Avalanche Advisory: Saturday - Jan 25, 2020

THIS AVALANCHE ADVISORY EXPIRED ON January 26, 2020 @ 6:48 am
Avalanche Advisory published on January 25, 2020 @ 6:48 am
Issued by Steve Mace - ESAC

Low avalanche danger exists at all elevations today. Isolated areas may exist on northerly and easterly aspects where a skier’s weight could trigger a persistent slab avalanche. Practice safe travel techniques and evaluate terrain carefully.

1. Low

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Above Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Persistent Slab
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  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

We typically think of a persistent slab avalanche problem as one that is quick to rise after a large storm and persists days or even weeks after the skies clear. In our case, we have been seeing more significant signs of reactivity in the buried weak layers as time has passed. Numerous large collapses, surface cracking and propagating test results have been observed throughout the range.  While no avalanches breaking in these deeper weak layers have been reported, these signs of instability all indicate the potential is there. We expect the distribution of this problem to be isolated to steep slopes with poor structure and a contiguous slab. It is important to 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 and use terrain choice to limit your exposure.

 

advisory discussion

Over the last week since the storm on January 16th many field observations have come in highlighting our thin snowpack and poor structure. While our concern spiked initially over how the weak snowpack would accept the new load, natural and artificially triggered avalanches were confined to surface instabilities during and immediately following the storm. In the time since we have seen the new snow bonding well to the old snow surface, however, as this snow has settled, it has also formed a more cohesive slab. Numerous large collapses, surface cracking, and test results showing propagation potential have been reported from all corners of the range. It is worth noting that while a weak faceted snowpack has been found throughout the range at all elevations, we cannot point to a specific layer of concern. Instead, we are dealing with a variety of facet crust combos and large variability when it comes to slab density and thickness.  While the chances are good that the conditions exist somewhere in our range for a persistent slab avalanche to occur, it is likely that they are limited to isolated areas. Observations have indicated sparse coverage, particularly at lower elevations and on windward and solar aspects. For the most part, contiguous snowfields are limited to high-elevation cirques, while at mid and lower elevations, snowfields are broken by shallow reefs, exposed rock bands, and reappearing vegetation.  This variability may be working in our favor by bisecting weak layers and limiting the size of potential slabs. A large load of new snow would likely kick off a significant avalanche cycle, but for the time being, initiating an avalanche on these buried weak layers will require and artificial trigger.  Don’t be afraid to dig in and evaluate the underlying snowpack for instabilities and realize that given the spatial variability, conditions found in one area are not going to be representative of the big picture. 

 

Weather and CURRENT CONDITIONS
weather summary

Temperatures will be warm today with partly cloudy skies. Highs above freezing expected at upper elevations and daytime temperatures approaching 50° f at lower elevations. Winds are also expected to drop significantly today with ridgetop winds expected in the 20-30 mph range.

A brief period of unsettled weather is expected to move through the area tonight and into tomorrow. 1-2” is expected to arrive after midnight tonight and an additional 1-4” during daylight hours on Sunday. This snow will likely be accompanied by increasing winds and slightly cooler temperatures.

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: Partly cloudy. Mostly cloudy. Chance of snow after midnight. Snow levels 8500 feet decreasing to 7500 feet after midnight. Chance of precipitation is 40%. Mostly cloudy then becoming partly cloudy. Snow likely in the morning, then a chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 85%.
Temperatures: 39 to 47. deg. F. 27 to 33. deg. F. 31 to 39. deg. F.
Mid Slope Winds: Southwest around 10 mph. Southwest 10 to 20 mph. Gusts to 40 mph after midnight. Southwest 15 to 20 mph. Gusts up to 50 mph decreasing to 35 mph in the afternoon.
Expected snowfall: 0 in. 80% probability up to 1 inch. 20% probability of 1 to 3 inches. | SWE = less than 0.15 inch. in. 70% probability of 1 to 4 inches. 30% probability up to 1 inch. | SWE = up to 0.15 inch. in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Partly cloudy. Snow levels 7000 feet increasing to 8500 feet in the afternoon. Chance of precipitation is 0%. Mostly cloudy. Chance of snow after midnight. Snow levels 8500 feet decreasing to 7500 feet after midnight. Chance of precipitation is 50%. Cloudy then becoming partly cloudy. Snow in the morning, then chance of snow in the afternoon. Snow levels 7000 feet. Chance of precipitation is 95%.
Temperatures: 31 to 39. deg. F. 23 to 29. deg. F. 24 to 30. deg. F.
Ridge Top Winds: West to northwest 10 to 20 mph. Southwest 15 to 20 mph with gusts to 30 mph increasing to 30 to 40 mph with gusts to 60 mph after midnight. Southwest 30 to 45 mph with gusts to 60 mph decreasing to 20 to 30 mph with gusts to 45 mph in the afternoon.
Expected snowfall: 0 in. 80% probability up to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.25 inch. in. 70% probability 2 to 4 inches. 30% probability up to 2 inches. | SWE = up to 0.25 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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