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Avalanche Advisory for 2017-12-03 06:59:23

  • EXPIRED ON December 4, 2017 @ 6:59 am
    Published on December 3, 2017 @ 6:59 am
  • Issued by Andrew Kiefer - Mt Shasta Avalanche Center

Shallow wind slabs have formed on NE-E-SE-S aspects near and above treeline on Mount Shasta. MODERATE avalanche danger exists above treeline, while the avalanche danger is LOW near and below treeline. Natural avalanches are unlikely, but small human triggered avalanches are possible on steep wind loaded slopes. Thin snow cover also poses a significant hazard for skiers and riders.  

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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Four to six inches of new snow overnight paired with moderate to strong northwest winds has created the potential for an isolated wind slab problem. Look for the presence of shallow wind slabs on leeward slopes near and above treeline, specifically, NE-E-SE-S slope aspects at 8000ft and above on Mount Shasta.

Forecast Discussion

A frontal system delivered modest snowfall amounts to higher elevation terrain yesterday and overnight, and now has moved well to the east of our advisory area. The recent snow paired with steady northwest winds has likely formed windslabs on leeward slopes in alpine terrain on Mount Shasta. At 7000ft and up, the new snow has fallen on a hardpacked and icy old snow surface. In addition to creating the potential for small wind slab avalanches, the new snow has hidden many shallowly buried objects. Thin snow cover is most likely the greatest hazard in the advisory area right now. In addition, wind scoured areas where the old snow surface is exposed will present extremely icy conditions, especially on Mount Shasta above 8000ft. A climb of the mountain in these conditions brings increased difficulty and consequence. 

As we start to venture out into the backcountry this early season, it is important to remember the basics. Always carry avalanche rescue gear and know how to use it. Work to improve your ability to identify avalanche terrain and watch for the 5 Red Flags of avalanche danger – Mother Nature’s obvious signs of snow instability:

*Recent Avalanches

*Wind Loading

*Heavy snow or rainfall

*Significant warming

*Signs of unstable snow (cracking or whumpfing)

Use all your resources. There is  a TON of info out there. Browse our avalanche tutorials and brush up on avalanche basics, maps, weather stations, recent observations, etc. Study up. Check your gear. Get dialed in. NOW is the time.

Recent Observations

Snowfall began yesterday afternoon and continued overnight, delivering 4-6 inches of new snow in areas 6000ft and above. A cooling trend has accompanied the recent storm as well as moderate to strong northwest winds. At 7000ft and higher, the new snow has fallen on very firm and icy old snow surfaces.

The existing snowpack prior to the recent storm is thin, very consolidated, and is well bonded to itself and the ground. No avalanches or signs of instability have been observed or reported so far this season. 

Mt Shasta:

< 6,000 feet : No snow

6,500 to 7,000 feet : Thin, patchy snowpack. Snow on the ground just begins in this elevation band. Firm, icy, dirty.

7,000 to treeline : Average snow depth of 50-90 cm, supportable, firm snow. Rocks, trees, shrubs, dirt patches, old ski and boot tracks

Above treeline: New snow rests atop firm, hard snow, variable coverage; rocks sticking out, completely scoured ridgelines; VERY ICY patches throughout above treeline terrain.  

Castle Lake:

Snow coverage is limited with less than a foot of snow on the ground. Castle Lake is not frozen.

Mt Eddy:

Snow coverage is limited with slightly more snow than Castle Lake, but this area does not have a usable snowpack yet.

Weather and Current Conditions

Weather Summary

This morning will bring mostly cloudy skies and a chance for lingering snowfall through 10am. Partly sunny skies and steady temperatures in the upper 20’s are expected this afternoon for the 6000ft level. Expect northwest winds to continue today and tonight with gusts ranging from 40-60 mph 8000ft and higher.

An upper level ridge of high pressure will build off the coast Monday and strengthen, bringing clear sunny weather for the remainder of the week. Daytime temperatures look to rise above freezing, while overnight lows will remain cold. December is a bit of a wild card in the long term. It's typically one of the wettest months, however at this point climate prediction models suggest below normal precipitation and above normal temps. 

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THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 5.72 inches of water, normal is 7.81 inches, putting us at 73% of normal. For the month of December, we received .18 inches of water, normal is .45 inches, which is 40% of normal. And finally for the year of 2017, we received 44.71 inches of water, normal is 35.81 inches, putting us at 125% of normal.

In Mt Shasta City at 0500, we have a current temperature of 32 F

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

Sand Flat - 6,750 ft, the current temperature is 21 degrees F. Temperatures have ranged from 21 F to 33 F. Snow on the ground totals 15 inches with 4 inches of new snow.

Old Ski Bowl - 7,600ft, the current temperature is 18 degrees F. Temperatures have ranged from 18 F to 31 F. Snow on the ground totals 25 inches with 6 inches of new snow.

Grey Butte - 8,000 feet, the current temperature is 15 degrees F. Temperatures have ranged from 15 F to 29 F. Winds have averaged 15-30 mph with gusts to 56 mph, blowing mostly from the west/northwest

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

Castle Lake - 5,800 feet, the current temperature is 23 degrees F. Temperatures have ranged from 23 F to 34 F. Snow on the ground totals 7 inches with 0 inches of new snow.

Mt Eddy - 6,500 feet, the current temperature 21 degrees F. Temperatures have ranged from 21 F to 34 F. Snow on the ground measures 11 inches with 4 inches of new snow. Winds have averaged 1-2 mph out of the west/southwest with gusts up to 13 mph.

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: 21
Max. temperature in the last 24 hours: 33
Average wind direction during the last 24 hours: West/Northwest
Average wind speed during the last 24 hours: 15-30 mi/hr
Maximum wind gust in the last 24 hours: 56 mi/hr
New snowfall in the last 24 hours: 4-6 inches
Total snow depth: 15 inches

Two Day Mountain Weather Forecast

Produced in partnership with the Medford NWS

For 7000 ft to 9000 ft
  Sunday
(4 a.m. to 10 p.m.)
Sunday Night
(10 p.m. to 4 a.m.)
Monday
(4 a.m. to 10 p.m.)
Weather Snow showers likely, mainly before 10am. Chance of precipitation is 60%. Then partly sunny. Partly Cloudy Sunny
Temperature (°F) 26 20 35
Wind (mi/hr) Northwest 15 North 15-20 North/Northeast 15
Precipitation SWE / Snowfall (in) / 0-1 / 0 / 0
For 9000 ft to 11000 ft
  Sunday Sunday Night Monday
Weather Snow showers likely, mainly before 10am. Then partly sunny. Wind chill values as low as -21. Windy. Snow showers, mainly before 10pm. Low around Partly cloudy and windy. Wind chill values as low as -16. Sunny and windy. Wind chill values as low as -9.
Temperature (°F) 13 12 25
Wind (mi/hr) North/Northwest 37-42 mph, increasing to 50-55 mph in the afternoon North 1-2 North/Norhteast 50 mph, gusting to 80 mph
Precipitation SWE / Snowfall (in) / 1-2 / 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.