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Avalanche Advisory for 2018-02-25 07:00

  • EXPIRED ON February 26, 2018 @ 7:00 am
    Published on February 25, 2018 @ 7:00 am
  • Issued by Andrew Kiefer - Mt Shasta Avalanche Center
  • February 25, 2018 @ 7:00 am

    Advisory Hotline: (530) 926-9613

  • The wind slab problem is developing near and above treeline on S-SE-E-NE-N aspects. Fresh wind slabs will continue to grow in size and distribution with the small incoming storm over the next 24 hours. Expect increasing avalanche danger tomorrow. For today, avalanche danger will remain LOW for all elevations.

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

Avalanche Problem 1: Wind Slab

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    Very Likely
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Wind slabs 6-12 inches thick can be found in isolated areas near and above treeline on S-SE-E-NE-N aspects. Many snow surfaces remain firm and icy, but in gullies, terrain depressions and on leeward slopes, evidence of wind slabs can be found. Small but sensitive cornice formations can also be found near and above treeline, and are an obvious sign of the recent wind loading that has occurred. To avoid the wind slab problem, steer clear of obviously wind-loaded slopes and terrain features 35 degrees and steeper primarily between 8,000-9,000 ft.

     

    Advisory Discussion

    With 2-4 inches of snow forecast over the next 24 hours and continued northwest winds, the wind slab problem is a growing concern. The most significant wind loading has occurred on leeward slopes and terrain features near treeline. Upper elevation slopes on Mount Shasta are scoured, firm and icy. Many avalanche path start zones are even stripped down to bare ground. Watch for changing conditions with the incoming storm as fresh winds slabs grow in size and distribution.

    Recent Observations

    The Old Ski Bowl station recorded one inch of new snow over the past 24 hours, and the max wind gust at Grey Butte was over 90 mph. The morning and early afternoon hours yesterday brought cold and windy conditions with low visibility on the south side of Mount Shasta. Between 7,000-9,000 ft, 3-4 inches of low-density snow rests atop a rock hard old snow surface. Above 9,000 ft, the recent snow has blown to lower elevations and most snow surfaces are firm and icy. Wind loading has occurred near and above treeline on S-SE-E-NE-N aspects: drifts up to 2 ft deep, small cornice formations and wind slabs 6-12 inches thick. Wind slabs were isolated and small. However, shooting cracks were observed on a wind loaded E facing slope near treeline. 

    Weather and Current Conditions

    Weather Summary

    Expect partly cloudy skies today with a chance for snow in the afternoon. Very strong northwest winds will continue with gusts up to 70 mph possible above treeline. Tonight brings another chance for snow with .19 inches of water expected by 10 am tomorrow morning. This should translate into 2-4 inches of snow for the majority of the advisory area with snow levels dropping to 2,000 ft. Skies will clear tomorrow afternoon and dry and sunny weather is expected by Tuesday. A potent winter storm looks to impact the area late in the week.

    24 Hour Weather Station Data @ 4:00 AM

    Weather Station Temp (°F) Wind (mi/hr) Snow (in) Comments
    Cur Min Max Avg Avg Max Gust Dir Depth New Water Equivalent Settlement
    Mt. Shasta City (3540 ft) 28 21 44 32 4 N
    Sand Flat (6750 ft) station down
    Ski Bowl (7600 ft) 25.5 14 28.5 20 42.5 1 0.05 2
    Gray Butte (8000 ft) 22 13 22 16.5 25 91 NW
    Castle Lake (5870 ft) 22.5 19.5 32.5 25 9.7 1 0.8
    Mount Eddy (6509 ft) 20 17.5 26 21 3 15 SE 25.3 1.8 1.5
    Ash Creek Bowl (7250 ft) station down
    Ash Creek Ridge (7895 ft) station down

    Two Day Mountain Weather Forecast

    Produced in partnership with the Medford NWS

    For 7000 ft to 9000 ft
      Sunday Sunday Night Monday
    Weather A chance of snow between 10am and 4pm, then snow showers likely after 4pm. Increasing clouds and blustery. Snow showers and breezy. Chance of precipitation 100%. Snow showers likely, mainly before 10am. Partly sunny,
    Temperature (°F) 28 15 21
    Wind Direction W/SW W N
    Wind Speed (mi/hr) 15-20 mi/hr 10-15 mi/hr 10-15 mi/hr
    Expected Snowfall (in) 1 2-4 .5
    For 9000 ft to 11000 ft
      Sunday Sunday Night Monday
    Weather A chance of snow between 10am and 4pm, then snow showers likely after 4pm. Increasing clouds. Wind chill values as low as -15 degrees. Snow showers and windy. Chance of precipitation 100%. Wind chill values as low as -24. Snow showers likely, mainly before 10am. Partly sunny and cold. Wind chill values as low as -30.
    Temperature (°F) 13 0 -1
    Wind Direction W/NW NW N/NE
    Wind Speed (mi/hr) 45-55 mi/hr 40-50 mi/hr 25-35 mi/hr
    Expected Snowfall (in) 1 2-4 .5

    Season Precipitation for Mount Shasta City

    Period Measured (in) Normal (in) Percent of Normal (%)
    From Oct 1, 2017 (the wet season) 10.27 28.42 36
    Month to Date (since Sep 1, 2018) 0.16 6.15 3
    Year to Date (since Jan 1, 2018) 4.44 13.21 34

    Disclaimer

    This advisory does not apply to Ski Areas or Highways and is for the Mount Shasta, Castle Lake and Mount Eddy backcountry. Use this information for guidance only. You may find different conditions in the backcountry and should travel accordingly. This advisory expires on midnight of the date it was posted unless otherwise noted.