Avalanche Advisory: Friday - Feb 9, 2018

THIS AVALANCHE ADVISORY EXPIRED ON February 10, 2018 @ 6:31 am
Avalanche Advisory published on February 9, 2018 @ 6:31 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Friday (2/9) - The overall avalanche danger remains LOW. Another round of clear skies, light winds, weak overnight freezes, combined with well above seasonable temperatures during the day will increase the potential for Loose Wet avalanches on E - S - W aspects. Limited snow coverage on solar aspects will limit the problem to areas where snow is present. Use caution in steep, rocky terrain as temperatures climb through the day and the snow becomes wet.

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

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: Loose Wet
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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
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    Very Large
    Large
    Small

Today (Friday) – Once again, overnight lows remained very warm with many locations struggling to fall below freezing for any length of time. Forecasted highs today will, once again, climb to 10 to 20 degrees above average. As a result, anticipate the snowpack to thaw quickly during the day on solar aspects (E-S-W) in the mid and upper elevations where snow is present, especially in steep, rocky terrain that has retained more snow. Use extra caution in and around rock outcrops, below cliff bands, or where the snowpack is exceptionally shallow where triggered releases are more likely. Timing is critical for avoiding Loose Wet releases. As temperatures begin to rise during the day, anticipate easterly aspects thawing first, followed by southerly, and then westerly as the sun moves across the sky. The lower elevations generally thaw more quickly than higher elevations. Watch for signs of unstable snow: large roller balls, deep ski penetration, and small point releases. Small point releases can be a sign that larger avalanches are increasingly possible. Loose Wet avalanches typically involve the snow near the surface of the snowpack but can trigger larger deeper releases. Time your travels to be out of steep sunny terrain before the snow thaws from the heat of the day.

Loose Wet slides are dense and heavy, which can make it difficult to extract yourself, if entrained, and are capable of carrying a rider into hazardous terrain or lead to possible burial when combined with a terrain trap that favors deep burial.

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

 

advisory discussion

Solar Aspects - High pressure remains parked off the coast of California and continues to deflect the storms to the north of the forecast region. This pattern is responsible for maintaining the warm air mass over west coast with daytime temperatures running 10 to 20 degrees above average while overnight lows struggle to fall below freezing in many locations. The result is an increased threat of wet instabilities on solar aspects (E-S-W), as long as the high-pressure ridge remains in place off the California coast. The limited snow coverage on southerly aspects will limit Loose Wet activity to isolated terrain that continues to retain sufficient snow (i.e. east to southeast facing gullies and cirques). Exposed rocky terrain features can introduce tremendous amounts of heat into the snowpack as they warm and can cause rapid localized thawing. Timing your travels to be out of steep sunny terrain before the snow thaws from the heat of the day is key to avoiding wet instabilities. Snow coverage continues to be thin with plenty of hazards lurking below the snow surface, such as rocks, logs and stumps.

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.

Northerly aspects - Patchy persistent weakness continues to lurk within the snowpack with weak faceted sugar layers down about ~30 to ~60cm (12” to 24”) from the surface. Distribution is primarily confined to NE-N-NW aspects above ~9500’. Recent test results continue to show the potential for failure but relatively non-reactive. The northerly aspects remain somewhat cool but are showing signs of warming with the surface snow in mid-elevations warming and developing a melt/freeze crust. The crust maturity depends on solar exposure, duration, steepness, and shading. The snow is still somewhat soft in sheltered areas near treeline but the aspect window has narrowed to N to NE aspects and shading is key. Near treeline, where the persistent weakness exists, there is the potential to encounter small isolated older Wind Slabs that were deposited over facets in steep terrain, which could fail if a sufficient trigger is applied.   

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

Fri thru Sunday – Friday, very mild day with valley highs in the upper 50s to upper 60s. The axis of the high-pressure ridge will retrograde over the Pacific this weekend, allowing a couple of cold fronts to move through the region Sunday night. Saturday, a dry cold-front will push through the region by late afternoon with temperatures highs in the 40s (around 15 degrees colder) and increasing clouds, no precipitation is expected. Surface high-pressure builds into the Great Basin Saturday, with an east to west gradient over the Sierra bringing some moderate east winds to the Sierra (especially over the Sierra Crest) with gusts over the Sierra Crest reaching up to 50-60 mph from the east by evening. Sunday, temperatures rebound ahead of the next front with winds increasing with gusts 25-35 mph possible.

 

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny Clear Sunny
Temperatures: 51 to 59 deg. F. 28 to 33 deg. F. 40 to 46 deg. F.
Wind Direction: Light winds. Light winds becoming west West veering to north
Wind Speed: Gusts up to 20 mph in the afternoon. 10 to 15 mph with gusts to 30 mph after midnight. 10 to 15 mph with gusts to 30 mph. Increasing 20 to 30 mph with gusts to 50 mph in the afternoon.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny Clear Sunny
Temperatures: 45 to 50 deg. F. 25 to 30 deg. F. 34 to 39 deg. F.
Wind Direction: West West Northwest
Wind Speed: 10 to 15 mph. Gusts up to 25 mph in the afternoon. 15 to 25 mph. Gusts up to 25 mph increasing to 45 mph after midnight. 25 to 35 mph with gusts to 65 mph.
Expected snowfall: 0 in. 0 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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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