Avalanche Advisory: Wednesday - Mar 18, 2020

THIS AVALANCHE ADVISORY EXPIRED ON March 19, 2020 @ 6:55 am
Avalanche Advisory published on March 18, 2020 @ 6:55 am
Issued by Steve Mace - ESAC

The Avalanche danger will be CONSIDERABLE upper elevations today, and MODERATE at middle and lower elevations. Fresh and sensitive wind slabs will be the primary concern today on northerly and easterly aspects at mid and upper elevations. Loose-dry sloughing will be less concerning, however still possible to find in more sheltered areas. It will also be important to keep in mind that significant weight has been to a weak underlying snowpack over the last few days.  Persistent slab avalanches may be possible on northerly and easterly aspects at all elevations.  Cautious route-finding and conservative decision making will be essential if you travel into the backcountry today.  

Avalanche Danger will be more concerning around Mammoth and in areas to the north which received notably more snow than the southern reaches of the forecast area. 

3. Considerable

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

2. Moderate

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

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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Storm totals ranging from 1-4’ have been observed throughout the range and field observations have identified this new snow to be very low density. Moderate to strong winds picked up late yesterday and continued through the evening. We can expect significant redistribution of loose surface snow occurred overnight.  Wind speeds are predicted to drop this morning but remain in the range of prime loading speeds. While the size and sensitivity may vary today, wind slabs sensitive to human triggers are likely on NW-N-E-SE aspects at mid and upper elevations. Expect continued slab development to occur on leeward slopes throughout the day today as moderate southwesterly winds continue to impact the area.  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, large drifts, dense hollow feeling snow, recent cornice growth, and uneven snow surfaces can help you identify and avoid areas of recent wind deposits.

Avalanche Problem 2: Loose Dry
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Field observations continue to indicate ample amounts of low-density powder residing on the surface. Loose-dry avalanches remain possible in sheltered steep terrain today.  Be particularly cautious on steep slopes over 35° and in areas where terrain features increase the consequence of an avalanche. Steep confined gullies, cliff bands, creek beds, and mid-slope benches all pose an increased hazard.  While we typically think of sloughing as a relatively easy problem to manage, storm totals in some areas are over 3ft deep and a resulting Loose-dry avalanche in the wrong place today could certainly be large enough to bury a skier. 

Avalanche Problem 3: Persistent Slab
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Significant weight has been added to the snowpack this week with 1-4’ of new snow and SWE measurements around 3” in the mammoth area. In addition, significant collapsing and several large natural slab avalanches were observed in the northern part of the range yesterday. Prior to this storm, the old snow surface was variable across the range, composed in many areas of a verity of crust facet combos or week sugary snow. While avalanches resulting on these deeper weak layers may be harder to trigger than the problems mentioned above, the consequences are likely to be large. It will be important to give the snowpack time to adjust to this new load and realize that even a small wind slab or loose dry avalanche may step down and result in a more sizable slab avalanche.  

Forecaster confidence remains low as to the distribution and sensitivity of this problem. However, we expect northerly and easterly terrain at all elevations to be the most likely place to find this poor structure.  Solar aspects and many areas at lower elevations were bare ground before this most recent storm and are far less likely to be problematic.

Remember that persistent slab avalanches often propagate across and beyond terrain features that would otherwise confine surface instabilities such as wind or storm slab and in some cases, persistent avalanches can be remotely triggered from adjacent slopes. Give yourself a wide safety margin, be wary of hazard that may reside above you, and use terrain choice to limit your exposure.

advisory discussion

A fresh blanket of low-density powder has brought a welcome change to the range after a very long dry spell. This recent increase in ski quality combined with other world events has led to a large uptick in backcountry use. Don’t let the fresh snow, mild weather, and pressures from the increased crowds lure you into making poor decisions today. Human triggered avalanches remain likely and we are dealing with multiple avalanche problems that have a variety of implications on travel. It is also worth remembering that despite the recent storm overall the coverage remains thin. Keep an eye out for shallowly buried rocks and trees and move cautiously through the landscape.

 

Weather and CURRENT CONDITIONS
weather summary

Expect cloudy skies and scattered snow showers today.  While snow totals are not expected to be high we may see periods of heavy snow today and accumulations of an inch or two.  Temperatures will remain cold with highs below freezing at lower elevations and in the low 20°F at upper elevations. Moderate winds will continue out of the southwest today with ridgetops gusts up to 35 mph. 

We can expect unsettled weather to continue through the week as our current round of low pressure exits the area to the east and another system approaches from the west. While we can expect intermittent snow showers and continued cold temperatures this week, a more impressive storm may impact the area late this weekend or early next week.

 

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: Partly cloudy then becoming mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 40%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 55%. Partly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%.
Temperatures: 24 to 32. deg. F. 10 to 16. deg. F. 25 to 33. deg. F.
Mid Slope Winds: Southwest around 15 mph in the morning becoming light. Gusts up to 35 mph. Light winds. Gusts up to 30 mph in the evening. Light winds.
Expected snowfall: up to 2 inches. | SWE = less than 0.10 inch. in. 60% probability of 1 to 3 inches. 40% probability of 3 to 6 inches. | SWE = up to 0.15 inch. in. 60% probability up to 2 inches. 40% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 50%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 55%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 50%.
Temperatures: 16 to 22. deg. F. 4 to 9. deg. F. 17 to 23. deg. F.
Ridge Top Winds: Southwest 15 to 25 mph with gusts to 35 mph. West 15 to 20 mph. Gusts up to 30 mph in the evening. Light winds.
Expected snowfall: 0% probability up to 2 inches. | SWE = less than 0.10 inch. in. 60% probability of 1 to 3 inches. 40% probability of 3 to 6 inches. | SWE = up to 0.15 inch. in. 60% probability of 1 to 2 inches. 40% probability of 2 to 5 inches. | SWE = up to 0.15 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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