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Avalanche Advisory for 2018-04-12 05:47

  • EXPIRED ON April 13, 2018 @ 5:47 am
    Published on April 12, 2018 @ 5:47 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest

Evaluate snow and terrain carefully today. Since yesterday afternoon, Mount Shasta has received nine inches of new snow accompanied by strong SW to NW winds. New snow sits on top of old, smooth, icy surfaces. Fresh wind slabs and loose dry avalanches are possible today. As visibility is gained above treeline, travel through avalanche terrain with caution.

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

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

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

Avalanche Problem 1: Wind Slab

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Upper elevations have likely received a foot or more of new snow. This coupled with strong SW to NW winds will contribute to the development of wind slabs that could be over 2 feet thick. Watch for blowing snow or evidence of prior wind loading. 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

Avalanche Problem 2: Loose Dry

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New dry snow atop smooth firm bed surfaces may present a loose dry problem today. Also called sluffs, loose dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Though usually harmless, they could carry an unsuspecting skier into undesirable terrain. Be prepared for this problem on slopes greater than 35 degrees in areas unaffected by the wind.

Advisory Discussion

Spring will have to take a snowcheck for the time being. New snow and wind provide for heightened avalanche danger today on Mount Shasta. Cold, low density snow sits on top of old, icy bed surfaces. Most accumulation occurred yesterday evening and last night. Tip-toe through the terrain today and be wary of committing to skiing and/or riding steep slopes. Cold temps and wind should continue.

Recent Observations

Snow began to fall yesterday at 10 am. Near steady precipitation remained until midnight last night. In that period, .78 inches of snow/water equivalent was recorded at treeline on Mount Shasta, which translated into 9 inches of new, low density snow. Winds have averaged 17 mi/hr with gusts to 50 mi/hr out of the SW until 1900 hrs and then reorganized out of the NW this morning. Temps have remained in the teens. Conditions on the mountain yesterday were wintery. Poor visibility below treeline lead to whiteout conditions above treeline. At 2:30 pm, 2-3 inches of dry snow and graupel was observed with light to moderate southerly winds near and below treeline. New snow sits on top of  firm, widespread rain/melt freeze crust. Above treeline snow observations have not been verified. 

Weather and Current Conditions

Weather Summary

Yesterday's cold front moves off to our east this morning and colder air has moved in behind it. Moist, ohshore flow will continue and light, scattered showers are possible this morning. Once that warm April sun pops out, snow accumulation will melt quickly. Things will quiet down tonight as a weak upper ridge moves overhead. It's going to be dry Friday night and Saturday. Sunday, another front moves in bringing more wind to the usually windy areas. It will be followed by unseasonably low snow levels Sunday night into early next 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) 29 29 46 37.5 2 N
Sand Flat (6750 ft) station down
Ski Bowl (7600 ft) 13.5 13.5 28 22.5 82.3 8.6 0.78 0.4
Gray Butte (8000 ft) 12.5 12 27 21.5 17 49 NW
Castle Lake (5870 ft) 0 0 0 0 0 0 0 station down
Mount Eddy (6509 ft) 16 16 34 25.5 1 9 44.1 8.8 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
  Thursday Thursday Night Friday
Weather Mostly cloudy. Chance of precipitation 50%. Mostly cloudy. Chance of precipitation 20%. Not as cool, mostly cloudy in the AM becoming partly cloudy
Temperature (°F) 33 22 47
Wind Direction W W N
Wind Speed (mi/hr) 10-15 10-15 5-10
Expected Snowfall (in) .5-1 0 0
For 9000 ft to 11000 ft
  Thursday Thursday Night Friday
Weather Snow showers likely, mainly after 11am. Mostly cloudy and increasing winds. Wind chill values as low as -25. Chance of precipitation is 60%. A 20 percent chance of snow showers before 11pm. Mostly cloudy with decreasing winds. A 20 percent chance of snow before 11am. Partly sunny and windy. Wind chill values as low as -10.
Temperature (°F) 14 14 25
Wind Direction W NW NW
Wind Speed (mi/hr) 30-40 30-40 15-25
Expected Snowfall (in) 1-2 0 0

Season Precipitation for Mount Shasta City

Period Measured (in) Normal (in) Percent of Normal (%)
From Oct 1, 2017 (the wet season) 17.80 36.68 49
Month to Date (since Oct 1, 2018) 1.85 1.22 152
Year to Date (since Jan 1, 2018) 11.97 21.47 56

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.