and good riding conditions (not quite corn, but smooth and creamy) on these aspects is all about timing it right.  While wet point releases in and of themselves are likely to be small and relatively slow moving, they could knock a person off balance.  Small wet slides can entrain more and more snow as they move down hill and can be like concrete flows, making it very difficult for a rider to get out of once caught.  These can be particularly dangerous if the flow ends in a terrain trap or even a less steep slope where even a small amount of snow could result in a deep enough pile up to bury a person.  More direct southerly facing features such as steep gullies and bowls at mid elevations are the most likely place where these wet-slides could possibly be triggered by a human, and can potentially even still occur naturally.   

Besides avalanche concerns, be aware of the slide-for-life potential that exists on steep slopes that are firm and frozen if one were to loose an edge, on the up as well as the down.          

Clear skies at night should continue to allow a good refreeze of these solar aspects, even as night time lows increase to just above freezing at lower to mid elevations on Monday and Tuesday night.  Above average temperatures, clear skies and light winds during the day should keep this spring-like cycle of skiing going for Monday and Tuesday.  Beware of overly warming slopes as mentioned above starting late morning and into the afternoon.  Clouds, higher winds, and cooler temperatures move in Wednesday as the high-pressure ridge breaks down and a Pacific winter storm moves into our region ending our mid-winter thaw.  Snowfall and wind Wednesday night, depending on amounts, will bring heightened avalanche concerns for Thursday.  

recent observations

Observations throughout the region this past week on northerly facing slopes (NE-N-NW) above 8000’ have consistently shown a stable snowpack. 

Observers Sunday (2-14) in the McGee Creek – Baldwin Cirque area ~10,500ft noted wet point-release / rollerballs coming down southerly facing chutes today.

Observations in the Sherwins Sunday (2-14) revealed due east facing slopes at 9,800’ undergoing surface melt-freeze.  Northerly facing slopes up to ~8600’ were showing 2-3cm surface melt by 1pm. 

Observations in the Convict area on Saturday (2-13) on E to SE facing slopes between 12,200’ and 10,200’ showed surface softening in the very acceptable range between 11-11:45am.  This day had early morning thin clouds covering sun until about 9am, then clear skies, and calm winds. 

weather

High pressure will remain in the Sierra through Tuesday, keeping our region dry with well above average temperatures and mostly clear skies.  For Monday, expect sunny skies, highs in the mountains from the mid 40s to mid 50s, light to moderate north winds from 15-25mph, gusting into the 30s and 40s.  Tuesday should be similar, except for the winds are expected out of the southwest.  Tides will change Wednesday, as an approaching pacific storm will put an end, at least for a while, to our spring conditions.  This quick moving storm is expected to bring 1-2” of water Wednesday night (up to a foot+ of snow at higher elevations), with strong SW winds, highs in the upper 30s Wednesday, and upper 20s on Thursday.  Snow levels are expected to begin around 7500', and drop to around 4500' by Thursday morning.       

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: SUNNY CLEAR SUNNY
Temperatures: 50S deg. F. UPPER 20S TO MID 30S deg. F. MID 50S TO LOW 60S deg. F.
Wind direction: NORTH NORTHEAST SOUTHWEST IN THE AFTERNOON
Wind speed: 15 - 20 MPH, GUSTS UP TO 35, DECREASING TO 25 IN THE AFTERNOON 10 - 15 MPH 10 - 15 MPH, GUSTING TO 25 IN THE AFTERNOON
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Monday Monday Night Tuesday
Weather: SUNNY CLEAR SUNNY
Temperatures: MID 40S TO LOW 50S deg. F. MID 20S TO LOW 30S deg. F. MID 40S TO MID 50S deg. F.
Wind direction: NORTH NORTH SOUTHWEST
Wind speed: 15 - 25 MPH, GUSTS TO 40 DECREASING TO 30 MPH IN THE AFTERNOON 10 - 15 MPH WITH GUSTS TO 25 10 - 15 MPH, GUSTS TO 25 IN THE AFTERNOON
Expected snowfall: 0 in. 0 in. 0 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.

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