Avalanche Advisory: Sunday - Feb 23, 2020

THIS AVALANCHE ADVISORY EXPIRED ON February 24, 2020 @ 7:00 am
Avalanche Advisory published on February 23, 2020 @ 7:00 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

7” of new snowfall was recorded in the southern reaches of the forecast zone yesterday, with wind speeds ideal for transporting snow that will continue thru today.  Avalanche danger will vary widely across the region today.  Sensitive wind slabs will continue to form, and sunny and warm conditions could knock them loose above you.  Areas of CONSIDERABLE avalanche danger exists at treeline and above for the southern zone which received the most new snow, transitioning to LOW danger for the northern zone which received only trace amounts of new snow.  Evaluate new snowfall carefully, and avoid being on or under slopes with significant fresh wind-load. 

 

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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New snowfall varied greatly yesterday across the forecast zone, with much greater amounts of 7” to the south and trace amounts to the north. NE winds increased yesterday afternoon, and will shift out of the W and NW today continuing in the 20-30mph ideal snow transport range. Where new snow has fallen, fresh sensitive wind slabs will likely be found just below ridgelines, sidewalls of gullies and cross-loaded slopes.  Slick underlying conditions could make these slabs less likely to bond, and result in them running farther than expected.  Human triggered avalanches are likely, and natural avalanches are possible due to continued wind loading and warming from sun exposure.  Carefully evaluate local new snowfall amounts, watch for signs such as blowing snow and new cornice formation, and avoid being on or under areas with significant fresh wind-load.  Be especially cautious of gully or couloir features that funnel falling snow or rocks from broad expanses.                  

 
Avalanche Problem 2: Loose Wet
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For areas that received fresh snow, sunny skies and warm temperatures are likely to trigger loose wet avalanches on E-SE-S-SW-W aspects today as they warm.  Watch for signs of small rollerballs originating from rock bands as early indications that larger loose-wet avalanches could be possible.  A loose-wet avalanche could also trigger a more consequential fresh wind slab.         

 
Avalanche Problem 3: Storm Slab
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For the southern areas that received the most new snowfall, human triggering of storm slabs in sheltered areas could be possible in steep terrain, as well as loose sloughs.  Be especially cautious of suspect slopes above terrain traps such as gully bottoms.  

 
advisory discussion

 

Snow fall varied widely across the forecast zone.  The snow sensor at Sawmill in the Bishop region at 11,900’ recorded 7” of new snowfall, Rock Creek at 9600’ recorded 4”, field observations in the Mammoth Lakes Basin around 10,000’ measured ~1.5”, while snow sensors Mammoth and north recorded barely an inch.

 

Variable and slick underlying conditions abound.  A fall will be hard to self arrest in many areas, and even a small avalanche could have a very bad outcome especially with all the obstacles that exist. 

Weather and CURRENT CONDITIONS
weather summary

After yesterday’s unsettled weather and snowfall, today will be sunny and warm with west to northwest winds in the 20-30mph range.  Temperatures are expected to reach near 40°F up to 10,000’, and even over 11,000’ for the southern reaches of the forecast zone.

 

High pressure and sunny skies will persist into next week, with unseasonably warm temperatures reaching 10-15°F above average by mid-week. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Clear. Snow levels 7500 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 39 to 49. deg. F. 21 to 27. deg. F. 39 to 49. deg. F.
Mid Slope Winds: Northwest around 15 mph with gusts to 35 mph. Northwest around 15 mph with gusts to 35 mph in the evening becoming light. Light winds becoming northwest around 15 mph in the afternoon. Gusts up to 30 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = none. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny. Snow levels below 7000 feet increasing to 7000 feet in the afternoon. Chance of precipitation is 0%. Clear. Snow levels 7000 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 0%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 0%.
Temperatures: 29 to 37. deg. F. 16 to 21. deg. F. 30 to 38. deg. F.
Ridge Top Winds: West 15 to 25 mph. Northwest 15 to 25 mph. Northwest 15 to 25 mph.
Expected snowfall: No accumulation. | SWE = none. in. No accumulation. | SWE = none. in. No accumulation. | SWE = 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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