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Avalanche Advisory for 2017-01-13 06:40:12

  • EXPIRED ON January 14, 2017 @ 6:40 am
    Published on January 13, 2017 @ 6:40 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest

Below treeline LOW avalanche danger exists while MODERATE danger near and above treeline continues for the possibility of human triggered wind slab avalanches. Wind slabs have been stubborn to trigger, however have the potential to be large and devastating to human life. Pay attention to who is above you, ski one at a time in avalanche terrain and don't group up in run out zones. Blue skies does not mean you get to let your guard down.

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.

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Avalanche Problem 1: Wind Slab

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Another day of sun has helped improve overall stability of the snowpack, however, temperatures have remained below freezing in much of the forecast area. Yesterday on Mt Shasta, wind slabs were noted on all aspects near and above treeline and some of them very large and scary looking. That said, there were some bold lines skied and sledders were out and about testing slopes whether they were aware of it or not and we had no resulting action. I would certainly not let your guard down and continue to use caution. The January storm track brought feet of new snow and west/southwest winds to the mountain for many days on end.

Keep your feelers out for not only older wind slabs, but also new wind slabs as well, all aspects, near and above treeline. Triggering a wind slab may be difficult. That said, multiple riders on a slope or the sweet spot near the thin edge of a wind slab could do the trick. Slabs could be several feet thick and will likely break at the first density change in the snowpack and/or could step down to deeper layers. Any wind slab avalanches that occur would likely be hard slabs and large in size. Natural avalanches are not expected, human triggered avalanches are possible albiet stubborn to trigger.

 

Avalanche Problem 2: Cornice

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Small to large cornices have been observed within the forecast area over the past several days. Cold temperatures could keep cornices sensitive to trigger. Cornices can often trigger avalanches on slopes below. Identify terra firm by observing rocks, twigs, trees and other signs of earth below your feet. If you find yourself tip-toeing out to the edge of a ridgeline/cornice to fulfill your inner daredevil, you may find yourself taking the elevator drop, becoming swept off your feet and down into undesireable terrain. Stand back!

Forecast Discussion

This will be day 3 of clear weather and the snowpack continues to settle and stabilize. Our persistent weak layer is a thing of the past and current concerns lie within stubborn, but potentially large wind slab avalanches near and above treeline. We've had a ton of new snow and a lot of wind. Wind slab galore has been observed on the mountain, all of them still sitting in place... which is a little disconcerting. As mentioned, a few bold skiers and riders have been "testing" slopes to no avail, which is good... but we are still a little leery.  Folks will continue to branch out onto steeper and higher terrain on the mountain as tracks get layed down. Stay on your game. A snowmobile or multiple skiers on a slope could trigger a large, hard wind slab. These can pop without any warning and lead to a very bad day. For the superstitious ones...today IS Friday the 13th...

 

Recent Observations

Observations were made on the south side of Mt Shasta yesterday, Bunny Flat, Green Butte and the Old Ski Bowl area. A stark difference from the Castle Lake area from the day prior. While the Castle Lake experienced the widespread crust form over the top of the snowpack, cold, soft and buttery powder could be found out of the gate from Bunny Flat. This was the second solid day of clear weather and our first above treeline foray since the active January storm cycles. Numerous old avalanches were observed above treeline, all of which had occurred sometime within the most recent storms of several days ago. Most notable, the entire east aspect of Green Butte released a natural wind and/or storm slab.  While this avalanche did not run a great distance, it was very wide, probably about 1/2 mile or so. Also, some old activity was observed on the northwest aspect of Gray Butte. No current avalanches were observed. Snow surface conditions are remarkably smooth considering the strong west/southwest winds we had. Isolated pockets of wind erosional features, a few scoured and hard areas were noted, but overall smooth and soft snow conditions were found. Near and below treeline to about 6,900 feet held the best powder snow while above treeline had some great snow also, but a bit more variable with packed powder and some hard wind slabs here and there. Winds switched to east/northeast and visible blowing snow was present all day, however icy crystals were not condusive to rapid new wind slab growth. At NE facing, 9,000 ft snowpit location, a 35cm hard wind slab sat on top of lighter density snow. It was at this density change where all failures within tests took place.Moderate to hard failures produced clean shears at this layer within small and large column stability tests, however full propagation on a slope scale I feel would be tough, though not impossible. Multiple riders on a slope or near the edge of a wind slab could potentially trigger a small to large, hard wind slab. [See the "Green Butte/Old Ski Bowl 1.12.17" observation below for pit profile, photos and additional snowpack details.] 

