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Avalanche Advisory for 2018-04-06 06:35

  • EXPIRED ON April 7, 2018 @ 6:35 am
    Published on April 6, 2018 @ 6:35 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest
  • April 6, 2018 @ 6:35 am

    Advisory Hotline: (530) 926-9613

  • Heavy rain-on-snow and strong winds will impact Mount Shasta today. Expect rising avalanche danger as one gains elevation above the rain/snow line. Above treeline, MODERATE danger is possible this afternoon, rising to CONSIDERABLE danger tonight. For all other areas that receive rain on snow, the avalanche danger is LOW. Minor loose wet instabilities are possible, but not expected to be a serious problem. 

     

     

  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Avalanche Problem 1: Wind Slab

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  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
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  • Size ?
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    Very Large
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Snow levels are expected to begin at 9,000 ft today and rise to 10,500 ft later today/tonight. New snow combined with strong S winds will contribute to the development of wind slabs on leeward slopes above treeline. Firm, icy snow surfaces may provide ideal bed surfaces for wind slab avalanches.

Avoid wind slabs by traveling in windward areas where snow surfaces have been eroded. Avoid slopes greater than 35 degrees where wind loading has occurred. Evaluate conditions as you travel in safe terrain by looking for signs of the wind slab problem:

  • Smooth rounded wind pillows
  • Hollow sounding snow
  • Harder snow atop softer snow
  • Shooting cracks

Advisory Discussion

This afternoon and tonight will be the brunt of the storm. Expect high winds, heavy rain and ample snow at higher elevations. Warming temperatures resulting in rising snow levels will provide full value, WET conditions on Mount Shasta over the next 24 hours. Rising avalanche danger in alpine areas is a concern, as are environmental hazards. Below and near treeline areas will receive mostly rain on snow. 

 

Recent Observations

The cloud deck gradually descended upon Mount Shasta yesterday and by evening, the mountain was shrouded with clouds. A few rain drops fell in town during the day. At 1600 hrs, a light, dense dusting of snow was observed near and below treeline and the snow level was about 6,500 feet. 

Relevant data from Gray Butte and Old Ski Bowl weather stations in the last 24 hours:

  • Average temperature = 30 °F; high temperature = 35 °F
  • Water equivalent = 0.56 in. / 3 in new snow
  • Snow settlement = .2 in.
  • Light to moderate W and SW winds averaging 9 mi/hr, gusts up to 25 mi/hr.

Recent observations from the Old Ski Bowl:

  • Height of snow (HS) = 150-200 cm (60-80 in).
  • Trace of new snow above 6,500 ft.
  • No recent signs of instability. No loose wet avalanches.
  • Snowpack stability good.
  • 3-5 cm (1-2 in) of moist fist hard snow atop pencil hard melt forms up to 8500 ft.
  • Firm icy conditions above 9000 ft, old wind textured snow surfaces.

Weather and Current Conditions

Weather Summary

A frontal system pushes over California and Oregon this morning. A surge of tropical moisture associated with an atmospheric river will move east-northeastward from the Pacific and will be directed into northern California. The heaviest rain will be just to the south of us, but moderate to, at times, heavy rainfall will occur in portions of Siskiyou County where orographics will enhance rainfall. Another impact from this storm will be strong southerly winds so hold on to your hats if near and above treeline on the mountain! We are looking at close to 1.5" of water by tomorrow afternoon. Temperatures will rise today/tonight and then cool off tomorrow. Snow level forecasts are 9,000 feet today, 10,500 feet tonight, and 6,300 feet tomorrow. Another storm with lower snow levels appears to be lining up for next week. April's outlook indicates above average precipitation and normal temperatures.

 

 

24 Hour Weather Station Data @ 3:00 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) 43 42 52 45 2 N
Sand Flat (6750 ft) station down
Ski Bowl (7600 ft) 29 28.5 35 31.5 75.3 2.9 0.56 0.2
Gray Butte (8000 ft) 28.5 27 34 29.5 9 25 W
Castle Lake (5870 ft) 31.5 31.5 45 37.5 18.9 2.8 2
Mount Eddy (6509 ft) 33 30.5 38 34.5 1 10 S 41.3 4.9 2
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
  Friday Friday Night Saturday
Weather Rain. Chance of precipitation 100% Breezy, rain. Chance of precipitation is 100%. Breezy, rain and snow in the morning, then showers in the afternoon. Chance of precipitation is 90%.
Temperature (°F) 44 38 40
Wind Direction S S SW
Wind Speed (mi/hr) 10-15 20-25 20-25
Expected Snowfall (in) 0 0 0-.5
For 9000 ft to 11000 ft
  Friday Friday Night Saturday
Weather Snow. Windy. Chance of precipitation is 100%. Snow. Chance of precipitation is 100%. Snow. Wind chill values as low as -5. Windy. Chance of precipitation is 90%.
Temperature (°F) 38 20 20
Wind Direction SW SW SW
Wind Speed (mi/hr) 30-40 40-50 40-50
Expected Snowfall (in) 4-8 6-10 10-12

Season Precipitation for Mount Shasta City

Period Measured (in) Normal (in) Percent of Normal (%)
From Oct 1, 2017 (the wet season) 16.06 36.04 45
Month to Date (since Aug 1, 2018) 0.11 0.58 19
Year to Date (since Jan 1, 2018) 10.23 20.83 49

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.