Avalanche Advisory: Sunday - Feb 11, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON February 12, 2018 @ 6:34 am
Avalanche Advisory published on February 11, 2018 @ 6:34 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Sunday (2/11) - The avalanche danger remains LOW overall today but will begin rising toward moderate this evening with precipitation onset. Forecasted moderate to strong Southwesterly winds ahead of an approaching cold front could form small isolated Wind Slabs, near and above treeline on NW-NE-SE aspects where upwind fetches have transportable snow.

Below ~9,000’, natural and triggered releases are unlikely due to thin snow coverage (below threshold).​

Caution – Possible Slide for Life conditions in the AM or as slopes begin to refreeze on solar aspects. A minor slide into hazardous terrain can have serious consequences. Crampons and Ice Axe recommended in exposed terrain.

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.

No Rating

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Below Treeline
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1: Wind Slab
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    Certain
    Very Likely
    Likely
    Possible
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    Very Large
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Today’s forecast is calling for moderate Southwesterly winds becoming strong toward the afternoon. Though southwesterly fetches are mostly free of snow, in favored locations it may be possible to transport enough snow to form Wind Slabs on NW-NE-SE aspects. If encountered, initially these will be isolated and small, primarily found near and above treeline. With the onset of precipitation late this afternoon to evening, Wind Slabs will begin to build and form more widely with the hazard climbing toward Moderate by Monday AM.  

Caution – On southerly aspects, possible Slide for Life conditions in the AM or as slopes begin to refreeze. A minor slide into hazardous terrain can have serious consequences. Crampons and Ice Axe recommended in exposed terrain.

advisory discussion

Today (Sunday) – The weather forecast calls for sunny skies early, then becoming partly cloudy with high temperatures ranging from mid 20’s to low 40’s. The hard freeze last night, cool temperatures today, increasing clouds, and forecasted breezy conditions will keep the snow well frozen in most locations through the day, which will limit the concern for the wet instabilities that have been the primary concern for the past couple of weeks.

The approaching storm is another “inside slider”, which generally usher in colder air and brief light to moderate snowfalls, which will bring welcomed relief from an otherwise dry start to February. Snowfall amounts of 2”to 6” are expected over the higher elevations by Tuesday AM with moderate to strong Southwesterly winds, becoming Northeasterly late Monday. The cold dry snow will be slow to bond to the icy spring-like snow surface, increasing the potential for tender slab formation. This combination of winds, low-density snow, and icy snow surface will readily form Wind Slabs, initially on NW-NE-SE aspects near and above treeline. Late Monday, as the cold front begins to move off to the east, winds are forecasted to swing to the Northeast. These moderate winds will form a new round of Wind Slabs on NW-SW-SE aspects near and above treeline.  Despite the elevated avalanche risk, this is a welcomed break in the pattern that has dominated the weather since late January (1/27). Snow coverage continues to be thin with plenty of hazards lurking below the snow surface, such as rocks, logs and stumps. The new snow will only hide the hazard while providing little protection.

Patchy persistent weaknesses continue to dwell within the snowpack with weak faceted sugar layers down about ~30 to ~60cm (12” to 24”) from the surface in most locations. Distribution is primarily confined to NE-N-NW aspects above ~9500’. Recent test results continue to show the potential for failure but currently relatively non-reactive. The approaching cold front is forecasted to produce 2” to 6” of low-density snow. This is unlikely enough load to stress the underlying persistent weakness enough for it to become widely reactive. However, near treeline where the persistent weakness exists, there is the potential that a Wind Slab failure could trigger a larger avalanche on these deeper weaknesses.

Below ~9,000’, natural and triggered releases are unlikely due to thin and well-anchored snow coverage (below threshold).​

 

Weather and CURRENT CONDITIONS
weather summary

Sun thru Monday – Southwesterly winds will increase today in advance of an approaching cold front with winds of 35-40 mph today over the higher elevations. The cold front moving in tonight is moisture starved, although there should be just enough moisture and dynamics to get a quick burst of snow along the cold front with the best chance of precipitation from 6 PM until midnight Monday when atmospheric lift over the colder post-frontal airmass is strongest with 1” to 2” possible. The cold front will push through the region Monday morning, with a cool and brisk day for all areas along with lingering light snow showers. Temperatures will be around 10 degrees below normal. Another shortwave trough moves down along the West Coast Monday Night with an upper level low moving over northern NV/CA while a secondary wave swings around the Bay Area Monday Night, helping to increase the easterly surface winds over our area. This will set up a deformation zone in Mono County starting Monday afternoon through Tuesday morning with favorable upslope flow and precipitation over the Eastern Sierra, which could see another several inches.

 

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 partly cloudy. Mostly cloudy then becoming partly cloudy. Chance of snow. Partly cloudy then becoming cloudy. Scattered snow showers in the morning, then widespread snow showers in the afternoon.
Temperatures: 35 to 43 deg. F. 14 to 19 deg. F. 21 to 27 deg. F.
Mid Slope Winds: Southwest Southwest West
Expected snowfall: 0 in. Up to 1 in. Up to 2 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Sunny then becoming partly cloudy. Mostly cloudy then becoming partly cloudy. Snow likely. Partly cloudy then becoming cloudy. Scattered snow showers in the morning, then widespread snow showers in the afternoon.
Temperatures: 28 to 34 deg. F. 8 to 13 deg. F. 12 to 17 deg. F.
Ridge Top Winds: West Southwest becoming west West
Expected snowfall: 0 in. Up to 1 in. Up to 2 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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