Avalanche Advisory: Tuesday - Mar 20, 2018

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THIS AVALANCHE ADVISORY EXPIRED ON March 21, 2018 @ 6:59 am
Avalanche Advisory published on March 20, 2018 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

LOW avalanche danger will persist through today.  Light snow showers this afternoon accompanied by moderate SW winds could lead to small wind slab formation at upper elevations by evening resulting in an increase to MODERATE avalanche danger tonight once areas receive more than a few inches of new snow.   

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Wind Slab
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
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    Small

Light snow fall is expected to start early afternoon, and light SW winds are expected to begin increasing this evening and more considerably tonight with gusts up to 80mph at upper elevations after midnight.  Sensitive new wind slabs at treeline and above will likely form just below ridges on NW-NE-SE slopes, in the sidewalls of gullies and around other features that promote drifting.  This concern will develop for areas once they receive more than a few inches of new snow, which won’t likely be until tonight.  Be on the lookout especially late in the day for fresh denser wind deposits, and signs such as shooting cracks indicating the potential for unstable snow and that caution should be used around steep wind-loaded slopes. 

advisory discussion

4 days have now passed since the last significant snowfall.  The last storm dropped 20-30” of new snow between 3/13-16 for most of the forecast region, except for the southern reaches outside of Bishop where the mountains received closer to a foot.  Snow sensors are showing that this new snow has now settled to about 2/3 of that total amount.  While evidence of widespread natural avalanche activity occurring during the last storm has been reported, no signs of current instablities have been reported over the last several days except for some very minor small loose wet point releases.  Tests on the mid-storm graupel layers that were found around the June area have been shown to be stabilizing.  

With today’s cloudy skies and light snowfall expected to begin this afternoon, instabilities of all sorts should remain low through today unless new snowfall amounts far exceed expectations.  At elevations below 9000', some slope warming will likely occur on all aspects due to warm temperatures and cloud cover and light drizzle.  Precipitation amounts are expected to be quite light today, so rain on snow instability concerns should not develop.  In addition to wind slabs, storm slabs could become a very isolated concern late tonight for sheltered steep slopes that receive more than a half a foot of new snow, but the low snowfall intensity will keep this concern fairly minimal.  Unless you are going to be out exploring the mountains late tonight by headlamp, this should not be a concern at all.  

Wednesday night the story will begin changing dramatically as heavy snow fall rates begin and continue through Thursday night as a significant Atmospheric River brings heavy moisture to our area.  Avalanche danger will almost without a doubt rise to HIGH, and possibly beyond.  This intense loading, the highest we’ve seen yet this season, could very well re-activate the deeper weak sugary facet layers in the snowpack, and VERY large avalanches could become a real possibility.      

Weather and CURRENT CONDITIONS
weather summary

*Winter Storm Watch in effect Wednesday afternoon thru Thursday night*

Today will be mostly cloudy with a chance of snow showers in the afternoon and evening, with up to 2” of new snow above 8000’ by dark.  Around 10000’ expect highs in the mid to upper 30s and SW winds gusting into the 40s.  Relatively light snow should continue Tuesday night thru Wednesday, with the potential of up to a foot of total new snow at high elevations by Wednesday afternoon.

Wednesday night thru Thursday night is the main attraction, with high confidence of a major Atmospheric River bringing warm heavy tropical moisture centered over southern Mono County, 2-4’ of snow above 8500’, and up to 6’ in localized areas along the Sierra crest.  Snow line should remain above 8000’ for the majority of this storm until the tail-end when a cold front moves in and begins dropping snow line down to 6000’.  

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Chance of snow in the afternoon. Cloudy. Chance of snow and rain. Cloudy. Rain and snow likely.
Temperatures: 40 to 46 deg. F. 30 to 35 deg. F. 36 to 42 deg. F.
Wind Direction: South Southwest Southwest
Wind Speed: 10 to 15 mph. Gusts up to 25 mph. 15 to 20 mph with gusts to 40 mph shifting to the south 20 to 30 mph with gusts to 60 mph after midnight. 20 to 35 mph with gusts to 65 mph.
Expected snowfall: Up to 2 in. 2 to 5 in. 1 to 5 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Chance of snow in the afternoon. Cloudy. Snow likely. Cloudy. Snow likely in the morning, then snow in the afternoon.
Temperatures: 33 to 38 deg. F. 24 to 30 deg. F. 29 to 34 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 20 to 30 mph. Gusts up to 45 mph. 25 to 35 mph with gusts to 60 mph increasing to 35 to 50 mph with gusts to 80 mph after midnight. 30 to 45 mph with gusts to 70 mph increasing to 40 to 55 mph with gusts to 85 mph in the afternoon.
Expected snowfall: Up to 2 in. 2 to 5 in. 2 to 6 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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