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Avalanche Advisory for 2018-03-21 06:32

  • EXPIRED ON March 22, 2018 @ 6:32 am
    Published on March 21, 2018 @ 6:32 am
  • Issued by Aaron Beverly - Mount Shasta Avalanche Center

A potent storm will bring significant rain and snowfall over the next 24 hours. Avalanche danger will increase to CONSIDERABLE by tonight near and above treeline. Below treeline, avalanche danger will rise to MODERATE as falling rain and wet snow increases concerns for loose wet avalanches

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

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.

Forecast Hotline: (530) 926-9613

Avalanche Problem 1: Wind Slab

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Expect wind slabs to form near and above treeline by tonight near and above treeline. Strong to gale force winds will blow the 12-20 inches of expected snow onto leeward slopes. These slabs could be 2-4 ft thick. Human triggered avalanches are likely and natural avalanches are possible.

If you are brave enough to be out on Mount Shasta this afternoon and tonight, look for wind slabs in leeward terrain near and above treeline. Stick to protected or wind scoured areas to avoid the wind slab problem and steer clear of wind loaded slopes 35 degrees and steeper. Avoid runout zones.

Avalanche Problem 2: Loose Wet

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Tonight, elevations below 7500 ft could see over an inch of rain atop a few inches of new snow. This could lead to loose wet avalanches.

These avalanches typically occur within layers of wet snow near the surface of the snowpack. They start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage or catch backcountry travelers off guard.

Forecast Discussion

The incoming storm will begin upside down then finish right side up - a potential recipe for avalanches. Expect avalanche danger to increase and remain elevated throughout the week.

There is some uncertainty in the timing and snow amounts from this storm, but by all accounts this one looks to be a doozy. Remember the 5 red flags for avalanche danger:

  • Recent avalanche activity. 
  • Cracking, blocking or whooping
  • Significant snowfall in the last 24 Hours
  • Strong winds
  • Temperature rise

Recent Observations

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Snow began late Tuesday morning with snow levels near 4000 ft. Overnight, the Old Ski Bowl received between 2 and 3 inches of new snow. Winds have been southerly and light.

Breakable melt-freeze crusts predominate below treeline. Near treeline, snow surfaces are a mix of sun crusts, melt-freeze crusts, and settled dry snow.

No avalanches or significant signs of instability have been observed in several days.

Weather and Current Conditions

Weather Summary

All aboard for the Pineaple Express! An atomspheric river event will bring up to 3.25 inches of water by Sunday morning with the brunt it coming tonight and tomorrow. Snow levels should start near 5000 ft, then spike up to 7000 ft tonight, followed by a drop to 5000 ft and below Thursday. Expect several feet of snow above snow levels. Today and tonight could see up to 20 inches of snow at higher elevations.

Check out The California Weather Blog for more details about the Pineaple Express.

24 Hour Weather Station Data @ 5:00 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) 39 36 43 39.5 1 N
Sand Flat (6750 ft) station down
Ski Bowl (7600 ft) 28.5 23 29 27 74.2 2.5 0.28 0.5
Gray Butte (8000 ft) 27 21.5 27.5 25 7 25 SW
Castle Lake (5870 ft) 0 0 0 0 0 0 0 station down
Mount Eddy (6509 ft) 30.5 26.5 35.5 30.5 1 10 S 43.5 0.5 .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
  Wednesday
(4 a.m. to 10 p.m.) 		Wednesday Night
(10 p.m. to 4 a.m.) 		Thursday
(4 a.m. to 10 p.m.)
Weather Snow. Breezy. Chance of precipitation is 90%. Rain and snow, heavy at times. Windy. Chance of precipitation is 100%. Snow showers, heavy at times. Windy. Chance of precipitation is 100%.
Temperature (°F) 38 20 17
Wind (mi/hr) S 10-15 mi/hr S 20-25 mi/hr S 15-20 mi/hr
Precipitation SWE / Snowfall (in) / 3-5 / 3-4 / 4-7
For 9000 ft to 11000 ft
  Wednesday Wednesday Night Thursday
Weather Snow, heavy at times. Wind chill values as low as 11. Windy. Chance of precipitation is 100%. Snow, heavy at times. Wind chill values as low as 0. Windy. Chance of precipitation is 100%. Snow & snow showers, heavy at times. Wind chill values as low as 3. Windy. Chance of precipitation is 100%.
Temperature (°F) 28 23 24
Wind (mi/hr) S 30-35 mi/hr S 4-6 SW 45-50 mi/hr
Precipitation SWE / Snowfall (in) / 4-6 / 10-15 / 5-8

Season Precipitation for Mount Shasta City

Period Measured (in) Normal (in) Percent of Normal (%)
From Oct 1, 2024 (the wet season) 14.41 33.88 43
Month to Date (since Dec 1, 2024) 3.52 4.38 80
Year to Date (since Jan 1, 2024) 8.58 18.67 46

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.