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Avalanche Advisory for 2017-01-14 07:03:54

  • EXPIRED ON January 15, 2017 @ 7:03 am
    Published on January 14, 2017 @ 7:03 am
  • Issued by Andrew Kiefer - Mt Shasta Avalanche Center

The avalanche danger is MODERATE above treeline.  LOW avalanche danger exists near and below treeline.  On all aspects near and above treeline, wind slabs and cornices are the avalanche problems for today.  Triggering stubborn wind slabs or cornices remains possible for backcountry travelers, and an avalanche event in these conditions would likely pose significant consequences for anyone involved. Evaluate snow and terrain carefully today, and 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.

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

Avalanche Problem 1: Wind Slab

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Wind slabs remain the primary avalanche concern and have the potential to exist on all aspects near treeline and above treeline.  Human triggered wind slab avalanches are possible, and naturally triggered wind slabs are unlikely.  Wind slabs that formed during our most recent storm are now hard slabs that are several feet thick.  These lingering wind slabs pose a low likelihood, high consequence scenario for backcountry travelers, especially in upper elevation terrain.  It may be difficult to trigger an old wind slab, but if a wind slab avalanche occurs, it would likely be large and dangerous.   In addition, new wind slab formation continues as snow is available for transport, and variable winds redistribute snow unevenly throughout the terrain.  Practice good travel techniques, and only expose one skier or rider at a time to avalanche terrain.  Regroup in islands of safety, and be aware of what is above you and below you.  Use visual observations to identify the wind slab problem, and avoid slopes 35 degrees and steeper holding wind loaded snow.  

Avalanche Problem 2: Cornice

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Cornices formed during our most recent storm event, and exist on ridgelines and exposed terrain features near and above treeline on all aspects.  Cornices are dangerous snow formations that are often overhung, and can break in very unpredictable ways.  Today, a falling cornice also has the potential to trigger a wind slab on slopes below.  Be sure to stand back, and give overhung cornices plenty of space.  Evaluate slopes that are threated by cornices from above, and watch for warming temperatures and solar radiation input throughout the day to increase the likelihood of cornice failure.  

Forecast Discussion

It has been 4 days since our advisory area has received any precipitation, and clear and sunny weather looks to continue for now.  Overall, our snowpack has adjusted well to the added weight of the recent storms, and stability is improving.  Variable conditions do exist in the backcountry, however.  Elevations 6000ft and below likely hold a stout, breakable crust, and evidence of the 01/08 rain on snow event is widespread.  Above this elevation, cold powder snow exists, providing very good skiing and riding conditions.  Upper elevation terrain holds the greatest potential for avalanches.  Today, snowpack assessment should target the wind slab and cornice problems.

Recent Observations

Over the past few days, no avalanches occurred, and no significant signs of instability have been observed. During an outing up the South Fork Rd. and in the Cliff Lakes area yesterday, a 2-5cm breakable rain crust was found as the snow surface condition up to the 6000ft level.  Large and deep rain runnels were widespread up to this elevation as well.  The recent calm, cold, clear nights have allowed for patches of surface hoar to form on all aspects up to 7000ft in this area.  Trees, as well as the snow surface, experienced significant riming in the near and above treeline elevation bands.  Small to large cornices were found along easterly facing aspects of ridgelines.

A test pit dug yesterday on a NNE slope at 6500ft revealed 80cm of settled dry snow resting on the 01/08 rain crust.  Small column tests failed on a density break 25cm down within the top 80cm of the snowpack.  Large column tests did not produce propagating failures.  Small loose dry/sloughing occurred while skiing steeper slopes, but were not large enough to pose a significant concern to backcountry riders.  Ski quality was very good above the 6000ft level where the snow surface remained cold and dry.

Weather and Current Conditions

Weather Summary

A ridge of high pressure is in place over the advisory area, and relatively quiet weather will continue through Monday.  Any lingering overnight clouds will clear out this morning, and skies will be sunny today.  Northeast winds are expected, blowing 5-10 mph, with 20-25 mph gusts at upper elevations.  Freezing levels will be near 5000ft today and tomorrow, and will rise to 8000ft on MLK Day.  A weak disturbance offshore will move near the forecast area today, but is only expected to result in partly cloudy skies tonight.  By late Monday night, a frontal boundary will reach the area, making Tuesday our next chance for precipitation.  7000-8000ft freezing levels will bring a mix of rain and snow.  This warm and wet atmospheric river event should last through Thursday.

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In Mt Shasta City at 0500, we have a current temperature of 25 F with clear skies.

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

Old Ski Bowl - 7,600 feet, the current temperature is 33 degrees F.  Temperatures have ranged from 21 F to 33 F. Snow on the ground totals 114 inches with a no new snow and 1 inch of settlement

Grey Butte - 8,000 feet, the current temperature is 27 degrees F. Temperatures have ranged from 21 F to 39 F.  Winds have averaged 15-30 mph with gusts to 42 mph, blowing out of the east/northeast.

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

Castle Lake - 5,600 feet, the current temperature is 27 degrees F. Temperatures have ranged from 18 F to 30 F. Snow on the ground totals 55 inches with no new snow and 1 inch of settlement.

Mt Eddy - 6,500 feet, the current temperature is 22 degrees F. Temperatures have ranged from 13 F to 31 F. Snow on the ground measures 62 inches with no new snow and 1 inch of settlement.  Winds have averaged 1-3 mph with gusts to 5 mph, blowing out of the west/southwest.

THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 28.27 inches of water, normal is 18.34 inches, putting us at 154% of normal.  For the month of January and for the year of 2017, we received 7.11 inches of water, normal is 3.13 inches, putting us at 227% 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: 17
Max. temperature in the last 24 hours: 30
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: 65 inches

Two Day Mountain Weather Forecast

Produced in partnership with the Medford NWS

For 7000 ft to 9000 ft
  Saturday
(4 a.m. to 10 p.m.)
Saturday Night
(10 p.m. to 4 a.m.)
Sunday
(4 a.m. to 10 p.m.)
Weather Sunny Mostly cloudy Mostly sunny
Temperature (°F) 33 22 40
Wind (mi/hr) East/Northeast 5-10 East/Northeast 0-5 North/Northeast 5-10 mph
Precipitation SWE / Snowfall (in) / 0 / 0 / 0
For 9000 ft to 11000 ft
  Saturday Saturday Night Sunday
Weather Sunny. Blustery. Partly cloudy and Blustery, then Mostly Cloudy Partly Sunny, then Mostly Sunny and Blustery.
Temperature (°F) 23 24 32
Wind (mi/hr) North 20-25 mph North/northwest 0 Northeast 20-25 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.