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Avalanche Advisory for 2017-01-04 06:51:17

  • EXPIRED ON January 5, 2017 @ 6:51 am
    Published on January 4, 2017 @ 6:51 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest

Wind slabs, storm slabs and persistent slabs present a complex mix of avalanche problems today. Dangerous avalanche conditions exist in the backcountry. Expect MODERATE danger below treeline and CONSIDERABLE to HIGH danger near and above treeline. Natural avalanche are likely in some areas. Human triggered avalanches are very likely. Stay off avalanche terrain and out of runout zones. Very careful snowpack evaluation, cautious route finding, and conservative decision-making are essential today.

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

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.

Avalanche Problem 1: Wind Slab

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Natural avalanches are likely today and human triggered avalanches are very likely. Moderate southwesterly winds have remained consistent over the course of the storm, blowing in combination with 2 feet of fresh snow on the ground. Winds will continue today, southwesterly in nature. Wind slabs will remain sensitive to trigger and could be 2-6 feet deep. This problem is most likely to be found near and above treeline on NW-N-NE-E-SE facing slopes but could be found in more isolated areas on other aspects or below treeline. Loaded slopes steeper than 35 degrees could produce small to large scale avalanches.

Numerous clues such as drifting snow, cornices, and wind pillows exist to identify areas of recent wind loading and subsequent wind slab formation. Identify and avoid areas where wind slabs are likely to exist.

Avalanche Problem 2: Storm Slab

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Several feet of new snow accumulation has rapidly fallen on a variety of old snow surfaces from firm, icy slopes, crusts, wind scoured sastrugi features and colder powder snow. Failure within the snowpack associated with this problem is possible at the old snow/new snow interface or anywhere within the new storm snow. Warming temperatures is expected to increase the upside down configuration (heavier snow on top of ligher snow) of the snowpack. This avalanche problem is most likely to be found below and near treeline in wind protected areas on all aspects.

Avalanche Problem 3: Persistent Slab

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On 12/23, a weak layer was buried by our last storm event, and now exists on cold, shady aspects (NW-N-NE-E) throughout the advisory area.  This layer exists as rounding facets and is now buried by 2-4 feet of new snow. In many locations, this layer has been found to sit below a crust.  No avalanches have occurred on this layer.  Recent stability tests targeting this layer have been inconsistent, but have shown unstable results.  

As new snow continues to increase the load on the snowpack, large persistent slab trending to deep slab avalanches are an increasing concern. Any avalanches that either initially fail on or step down to this weak layer will be large and destructive. Recent snowpit data has shown variability on the degree of weakness in this layer from one location to another, but it is still a problem. This problem is possible on NW-N-NE-E aspects near treeline and some areas below treeline.

Forecast Discussion

The Mt Shasta area backcountry has been under seige of a potent winter storm that has brought over 2 feet of new snow over a 48 hour period. If an avalanche cycle has not already occured overnight, it is primed for today. Numerous signs of instability were presented to backcountry travelers yesterday and a mix of wind slabs, storm slabs, persistent slabs and even some potential loose-dry avalanche problems exist in the backcountry. 

We don't need to elaborate... Rapid accumulation of new snow, consistent wind speed/direction, recent avalanches, cracking and whoomphing in the snowpack.... these are all signs of considerable to high avalanche danger. Stay off of avalanche terrain and clear of runout zones today folks!

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LOCAL AREA ROAD, NORDIC, AND SNOWMOBILE PARK STATUS:

The Sand Flat cross country ski trails are in good shape and ready for your cross country skis and snow shoes.  These are backcountry routes marked with blue diamonds on trees.  Trails are not groomed.  Snow shoers, please blaze a parallel trail to cross country skiers staying out of the skin track.  These trails can be accessed via the Everett Memorial Highway.  Thank you, and enjoy!

The Mt. Shasta Nordic Center is OPEN for the season! Take advantage of this wonderful venue. Groomed trails accomodate both classic and skate skiing styles. Rentals available. Visit their website for more details.  http://www.mtshastanordic.org

The Pilgrim Creek & Deer Mountain Snowmobile Parks are open, however there is no snow at these locations currently. One must drive down the 19 road (Military Pass) for several miles to get to consistent snow before unloading. Private industry is logging out there so watch out for log trucks. Head to our "Education" tab on our website and find the snowmobile section for trail information, grooming status, and other sledder resources.

The Castle Lake Road is OPEN. The Everett Memorial Highway is OPEN. The Castle Lake and Everett Hwy are plowed year round to the trailheads. The roads are not always first priority, so your dawn patrol powder mission might be ceased if the plow has not made it up yet. Siskiyou County does a great job keeping the roads clear. Be respectful of the plow drivers if you encounter them. If you get to Bunny Flat before or during when the plow is there, please park on the uphill, LEFT side of the parking lot as you drive in. This is uphill and lookers right of the bathrooms. Thank You!

The Five Red Flags of Avalanche Danger any time of year include: 1) Recent/current avalanche activity 2) Whumphing sounds or shooting cracks 3) Recent/current heavy snowfall 4) Strong winds transporting snow 5) Rapid warming or rain on snow.

