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Avalanche Advisory for 2017-04-14 06:37:49

  • EXPIRED ON April 15, 2017 @ 6:37 am
    Published on April 14, 2017 @ 6:37 am
  • Issued by Aaron Beverly - Mount Shasta Avalanche Center
  • April 14, 2017 @ 6:37 am

    Advisory Hotline: (530) 926-9613

  • Avalanche danger is CONSIDERABLE above treeline and MODERATE near treeline. Wind slabs remain a concern and may continue to grow at higher elevations. Excercise caution when approaching slopes greater than 35 degrees. Cornice falls are also a concern. Stay off of slopes under large overhanging cornices today. Avalanche danger below treeline is LOW.

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

Avalanche Problem 1: Wind Slab

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Wind slabs remain a concern near and above treeline. Winds reached 20 mph out of the west and northwest yesterday. Recent slabs may be encountered on east and southeast facing slopes. Older slabs that formed since Tuesday would exist mainly on NW-N-NE aspects. With light winds predicted today, slabs are unlikely to grow in size. But always pay attention. Blowing snow and textured snow surfaces are indicators of current or recent wind loading. Wind slabs will most likely be triggered on leeward slopes 35 degrees and steeper that are unsupported, have a convex shape, or that are just below ridgelines. 

Avalanche Problem 2: Cornice

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Cornice triggered avalanches large enough to kill or bury a person were seen in the Castle Lake area yesterday afternoon. These corresponded with warm temperatures and plenty of solar radiation. With an overnight freeze and cloudly weather expected, these may be less of an issue today, but it would be best to stay clear of steep slopes with large overhanging cornices.

Advisory Discussion

No signs of a storm slab problem have been seen and with a spike in above freezing temperatures yesterday followed by a hard freeze last night, the snow pack should be locked up tight below treeline in most places.

Wind slabs may remain a problem in isolated areas near treeline. In the Castle Lake area, it will be hard to find this problem due to a widespread melt-freeze event. Above treeline, where temperatures have remained cold, the wind slab issue may persist. Though winds are expected to be light today, snow is still available for transport and slabs could grow if the wind picks up. It is best to continue to exercise caution when approaching slopes greater than 35 degrees where wind loading is evident. Evaluate the snow pack carefully.

A new concern today and tomorrow will be cornice falls. Three natural cornice triggered avalanches were observed yesterday at Castle Lake, one observed in action. It was not certain if these were wind slab or wet loose avalanches, but enough snow was entrained along their path to bury a person. It would be best to keep away from steep slopes under large overhanging cornices today.

We will issue our last avalanche advisory of the season this Sunday, April 16th.

Recent Observations

The Castle Lake area received quite a bit of sun yesterday with daytime highs reaching 51 degrees F around 3:00 p.m. Hundreds of small rollerballs were seen originating along cliff faces in west facing terrain. Small point releases and small shallow wind slab avalanches were also observed on sun exposed aspects.

Two cornice triggered avalanches were observed along the bowl of Middle Peak. While taking pictures of the debris, a third one released. See pictures and video in the posted observation.  A good reminder: recent avalanche activity is a red flag for avalanche danger!

Solar radiation and warm temperatures were probably the cause of these avalanches. The top several inches of snow througout the basin was wet and easily penetrable with a ski pole.

Temperatures quickly dropped after the avalanche event. Overnight temperatures at the Castle Lake weather station have been in the low 20's.

Mount Shasta did not receive the same warming event. It was covered in clouds all day and daytime highs at Grey Butte reached 33 degrees F briefly. Winds peaked at 21 mph out of the northwest. A little over an inch of new snow was received above 6000 feet. The snowpack settled 3 inches.

Current Conditions at Bunny Flat (6950')

0600 temperature: 18 deg. F.
Maximum temperature in the last 24 hours. 36 deg. F.
Average wind direction during the last 24 hours. West, northwest
Average wind speed during the last 24 hours. 12-22 mph
Maximum wind gust in the last 24 hours. 42 mph
New snowfall in the last 24 hours. 1 inches
Total snow depth. 135 inches

Weather

A moist westerly flow will continue to produce some showers today but no snow accummulation is expected. Daytime temperatures could rise into the lower forties at mid-elevations.  We might see some sun this morning but expect mostly cloudy weather for most of the day until tonight.

Dryer, warmer, clearer conditions will prevail tomorrow. If you are looking for a day to enjoy the last weekend at the Mount Shasta Ski Park, tomorrow will be the day. Unsettled weather is likely to return Sunday afternoon.



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In Mt Shasta City at 0500, we have a current temperature of 26 F

On Mt Shasta (South Side) in the last 24 hours...

Sand Flat - 6,750 ft. The current temperature is 18 degrees F. Temperatures have ranged from 18 F to 36 F. Snow on the ground totals 135 inches with 1 inch of new and 3 inches of settlement.

Old Ski Bowl - 7,600ft. The current temperature is 10 degrees F. Temperatures have ranged from 10 F to 36 F. Snow on the ground totals 220 inches with 2 inches of new and 3 inches of settlement.

Grey Butte - 8,000 feet. The current temperature is 12 degrees F. Temperatures have ranged from 12 F to 33 F. Winds have ranged from 12-22 mph with gusts to 42 mph, blowing from west and northwest.

Mt Eddy Range (West side of Interstate-5)... 

Castle Lake - 5,800 feet. The current temperature is 20 degrees F. Temperatures have ranged from 20 F to 52 F. Snow on the ground totals 115 inches with no new snow and 3 inches of settlement.

Mt Eddy - 6,500 feet, the current temperature 15 degrees F. Temperatures have ranged from 15 F to 34 F. Snow on the ground measures 110 inches with no new and 7 inches of settlement. Variable winds have averaged 2 mph with gusts up to 8 mph.

THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 56.44 inches of water, normal is 36.87 inches, putting us at 153% of normal. For the month of April, we have received 6.98 inches of water, normal is 1.41 inches, which is 495% of normal. And finally for the year of 2017, we received 35.28 inches of water, normal is 21.66 inches, putting us at 163% of normal.

Always check the weather before you attempt to climb Mt Shasta. Further, monitor the weather as you climb. Becoming caught on the mountain in any type of weather can compromise life and limb. Be prepared.

 

Two Day Mountain Weather Forecast

For 7000 ft. to 9000 ft.
  Friday Friday Night Saturday
Weather A 20 percent chance of snow showers. Partly sunny. Mostly cloudy. Mostly sunny.
Temperatures Mid 30s - lower 40s deg. F. Lower to mid 20s deg. F. Mid 40s - lower 50s deg. F.
Wind direction West Northwest then northeast Northeast then southeast
Wind speed 5-10 mph 5 mph 5 mph
Expected snowfall 0 in. 0 in. 0 in.
For 9000 ft. to 11000 ft.
  Friday Friday Night Saturday
Weather A 20 percent chance of snow showers. Partly sunny and cold. Mostly cloudy. Mostly sunny. Breezy.
Temperatures 12 deg. F. 21 deg. F. 25 deg. F.
Wind direction West West South
Wind speed 8-14 mph 10-12 mph 17-23 mph
Expected snowfall 0 in. 0 in. 0 in.

Disclaimer

This advisory does not apply to Ski Areas or Highways and is for the Mt. Shasta, Castle Lake and Mt. 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.