Eastern Sierra Avalanche Advisory - 3/18/17

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THIS AVALANCHE ADVISORY EXPIRED ON March 19, 2017 @ 5:49 am
Avalanche Advisory published on March 18, 2017 @ 5:49 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center
bottom line

Spring like conditions will continue to dominate Sunday with the surface snow warming through the day (Easterly > Southerly > Westerly), natural and human triggered small loose wet avalanches possible as the snow surface softens. An approaching storm system increased cloud cover overnight keeping temperatures warm & mild overnight, which has produced a weak freeze with the surface snow likely becoming unsupportable fairly quickly despite brisk winds and cloud cover in the mid to upper elevations.  Caution - small wet slides are dense/heavy and are capable of carrying a rider into hazardous terrain or possibly entrain enough snow to bury a person, especially if a terrain trap is involved.  Early starts are recommended before the snow become saturated and unsupportable.  Caution – Cornices can fail unexpectedly, avoid Corniced slopes and give them wide berth while traveling along ridgelines. Possible “Slide for Life” conditions exist in the AM before the snow surface thaws. Evaluate snow and terrain carefully. 

How to read the advisory

Bottom Line

Spring like conditions will continue to dominate Sunday with the surface snow warming through the day (Easterly > Southerly > Westerly), natural and human triggered small loose wet avalanches possible as the snow surface softens. An approaching storm system increased cloud cover overnight keeping temperatures warm & mild overnight, which has produced a weak freeze with the surface snow likely becoming unsupportable fairly quickly despite brisk winds and cloud cover in the mid to upper elevations.  Caution - small wet slides are dense/heavy and are capable of carrying a rider into hazardous terrain or possibly entrain enough snow to bury a person, especially if a terrain trap is involved.  Early starts are recommended before the snow become saturated and unsupportable.  Caution – Cornices can fail unexpectedly, avoid Corniced slopes and give them wide berth while traveling along ridgelines. Possible “Slide for Life” conditions exist in the AM before the snow surface thaws. Evaluate snow and terrain carefully. 

Avalanche Problem 1: Loose Wet
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As slopes warm, soften, and become wet throughout the day, natural and human triggered small loose wet avalanches will become increasingly possible as the snow surface thaws and becomes wet during the day. An approaching storm system will increase cloud cover with accompanying moderate to strong SW winds will reduce and slow surface snow thawing in the mid and upper elevations.  Cloudy skies overnight has kept temperatures warm & mild overnight, which has produced a weak freeze with the surface snow likely becoming unsupportable fairly quickly despite brisk winds and cloud cover. The surface snow will warm through the day (Easterly > Southerly > Westerly), increasing near cliffs and rock outcrops. Natural and human triggered small loose wet avalanches possible as the snow surface softens. Large pinwheels or snow penetration boot top or greater are signs the snow is loosing strength and becoming unstable, steep terrain on these aspects should be avoided.   

A number of factors affect the rate of snow thawing: Aspect (Easterly facing slopes begin to thaw first, followed by south and then west in the afternoon); Elevation: lower elevations warm more quickly than higher elevation, Cloud cover: cloud cover can shade the slopes slowing thawing. However, clouds can help to slow or limit overnight cooling limiting how solid the snow sets-up. Thin cloud cover during the day can trap the heating from the sun filtering through producing strong warming, Air temperature: Warmer air temperatures leads to more rapid snowpack warming.  

advisory discussion

The last snowfall we received was almost 2 weeks ago on March 5th, and since then spring conditions have dominated our area with above average temperatures and lots of sunshine.  Loose-wet avalanches have been and will continue to be the main, if not only, avalanche concern for a few more days until the weather changes and the next winter storm impacts our area early next week.  The past two weeks have been a big window of opportunity for many to explore the high alpine peaks and hunt for some good corn skiing if one times aspect and elevation and right.  This hasn’t been always easy with the variable cloud cover and winds which we have been receiving which effect how the snow softens.  In terms of mountain hazards, very firm conditions have been an even greater concern than avalanches lately.  The last snowfall almost 2 weeks ago was accompanied by very high winds, and much of the alpine was left highly wind-effected and firm.  Frozen slopes before they soften and areas with hard smooth wind board threaten slide-for-life conditions.  Crampons, ice axes, whippets, and most importantly good judgement, are all essential for venturing into the alpine.  Warm days and softening snow also leads to greater threat for cornice failures, either naturally or from someone's weight on top of one.  Pay close attention if you are travelling along ridgelines to give edges of slopes that could be corniced a wide berth, and avoid being under cornices especially as the day warms.   

weather

Some weak cold storm fronts in the Pacific Northwest this weekend will try unsuccessfully to move south to our area, resulting in increased winds and clouds for us in the Sierra.

Today (Saturday) well above average temperatures will continue with highs again reaching the upper 40s around 10,000’.  Clouds are expected to increase throughout the day becoming mostly cloudy by afternoon.  Southwest winds will be on the increase as well with gusts reaching 80mph above 10,000’ by early afternoon, before decreasing later in the afternoon.  

For tomorrow (Sunday) expect similar warm temperatures and winds and mostly cloudy skies with a possible flurry or two in the afternoon. 

Long Term:  Our spring conditions will be ending early next week as a more active weather pattern moves in bringing much cooler temperatures and several waves of snow showers beginning on Monday night into Tuesday, Thursday and possibly thru the end on the week.

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 then becoming mostly cloudy. Mostly cloudy. Mostly cloudy. Slight chance of showers in the afternoon.
Temperatures: 48 to 56 deg. F. 28 to 34 deg. F. 46 to 54 deg. F.
Wind direction: SW SW SW
Wind speed: 15 to 25 mph. Gusts up to 45 mph. 15 to 25 mph with gusts to 45 mph. 15 to 20 mph. Gusts up to 45 mph.
Expected snowfall: 0 in. 0 in. trace in.
Over 10,000 ft.
  Saturday Saturday Night Sunday
Weather: Partly cloudy then becoming mostly cloudy. Mostly cloudy. Mostly cloudy. Slight chance of showers in the afternoon.
Temperatures: 41 to 49 deg. F. 22 to 28 deg. F. 40 to 48 deg. F.
Wind direction: SW SW S
Wind speed: 35 to 55 mph decreasing to 30 to 45 mph in the afternoon. Gusts up to 80 mph. 30 to 50 mph with gusts to 75 mph. 30 to 50 mph with gusts to 90 mph.
Expected snowfall: 0 in. 0 in. trace 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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