Avalanche Advisory: Wednesday - Jan 9, 2019

THIS AVALANCHE ADVISORY EXPIRED ON January 10, 2019 @ 6:58 am
Avalanche Advisory published on January 9, 2019 @ 6:58 am
Issued by Steve Mace - ESAC

 Avalanche danger will rise to considerable at mid and upper elivations throughout the forecast area today with fresh Wind slabs likely and persistent slabs possible. 5-9” of snow is expected with moderate to strong south winds in upper elevations. Be on the look out for sensitive wind slabs on leeward slopes near and above tree line on W-NW-N-NE-E aspects and remember that even relatively small slides will add stress to the underling snowpack and have the potential to trigger a much larger avalanche.  Extra caution should be taken today while traveling in the backcountry. 

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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The primary concern today will be fresh wind slab development on northerly aspects at mid and upper elevations. These sensitive wind slabs will grow in size and likelihood through the day as snow totals increase and winds continue out of the south. You can use visual clues to identify and avoid wind loaded slopes over 35 degrees. Recent cornice growth, blowing snow, snowdrifts, and uneven snow surfaces are all signs that wind slabs are in nearby terrain. Wind slabs will be most sensitive in areas of fresh distribution; however, the extreme winds experienced over the weekend distributed snow in complex ways.   It could be possible to find lingering sensitive wind slabs at all elevations even in sheltered areas you wouldn’t normally expect to find them.  

Avalanche Problem 2: Persistent Slab
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In addition to the extreme winds over the weekend we received 3-4’ of new snow. This new load is sitting on a pretty poorly structured snowpack of weak facets in many areas.  New wind loading today will only add stress to these buried weak layers.  If you see obvious signs of avalanche danger, like recent avalanches, collapsing, or shooting cracks, avoid all slopes 35 degrees and steeper. Persistent slab avalanches are dangerous and difficult to predict, propagating long distances across slopes and running further down slope.  In addition to triggering these weak layers directly it will be possible for a smaller wind slab to step down and create a much larger avalanche.

Avalanche Problem 3: Storm Slab
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With up to 10" of snow possible today it is possible that we will see storm slab development this afternoon on all aspects at low and mid elevations.  As snow totals add up today be on the lookout in sheltered areas near and below tree line. 

advisory discussion

Recent weather events have set us up with a pretty complex situation.  Travel remains difficult in many areas with a very upside down snowpack.  Wind slabs have been observed in even the most sheltered areas and the overall structure remains poor.  

Significant settlement was observed yesterday.  This is a sign that the new storm snow is continuing to consulidate into a slab.  The presence of weak faceted snow underlying this developing slab is concerning. While these weak layers are deeper in the snow pack and harder to trigger, resulting avalanches are likely to be larger and more consequential. It’s likely that this persistent instability will remain for some time to come, challenging our patience and decision making ability.  Conduct carful snowpack evaluation.  When in doubt, be conservative in your route choice and avoid suspect terrain over 35°.

Weather and CURRENT CONDITIONS
weather summary

5-9” of snow is expected today accompanied by strong winds out of the south.   35-55 mph winds with gusts expected to reach 85mph this morning at upper elevations. Temperatures are expected to be warm today with a high of 32°F around 10,000’. Winds are expected to drop this evening to a moderate 25-35 mph as the storm begins to clear.

For tomorrow expect partly cloudy skies and continued warm temperatures.  Winds are expected to drop tomorrow (10-15 mph) and continue out of the south.  

There remains a chance of storms developing this weekend though precipitation rates look to be small at this point.

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 likely in the morning, then snow showers likely in the afternoon. 2-6" of snow expected. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 90%. Mostly cloudy. Slight chance of snow showers through the night. Partly cloudy.
Temperatures: 28 to 35. deg. F. 18 to 23. deg. F. 32 to 42. deg. F.
Mid Slope Winds: South 15 to 30 mph with gusts to 70 mph. Southwest 10 to 15 mph. Gusts up to 45 mph decreasing to 30 mph after midnight. Light winds.
Expected snowfall: 2-6" in. up to 1" in. none in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Cloudy. Snow likely in the morning, then snow showers likely in the afternoon. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 100%. Mostly cloudy. Chance of snow showers through the night. Snow levels below 7000 feet. Chance of precipitation is 30%. Partly cloudy.
Temperatures: 24 to 32. deg. F. 13 to 18. deg. F. 28 to 33. deg. F.
Ridge Top Winds: South 35 to 55 mph with gusts to 85 mph decreasing to 25 to 35 mph with gusts to 60 mph in the afternoon. Southwest 20 to 35 mph with gusts to 50 mph decreasing to 15 to 25 mph with gusts to 40 mph after midnight. South 10 to 15 mph. Gusts up to 25 mph in the morning.
Expected snowfall: 4-9" in. up to 1" in. none 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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