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Avalanche Advisory for 2018-02-26 06:38

  • EXPIRED ON February 27, 2018 @ 6:38 am
    Published on February 26, 2018 @ 6:38 am
  • Issued by Andrew Kiefer - Mt Shasta Avalanche Center
  • February 26, 2018 @ 6:38 am

    Advisory Hotline: (530) 926-9613

  • Fresh wind slabs 1-2 feet thick may exist on SW-S-SE-E-NE aspects near and above treeline. Human triggered wind slab avalanches are possible while natural avalanches are unlikely. The avalanche danger is MODERATE near and above treeline and LOW below treeline.

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

Avalanche Problem 1: Wind Slab

  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

New snow and northerly winds have created fresh winds slabs near and above treeline on SW-S-SE-E-NE aspects. Wind slabs could be human triggered on leeward slopes and terrain features 35 degrees and steeper. Watch for blowing snow, cornices, textured snow surfaces and drifts of snow as evidence that wind loading has occurred. With just a few inches of low-density snow falling on slick and icy old snow surfaces, the new snow may have been stripped off many slopes above treeline and transported to lower elevations. Be especially careful of obviously wind-loaded slopes between 7,500-9,000 ft. 


    Advisory Discussion

    Snow totals from the past 24 hours range from 1-4 inches throughout the advisory area. Northwest winds have created shallow wind slabs and loaded leeward slopes, gullies and terrain depressions near and above treeline. Most likely, the new snow has been stripped away from many slopes above 9,000 ft on Mount Shasta leaving widespread firm and icy snow surfaces. Shallow snowpack hazards still exist and the new snow has just barely covered many obstacles and patches of bare ground.

    Recent Observations

    The Old Ski Bowl weather station recorded .13 inches of SWE (snow water equivalent) and 4 inches of new snow. Precipitation began at 10 pm last night. Winds at Grey Butte shifted from the NW to SW to W overnight with a max wind gust of 65 mph. No signs of unstable snow or avalanches were observed during a tour to Sun Bowl yesterday. The snow from the last storm has settled 2-3 inches below treeline, and has been almost completely stripped away from most slopes near and above treeline. Unreactive and isolated winds slabs up to 8 inches thick were found on SE aspects near treeline. A small cornice still exists at the top of Sun Bowl. Many avalanche path start zones including Sun Bowl and Powder Bowl are scoured down to bare ground. Ridgelines and exposed terrain features are as well. The snowpack is 1-3 ft deep below treeline with many bare patches.

    Weather and Current Conditions

    Weather Summary

    Light snow showers will continue through 10 am this morning with an additional .5 inches of snow possible. Westerly winds will shift to the north/northeast blowing 20-30 mph above treeline. Clouds will gradually break down throughout the day. Tonight will be clear and cold. Sunny skies are expected tomorrow. A potent winter storm under southwest flow will impact northern California Wednesday through Friday bringing heavy snowfall.

    24 Hour Weather Station Data @ 6:00 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) 32 27 47 35.5 1 N
    Sand Flat (6750 ft) station down
    Ski Bowl (7600 ft) 16.5 16.5 30.5 22.5 43 3 0.15 3
    Gray Butte (8000 ft) 16.5 16.5 25.5 20.5 20 64 W
    Castle Lake (5870 ft) 23 22.5 44 28.5 9.5 2 2
    Mount Eddy (6509 ft) 20.5 20 34 26 2 14 SSE 27 3 1
    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
      Monday Monday Night Tuesday
    Weather A 40% chance of snow showers, mainly before 10am. Partly sunny, Mostly clear. Wind chill values as low as -11. Mostly sunny. Wind chill values as low as -10.
    Temperature (°F) 17 15 27
    Wind Direction NW N N
    Wind Speed (mi/hr) 5-10 mi/hr 10-15 mi/hr 10-15 mi/hr
    Expected Snowfall (in) .5 0 0
    For 9000 ft to 11000 ft
      Monday Monday Night Tuesday
    Weather A 40% chance of snow showers, mainly before 10am. Partly sunny and cold. Wind chill values as low as -29. Mostly clear and cold. Wind chill values as low as -34. Mostly sunny. Windy. Wind chill values as low as -31.
    Temperature (°F) 1 -1 15
    Wind Direction N/NE N/NE N
    Wind Speed (mi/hr) 20-30 mi/hr 25-35 mi/hr 40-50 mi/hr
    Expected Snowfall (in) .5 0 0

    Season Precipitation for Mount Shasta City

    Period Measured (in) Normal (in) Percent of Normal (%)
    From Oct 1, 2017 (the wet season) 10.28 28.69 36
    Month to Date (since Sep 1, 2018) 0.17 6.42 3
    Year to Date (since Jan 1, 2018) 4.45 13.48 33


    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.