Weather and Current Conditions

Weather Summary

A dry and cold air mass yields to a low impact period of weather over the forecast area. Blue sky, light winds and chilly temperatures can be expected today. Temperatures will slowly increase for the MLK weekend with full sun providing your Vitamin D. This will be a welcome reprieve from the wet and wild storms of weeks past... although powder hounds and drought monitors might disagree! Perhaps some have read our text or heard it elsewhere... indeed another atmospheric river event is forecasted for next week and models continue to align for this active wet pattern to start Monday night. Monday through Thursday, rainfall totals range from 3-7 inches with snow levels painfully high, 7,000 to 8,000 feet. South to southwest winds will be gale force on the mountain. Any break in the systems will be short lived. Now is the time to prepare and we will provide more details on all this as the weekend comes to a close.

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In Mt Shasta City at 0500, we have a current temperature of 20 F with clear skies.

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

Old Ski Bowl - 7,600 feet, the current temperature is 21 degrees F.  Temperatures have ranged from 11 F to 23 F. Snow on the ground totals 115 inches with a no new snow and 3 inches of settlement

Grey Butte - 8,000 feet, the current temperature is 20 degrees F. Temperatures have ranged from 13 F to 21 F.  Winds have averaged 20-25 mph with gusts to 35 mph, blowing out of the east/northeast.

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

Castle Lake - 5,600 feet, the current temperature is 20 degrees F. Temperatures have ranged from 18 F to 25 F. Snow on the ground totals 56 inches with no new snow and 2 inches of settlement.

Mt Eddy - 6,500 feet, the current temperature is 14 degrees F. Temperatures have ranged from 11 F to 23 F. Snow on the ground measures 63 inches with no new snow and 2 inches of settlement.  Winds have averaged 2-3 mph with gusts to 7 mph, blowing out of the southwest.

THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 28.27 inches of water, normal is 18.10 inches, putting us at 156% of normal.  For the month of January and for the year of 2017, we received 7.11 inches of water, normal is 2.89 inches, putting us at 246% 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.

CURRENT CONDITIONS at Bunny Flat (6950 ft)
0600 temperature: 10
Max. temperature in the last 24 hours: 26
Average wind direction during the last 24 hours: East/Northeast
Average wind speed during the last 24 hours: 0-5 mi/hr
Maximum wind gust in the last 24 hours: 10 mi/hr
New snowfall in the last 24 hours: 0 inches
Total snow depth: 66 (-2) inches

Two Day Mountain Weather Forecast

Produced in partnership with the Medford NWS

For 7000 ft to 9000 ft
  Friday
(4 a.m. to 10 p.m.)
Friday Night
(10 p.m. to 4 a.m.)
Saturday
(4 a.m. to 10 p.m.)
Weather Sunny Partly cloudy Mostly sunny
Temperature (°F) 33 23 39
Wind (mi/hr) Northeast 5-10 East/Northeast 0-5 East/Northeast 5-10 mph
Precipitation SWE / Snowfall (in) / 0 / 0 / 0
For 9000 ft to 11000 ft
  Friday Friday Night Saturday
Weather Sunny. Blustery. Partly cloudy Mostly sunny. Blustery.
Temperature (°F) 23 23 27
Wind (mi/hr) Northeast 10-15 mph Northeast 0 North/Northwest 5-10 mph
Precipitation SWE / Snowfall (in) / 0 / 0 / 0

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.