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Touchy cornices and wind slabs at Castle Lake

Location Name: 
Castle Lake
Castle Lake
Date and time of observation: 
Fri, 02/19/2021 - 2:30pm
Observation made by: 
Red Flags:
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain

Location Map

96067 Mount Shasta , CA
United States
41° 13' 10.4412" N, 122° 23' 2.5296" W
California US

Snowpack Observations


A full circle tour of the Castle Lake Basin today. The forecast area saw breaks in precipitation over the past two days, but very little clearing. Today was very similar to yesterday: very poor visibility, moderate SW/W wind, snow flurries and touchy cornices and wind slabs along wind exposed ridgelines, bowls and moraines near and above treeline. Below treeline, the new snow kept itself together quite well with no obvious signs of avalanche danger presented. New snow amounts varied widely depending on topography: anywhere from 4 to 12 inches of new snow was measured. In calm, protected areas, about 4 - 6 inches seems to be about average. Near and above treeline where wind was present was the priority concern for the day. Cornices along the ridges were quite large and sensitive. I stomped on a few small ones but stayed well clear of the biggies. Cornices did not trigger wind slabs on slopes below.  Wind slabs were observed up to several feet thick, but were not as sensitive as the day prior on Mt. Shasta. Again, the most notable watch out's for the day was cornices along ridges and wind slabs on steep (>35 degrees), unsupported slopes. 

  • Observation Location: Castle Lake Basin
  • Elevation: 6,000 feet
  • Date: 20210219
  • Time: Afternoon
  • Observer: N Meyers
  • Sky Conditions:  Obscured (X), skies began to clear around 1600 hours.
  • Current Precipitation: Type -  SN, Rate - S1 - Flurries throughout the day, total accumulation 1-2 inches
  • Air Temperature: 36°F at 1100 hrs
  • Surface Penetration: Ski penetration (PS) = 5 in (12 cm), boot penetration (PF) = 10 in (25 cm)
  • Total Snow Depth (HS):  68 in (175 cm)
  • 24-hour New Snow Depth (HN24): 4-6 in (10-15 cm)
  • 24-hour New Snow Water Equivalent (HN24W): n/a
  • Wind Direction: SW | W
  • Wind Speed:  Moderate (M), 17-25 mi/hr, small trees sway
  • Column & Block Tests:
    • Slope Angle & Aspect ([]º, [N | NE | E | SE | S | SW | W | NW]:
    • ECTN12 ↓ 12 in (30 cm)


  • Near and above treeline along ridge lines, shooting cracks and cornices were easily triggered.
  • More shooting cracks, blocking within new snow.
  • More shooting cracks, blocking within new snow.
  • Visibility was very poor for most of the day.
  • A brief moment where the lake could be seen. This was rare.
  • A more typical view from the afternoon! Visibility was often less than 200 feet.
  • Looking downhill from snowpit dug near treeline.
  • Snowpit location, aspect, elevation near treeline in the Castle Lake Basin.
  • Snowpack layering at pit site
  • Extended column test at pit location
  • Evidence of wind loading from SW wind, a row of wind drifted snow behind this tree extending to the northeast.

Weather Observations


  • Very poor visibility
  • Moderate W/SW winds along higher terrain
  • Snow flurries throughout the day, total daytime snow accumulation 1-2 inches
  • Active wind loading on N/NE/E facing aspects
  • Ridges scoured to old snow surfaces


Cloud Cover: 
100% of the sky covered by clouds
Blowing Snow: 
Accumulation rate: 
Less than 1 in. per hour
Air temperature: 
Above Freezing
Air temperature trend: 
Wind Speed: 
Wind Direction: