Avalanche Advisory: Wednesday - Feb 13, 2019

THIS AVALANCHE ADVISORY EXPIRED ON February 14, 2019 @ 6:36 am
Avalanche Advisory published on February 13, 2019 @ 6:36 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

Avalanche danger will rise to HIGH today due to heavy dense snow falling with extreme SW winds, and rain falling on snow at lower elevations.  Large dangerous wind slabs will form at all elevations, and rain-on-snow at lower elevations will likely lead to large deadly wet-slab releases.  Travel in or under avalanche terrain will NOT be recommended.

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Below Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Wind Slab
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Extreme winds began transporting snow at all elevations into sensitive wind slabs throughout the day yesterday.  As 1.5ft+ of new heavy sierra cement snow falls today accompanied by more extreme SW winds, large dangerous wind slabs will become widespread anywhere that terrain leads to decreased wind speeds and snow deposition.  Avoid being on or under potentially wind-loaded terrain at all elevations.  Natural avalanches will be LIKELY and human triggered avalanches VERY LIKELY.  

Avalanche Problem 2: Wet Slab
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This warm tropical storm will lead to quickly rising snowlines this morning, with rain likely above 8000’, and possibly reaching over 9000’ this afternoon. Rain-on-snow can quickly destabilize large masses of snow.  Deadly large wide natural wet-slab releases will be VERY LIKELY at lower elevations as rain water penetrates the snowpack, even on slopes that aren’t that steep.  Avoid being on or under snowy slopes that are being rained on, including snow covered roof-tops!

Avalanche Problem 3: Storm Slab
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Unlike our large storm last week, this storm is coming in up-side-down.  Temperatures are rising, and more-dense snow will be falling on top of less-dense snow.  This is a recipe for unstable snow.  In the few areas that are sheltered from the wind, this heavier sierra cement snow will quickly form dense slabs.  Natural and human triggered avalanches will be LIKELY.  Avoid being on or under slopes >~30° where snow is depositing.  Be aware that even a small steep slope that ends in a depression or gully can lead to a deep burial.  

advisory discussion

Snowline is a difficult thing for weather forecasters to predict with great accuracy. Confidence is large that rain will fall at least up to 8000’.  If rain falls up to 9000’, or even up to 9500’, the amount of terrain that will become dangerous due to wet slab releases will increase dramatically. As rain saturates the upper snowpack, destabilization resulting in an avalanche can occur rapidly, especially if there is a buried melt-freeze crust that can act as a lubricated bed surface. Roof-tops are very much like a crust in this case, so in town give snow covered roofs a wide berth!  After the initial saturation of the snowpack occurs, what did not avalanche will become more stable, especially as temperatures cool again.    

Weather and CURRENT CONDITIONS
weather summary

A major warm winter storm will bring copious amounts of moisture and extreme winds to our area thru Thursday night.  1.5ft+ of sierra cement snow is expected at higher elevations today.  Snowline will quickly rise this morning with rain possibly reaching over 9000’ by this afternoon.  SW winds will be extreme at times with periodic lulls. Gusts could reach up to 100mph even at lower elevations, and up to 115mph over ridge-tops. Temperatures are likely to reach above freezing near 10,000’.   Another 1-1.5ft+ of snow is expected tonight.  Intense snowfall continues thru Thursday as snowlines rapidly drop in the morning.  Less-intense cold snow is expected for Friday thru the weekend. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow through the day. Rain in the afternoon. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 100%. Cloudy. Snow and rain. Snow levels 8500 feet. Chance of precipitation is 95%. Cloudy. Rain in the morning. Snow through the day. Snow levels 8500 feet decreasing to 7000 feet in the afternoon. Chance of precipitation is 100%.
Temperatures: 35 to 43. deg. F. 29 to 34. deg. F. 33 to 41. deg. F.
Mid Slope Winds: Southwest 30 to 45 mph with gusts to 100 mph. Southwest 30 to 45 mph with gusts to 90 mph. South 30 to 50 mph with gusts to 85 mph.
Expected snowfall: 60% probability of 8 to 16 inches. 40% probability of 4 to 8 inches. | SWE = 0.85-1.30 inches. in. 70% probability of 7 to 14 inches. 30% probability of 15 to 20 inches. | SWE = up to 1.15 inches. in. 70% probability of 8 to 16 inches. 30% probability of 16 to 22 inches. | SWE = 0.95-1.40 inches. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow. Snow levels 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 100%. Cloudy. Snow. Snow levels 8500 feet. Chance of precipitation is 100%. Cloudy. Snow. Snow levels 8500 feet decreasing to 7000 feet in the afternoon. Chance of precipitation is 100%.
Temperatures: 28 to 34. deg. F. 24 to 29. deg. F. 26 to 31. deg. F.
Ridge Top Winds: Southwest 75 to 95 mph with gusts to 145 mph. Southwest 80 to 110 mph with gusts to 155 mph. Southwest 55 to 75 mph with gusts to 145 mph.
Expected snowfall: 80% probability of 12 to 20 inches. 20% probability of 20 to 28 inches. | SWE = 1.20-1.70 inches. in. 80% probability of 10 to 18 inches. 20% probability of 18 to 24 inches. | SWE = up to 1.45 inches. in. 70% probability of 12 to 20 inches. 30% probability of 20 to 30 inches. | SWE = 1.25-1.75 inches. 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 Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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