Recent Observations

We've had a storm total of about 2 feet over the forecast area over the past 48 hours with moderate west/southwest winds.

Observations made on the east side of Mt Shasta in the Ash Creek Butte area noted cracking within soft wind slabs on a north/northeast aspect, collapsing of the snowpack, wind loading and easy cornice failures.

Observations up on the west side of the forecast area in the Castle Lake zone found an easily triggered storm/wind slab (see observation with picture) within new snow layers which subsequently stepped down to old snow interface.

Observations up on the south side Mt Shasta near treeline found better stability with no avalanches, shooting cracks, or collapses observed (visibility was difficult).  The height of new snow ranged from 25-35cm between 7000-8500ft by 3pm. That has increased overnight.  The storm snow has an upside-down configuration with 20-30cm of dense snow sitting on top of 5cm of less dense snow.  On E-SE-S-SW-W slopes observed, the new snow was falling on firm wind scoured snow, supportable crusts up to 2cm thick, and breakable, eroded crusts. South, SW, and W winds were observed transporting snow continuously throughout the day near and above treeline.  Wind slab development and cornice formation was most noticeable above treeline on easterly aspects.

Numerous handpits on E-S-W aspects and two test pits dug on SE and E aspects near and below treeline conveyed that the storm snow was just beginning to show slab characteristics.  Small column tests showed the majority of failures occurring within the storm snow on the density break 20-30cm down from the snow surface.  Failures also occurred at, and directly below a crust present in many locations as the new/old interface.  No propogation occurred in large column tests. 

 

 

Weather and Current Conditions

Weather Summary

A robust storm has left the North State cloaked in a thick white coat of beautiful, light snow this morning. This system continues to move west to east and is not done with us yet. Compared to what we just experienced, new snow accumulation today will be small potatoes, though lingering snow showers will bring another 2-4 inches of snow to the backcountry. Temperatures have warmed this morning, about 8 degrees warmer than yesterday at this time. Precipitation should be clear of the area by Thursday morning. A break in the storm action will ensue for Thursday, but don't put away your snow blowers yet...another potential atmospheric river event is queing up for this weekend. So, expect increasing clouds later in the week (Friday) with another strong system on tap for the weekend.

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In Mt Shasta City at 0500, we have a current temperature of 34 F.

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

Old Ski Bowl - 7,600 feet, the current temperature is 22 degrees F.  Temperatures have ranged from 15 F to 22 F. Snow on the ground totals 91 inches with 16 inches of new snow. 

Grey Butte - 8,000 feet, the current temperature is 21 degrees F. Temperatures have ranged from 14 F to 21 F.  Winds have averaged 20 mph with gusts to 49 mph, blowing from the west/southwest.

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

Castle Lake - 5,600 feet, the current temperature is 28 degrees F. Temperatures have ranged from 21 F to 28 F. Snow on the ground totals 50 inches with 16 inches of new snow.

Mt Eddy - 6,500 feet, the current temperature is 27 degrees F. Temperatures have ranged from 18 F to 27 F. Snow on the ground measures 55 inches with 13 inches of new snow.  Winds have averaged 2 mph with gusts to 11 mph, blowing from the south/southwest.

THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 22.33 inches of water, normal is 15.92 inches, putting us at 140% of normal.  For the month of January and for the year of 2017, we received 1.17 inches of water, normal is .71 inches, putting us at 164% 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: 27
Max. temperature in the last 24 hours: 27
Average wind direction during the last 24 hours: West/Southwest
Average wind speed during the last 24 hours: 15-20 mi/hr
Maximum wind gust in the last 24 hours: 40 mi/hr
New snowfall in the last 24 hours: 16 inches
Total snow depth: 57 inches

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 before 10am, then snow showers likely after 10am. Breezy. Chance of precipitation is 80%. A 20 percent chance of snow showers. Mostly cloudy Mostly sunny
Temperature (°F) 26 falling to 19 11 21
Wind (mi/hr) West/Southwest 10-15 mph East/Northeast 5 mph East/Northeast 5 mph
Precipitation SWE / Snowfall (in) / 1-3 / 0 / 0
For 9000 ft to 11000 ft
  Wednesday Wednesday Night Thursday
Weather Snow before 10am, then snow showers likely after 10am. Wind chill values as low as -25. Windy. Chance of precipitation is 90%. A 20 percent chance of snow showers. Mostly cloudy, with a low around 3. Wind chill values as low as -25. Windy. Mostly sunny, with a high near 15. Wind chill values as low as -15. Windy.
Temperature (°F) 13 falling to 7 3 15
Wind (mi/hr) West/Southwest 40-50 mph West/Northwest 2-4 East/Northeast 10-15 mph
Precipitation SWE / Snowfall (in) / 2-4 / 0 / 0

Disclaimer

This advisory does not apply to Ski Areas or Highways and is for the Mt. Shasta, Castle Lake and Mt. Eddy back country. Use this information for guidance only. You may find different conditions in the back country and should travel accordingly. This advisory expires on midnight of the date it was posted unless otherwise noted.