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Avalanche Forecast for 2021-02-02 06:40

  • EXPIRED ON February 3, 2021 @ 6:40 am
    Published on February 2, 2021 @ 6:40 am
  • Issued by Ryan Sorenson - Mount Shasta Avalanche Center

Avalanche danger will remain CONSIDERABLE for near and above treeline today. Lingering wind slabs are likely on steep loaded terrain. Shifting winds out of the west and north will increase the distribution of wind slabs. MODERATE danger exists below treeline as warmer temperatures yesterday followed by colder temperature today has decreased the possibility of triggering large wind slabs at lower elevations.

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

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

  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
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    Small

Today's periods of light snowfall and productive moderate south/westerly winds will keep the likelihood of wind slab avalanches elevated. Yesterday and last night had productive moderate south winds with strong gusts. At our Old Ski Bowl weather station, we measured 6 inches of wet snow with 1 inch of snow water equivalent. This could equate to over a foot of new snow at higher elevations. Expect large wind slabs to linger on leeward terrain. Wind slabs will continue to increase in size and distribution today. Winds were primarily out of the south yesterday and are switching to the west and north.  Loaded NW-N-NE-E-S-SE aspects are most suspect for fresh and preexisting wind slabs. However, local topography variations can affect a slope's wind speed, direction, and loading characteristics.  Natural wind slab avalanches are possible, and human triggering likely on steep loaded terrain near and above treeline. Warmer temperatures yesterday followed by cooler temperatures today have decreased the likelihood of triggering at lower elevations. However, with more fresh snow and moderate winds today, human triggered wind slabs remain possible on steep loaded terrain below treeline. We haven't observed much wind effect below treeline but if you find colder leeward slopes be suspicious of lingering wind slabs. 

Use caution if you plan to step out into steeper, higher elevation terrain today. A level of uncertainty remains as low visibility has limited observations above treeline. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are necessary to avoid wind slab avalanches. Be willing to step back if you see shooting cracks or whoomphing within in the snowpack. 

Forecast Discussion

Small storm slabs may be possible on steep terrain late this evening if the storm materializes. Strom slabs release as a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. 

  • The Everitt Memorial Highway and Castle Lake road remain closed.
  • Snowmobiles have been launching from McBride Springs and riding up on the mountain in many prohibited motorized equipment areas. This behavior is not tolerated. See the map for a reminder of the boundaries. 

Recent Observations

On a quick jaunt up to Castle Lake yesterday, we observed moderate winds with strong gusts, blowing snow, and limited visibility. The snowpack is similar to what we have seen on the south side of Mount Shasta. Snow is right-side up ranging from 4F to 1F down to the hard melt-freeze crust from over a week ago.   A thin, breakable ice crust that formed on Saturday is a few inches below the snow surface.  Hard compression tests were able to produce failure on a density change below the ice crust. See observation for more details. 

Snowpack notes:

  • Temperatures increased with a brief break in the storm on Monday night and yesterday morning. Snow levels rose to 4,500 to 5,500 feet.
  • We've seen several inches of settlement in the snowpack, but received strong south winds and fresh snow yesterday afternoon and last night.
  • 24-hour total precipitation measured at treeline on Mount Shasta, as of this morning at 0500: 6 inches snow / 1.00 SWE (Snow-Water Equivalent) 
  • Gray Butte wind: moderate to strong has switched from southeast to west/southwest wind. Min and max winds speeds are 11 to 27 mi/hr,  and 17 mi/hr average.  Wind gusts were as high as 49 mi/hr.
  • Visibility has been poor for the past week, limiting the above treeline observations. 
  • It is unknown how prevalent or supportable the ice lense from Saturday is. 
  • Total snow heights:
    • 79.2 inches (201 cm) - 7,600 feet, Old Ski Bowl
    • 68.4 inches (172 cm) - 6,600 feet, Mt. Eddy
    • 62.3 inches (160 cm) - 5,800 feet, Castle Lake
    • 54.5 inches (138 cm) - 7,300 feet, Ash Creek Butte

Weather and Current Conditions

Weather Summary

Snow showers will linger this morning as we transition to a northerly flow (northwesterly winds) ahead of a mass of cold air pushing down from Canada. We can expect to pick up another 1 to 3 inches of snow accumulation today. Snow levels will stay above town (3,500 feet) then drop to 2,000 feet tonight and tomorrow. A quick-moving colder storm will impact the area tonight and tomorrow morning. Approximately 12 hours of snowfall will accumulate 5 to 8 inches by noon tomorrow. After that, a ridge of high pressure will bring dry and cold conditions until a week front skips by the northern reaches of our area Friday.

The NWS has issued a Winter Storm Warning above 3,500 feet and a Winter Weather Advisory above 3,000 feet until 10 a.m. this morning. 

24 Hour Weather Station Data @ 4:00 AM

Weather Station Temp (°F) Wind (mi/hr) Snow (in) Comments
Cur Min Max Avg Avg Max Gust Dir Depth New Water Equivalent Settlement
Mt. Shasta City (3540 ft) 39 36 42 39 3 ESE
Sand Flat (6750 ft) 30 28 32 30 0 0 0 1 snow sensor broken
Ski Bowl (7600 ft) 26.5 24 28.5 26 79.2 6 1 0
Gray Butte (8000 ft) 26 22.5 27.5 25 16 49 S
Castle Lake (5870 ft) 31 29 31.5 30 62.1 8 0
Mount Eddy (6509 ft) 29 26.5 31 28.5 3 9 SW 68.4 4.6 0
Ash Creek Bowl (7250 ft) 25.5 25.5 25.5 25.5 54.3 0 0
Ash Creek Ridge (7895 ft) 19 11.5 19 16.5 wind sensor now rimed

Two Day Mountain Weather Forecast

Produced in partnership with the Medford NWS

For 7000 ft to 9000 ft
  Tuesday
(4 a.m. to 10 p.m.)
Tuesday Night
(10 p.m. to 4 a.m.)
Wednesday
(4 a.m. to 10 p.m.)
Weather Mostly cloudy. Snow showers likely in the morning, then chance of snow showers in the afternoon. Snow level near 3,800 feet. Partly cloudy with a 60 percent chance of snow showers. Snow levels near 2,000 feet. Heavy snowfall before 11 a.m., then snow showers likely after 11 a.m. An 80 percent chance of snow showers. Snow levels near 2,000 feet.
Temperature (°F) 31 27 30
Wind (mi/hr) Southwest 15-20 South 10-15 Southwest 10-15
Precipitation SWE / Snowfall (in) 0.17 / 1-3 0.15 / 1-2 0.51 / 4-7
For 9000 ft to 11000 ft
  Tuesday Tuesday Night Wednesday
Weather Mostly cloudy. Snow showers likely in the morning, then chance of snow showers in the afternoon. Chance of snow, cloudy, windy. Mostly cloudy. Heavy snowfall likely in the morning, then chance of snow showers in the afternoon.
Temperature (°F) 16 8 11
Wind (mi/hr) Southwest 40-45 Southwest 30-35 West 30-35
Precipitation SWE / Snowfall (in) 0.17 / 2-3 0.15 / 1-3 0.51 / 5-8

Season Precipitation for Mount Shasta City

Period Measured (in) Normal (in) Percent of Normal (%)
From Oct 1, 2020 (the wet season) 12.41 22.51 55
Month to Date (since May 1, 2021) 0.97 0.24 404
Year to Date (since Jan 1, 2021) 8.83 7.30 121

Disclaimer

This forecast 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 forecast expires 24 hours after the posted time unless otherwise noted.