Avalanche Advisory: Saturday - Dec 14, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 15, 2019 @ 6:59 am
Avalanche Advisory published on December 14, 2019 @ 6:59 am
Issued by Steve Mace - ESAC

The Avalanche danger will be CONSIDERABLE at mid and upper elevations today, and MODERATE at lower elevations. Fresh, sensitive wind slabs will be the primary concern today on northerly and easterly aspects at mid and upper elevations. Storm slabs will be less concerning, however still possible to find in more sheltered areas at lower elevations. Cautious route-finding and conservative decision making will be essential as you travel into the backcountry today.  

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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5” of new snow was recorded at the base of Mammoth Mountain this morning.  This fresh snow was accompanied by very strong southwest winds. Expect continued slab development to occur on leeward slopes throughout the day today as strong winds continue to impact the area.  Wind slabs will range in size and sensitivity today from fresh and sensitive to older and more stubborn.  Expect problematic wind slabs to be most prevalent on northerly and easterly aspects at mid and upper elevations. However, it is also important to remember that strong winds can distribute snow in unexpected ways. Don’t be surprised to find wind deposits at lower elevations and further down slopes than you may typically expect to find them.  Do your own localized assessments and be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions.   Surface clues such as blowing snow, recent cornice growth, and uneven snow surfaces can help you identify and avoid areas of recent wind deposit.

Avalanche Problem 2: Storm Slab
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While relatively small amounts of new snow fell overnight at lower elevations it is likely that more snow accumulated at higher elevations.  It may be possible to find storm slab development in more sheltered areas protected from the wind.  Be on the lookout for signs of surface instabilities such as shooting cracks, wumphing, and recent avalanche activity, and be aware that loose unconsolidated sloughs can entrain quite a bit of snow and potentially carry a skier through some unpleasant terrain.  Heightened awareness is recommended in sheltered areas over 35°.

 

advisory discussion

Strong Sierra winds remain the driving force of change here on the east side. However, the warm spell and rain showers experienced on the front end of this most recent storm are adding complexity to the snowpack today.  Typically the transition from warm to cold during a precipitation event is a beneficial thing leading to a right-side-up situation.  While this is still a likely outcome, a hard rain crust was reported by Mammoth Mountain ski patrol on Friday and observed in elevations approaching 10,000’.  Don’t be afraid to dig in and investigate this interface as the presence of a buried rain crust may exasperate surface instabilities today. 

Weather and CURRENT CONDITIONS
weather summary

 Expect scattered snow showers throughout the day today accompanied by cold temperatures and continued strong winds out of the southwest. mid-slope winds are expected to reach as high as 40 mph with gusts as high as 85mph on ridgetops this morning.  A second wave of moisture is expected to move through the area this evening as temperatures drop into the single digits.  Winds will shift to the west and begin to slow this afternoon and into this evening.

 

For Sunday, we can expect partly cloudy skies are becoming clear by the afternoon as the low-pressure trough exits the region. Temperatures are likely to stay cold as the winds decrease to more moderate speeds and shift to the Northwest.  

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: Mostly cloudy then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 50%. Partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 28 to 34. deg. F. 10 to 15. deg. F. 19 to 27. deg. F.
Mid Slope Winds: Southwest 20 to 40 mph with gusts to 65 mph. West 15 to 25 mph. Gusts up to 50 mph decreasing to 40 mph after midnight. Northwest around 15 mph with gusts to 35 mph.
Expected snowfall: 80% probability of up to 2 inches. 20% probability of 2 to 4 inches. | SWE = less than 0.20 inch. in. up to 2 inches. | SWE = less than 0.10 inch. in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Mostly cloudy then becoming partly cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 65%. Partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 45%. Partly cloudy then becoming sunny. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 21 to 27. deg. F. 4 to 9. deg. F. 12 to 18. deg. F.
Ridge Top Winds: Southwest 40 to 70 mph with gusts to 85 mph decreasing to 30 to 45 mph with gusts to 65 mph in the afternoon. West 15 to 30 mph with gusts to 45 mph. Northwest 15 to 30 mph with gusts to 45 mph.
Expected snowfall: 80% probability of up to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.20 inch. in. up to 2 inches. | SWE = less than 0.10 inch. in. 0 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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