Avalanche Advisory: Sunday - Dec 22, 2019

THIS AVALANCHE ADVISORY EXPIRED ON December 23, 2019 @ 6:45 am
Avalanche Advisory published on December 22, 2019 @ 6:45 am
Issued by Steve Mace - ESAC

The avalanche danger will remain MODERATE this morning at mid and upper elevations and LOW at lower elevations. Expect the avalanche danger to rise quickly this afternoon as a strong winter storm impacts the area. Fresh, sensitive wind slabs will be the primary concern on northerly and easterly aspects near and above treeline as the risk of storm slab avalanches also increases in more sheltered areas on all aspects.  Strong winds are expected today accompanied by 3-8” of new snow. If we see snow totals on the high end of this range, we expect the Avalanche Danger to rise into the realm of CONSIDERABLE by this evening.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Expect fresh sensitive wind slabs to build in size and distribution throughout the day today. Concerning wind slabs will be most prevalent on northerly and easterly aspects near and above tree line. 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, drifting, 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 surface instabilities are virtually non-existent this morning you can expect the risk of storm slab avalanches to increase as the snow starts to accumulate this afternoon.  Watch for signs of instability 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

Things may change drastically by this afternoon. Recent cold clear weather has been weakening the upper snowpack, and observations continue to identify loose faceted grains below the surface of the snowpack.  While this has led to deteriorating rain crusts and recycled powder skiing over the past few days, this poor structure will become more problematic if we see a significant load of new snow today.  Surface instabilities may be more sensitive than we usually expect here in the sierra. Don’t let the promise of fresh snow and the holiday weekend lure you into making risky decisions today.  Keep an eye on the weather and its impacts on your local area and be ready for the stability to decrease quickly as this storm intensifies this afternoon.

recent observations
Submit Snowpack Observations
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12/21- June Lake- Snow conditions 

12/21- Mammoth Area - Snow Conditions

12/20 - Mammoth Area - Variable surface conditions, faceted grains, and propagating test results in the Sherwins

12/20 - June Lake - Snow conditions

12/20 - Mammoth Area - Decomposing crusts, variable surface conditions

12/19 - McGee Creek - Variable and firm conditions

Weather and CURRENT CONDITIONS
weather summary

 A strong storm is expected to impact the area today bringing cool temperatures, afternoon snow showers, and strong southerly winds.  Be prepared for the snow to start around 10 am and continue through the evening and into tomorrow.  Strong winds this morning will decrease throughout the day and should be more in the realm of moderate by this evening. 

While this afternoon offers our best chance for significant accumulation, intermittent snow showers should continue Monday and Tuesday, with decreasing wind speeds and colder temperatures.

 

 

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 then becoming cloudy. Slight chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 85%. Mostly cloudy then becoming partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 65%. Cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 65%.
Temperatures: 36 to 42. deg. F. 13 to 19. deg. F. 23 to 29. deg. F.
Mid Slope Winds: South 25 to 35 mph with gusts to 80 mph. South 15 to 25 mph. Gusts up to 50 mph decreasing to 35 mph after midnight. East around 15 mph with gusts to 30 mph.
Expected snowfall: 70% probability of 3 to 7 inches. 30% probability of 7 to 10 inches. | SWE = 0.25-0.50 inch. in. 70% probability of 1 to 4 inches. 30% probability of 4 to 6 inches. | SWE = up to 0.20 inch. in. 70% probability of 1 to 2 inches. 30% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny then becoming cloudy. Slight chance of snow in the morning, then snow in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 95%. Mostly cloudy. Snow in the evening, then chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 80%. Cloudy. Snow likely. Snow levels below 7000 feet. Chance of precipitation is 70%.
Temperatures: 29 to 35. deg. F. 8 to 13. deg. F. 16 to 22. deg. F.
Ridge Top Winds: South 40 to 60 mph decreasing to 30 to 50 mph in the afternoon. Gusts up to 85 mph. Southwest 25 to 35 mph with gusts to 50 mph becoming south 15 to 25 mph with gusts to 35 mph after midnight. East 15 to 20 mph with gusts to 30 mph.
Expected snowfall: 70% probability of 3 to 8 inches. 30% probability of 8 to 12 inches. | SWE = 0.35-0.55 inch. in. 70% probability of 1 to 4 inches. 30% probability of 4 to 6 inches. | SWE = up to 0.30 inch. in. 70% probability of 1 to 2 inches. 30% probability of 2 to 4 inches. | SWE = up to 0.20 inch. 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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