22-23

Whumpf on Surface hoar at Hebgen

Hebgen Lake
Lionhead Range
Code
AS
Latitude
44.83810
Longitude
-111.34300
Notes
Went up Hebgen with a small gaggle of folks.  In and out visibility all day, with some occasional very light snow.  Dug first pit on the subtle ridge about 15 minutes from the top of the ridge, ENE aspect, about 8700 ft.  
HS = 135 cm
SH at 105 cm
ECTP6 on the SH
No other stability test results other than a broken ECTN25 sort of mid-pack (about halfway between the SH and the old DH layer)
 
Skinned up to the ridge and when we were almost to the top my partner was out front and triggered a noticeable whumpf.  Appeared to whumpf on the SH layer.  Whumpf was somewhat localized (about 10 m in diameter as a guesstimate). The group skied a short lap in the trees while I dug a pit for the whumpf study.  Pit profile attached.  Very similar structure to first pit, but also got an ECTP on the DH layer.  ESE aspect, 8950 ft.
HS = 135
SH at 105 cm, ECTP3
DH at 45 cm, ECTP23
Number of slides
0
Number caught
0
Number buried
0
Trigger
Skier
Images
Unstable Surface hoar at Hebgen
Hebgen Lake Snowpit Profile
Snow Observation Source
Unstable Surface hoar at Hebgen
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year
22-23

Skinned up to the ridge and when we were almost to the top my partner was out front and triggered a noticeable whumpf.    ESE aspect, 8950 ft.

HS = 135

SH at 105 cm, ECTP3

DH at 45 cm, ECTP23

Avalanche Details: Whumpf on Surface hoar at Hebgen
Forecast link: GNFAC Avalanche Forecast for Thu Jan 12, 2023GNFAC Avalanche Forecast for Fri Jan 13, 2023
Lionhead Range, 2023-01-12
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    • Unstable Surface hoar at Hebgen

    Date
    Activity
    Skiing
    Went up Hebgen with a small gaggle of folks.  In and out visibility all day, with some occasional very light snow.  Dug first pit on the subtle ridge about 15 minutes from the top of the ridge, ENE aspect, about 8700 ft.  
    HS = 135 cm
    SH at 105 cm
    ECTP6 on the SH
    No other stability test results other than a broken ECTN25 sort of mid-pack (about halfway between the SH and the old DH layer)
     
    Skinned up to the ridge and when we were almost to the top my partner was out front and triggered a noticeable whumpf.  Appeared to whumpf on the SH layer.  Whumpf was somewhat localized (about 10 m in diameter as a guesstimate). The group skied a short lap in the trees while I dug a pit for the whumpf study.  Pit profile attached.  Very similar structure to first pit, but also got an ECTP on the DH layer.  ESE aspect, 8950 ft.
    HS = 135
    SH at 105 cm, ECTP3
    DH at 45 cm, ECTP23
    Region
    Lionhead Range
    Location (from list)
    Hebgen Lake
    Observer Name
    Karl Birkeland

    Snowpit Test Results near Texas Meadows

    Date
    Activity
    Skiing

    Today on a west aspect around 7,835' in the Bridgers, near the top of Texas Meadows my party had test results of  CT28 (SC) and ECTP25 both at 20 centimeters up from the ground. Snow pits my party dug on other aspects in the area had unremarkable results.

    Region
    Bridger Range
    Location (from list)
    Texas Meadow
    Observer Name
    Meaghann Gaffney

    Surface hoar growth: Bradley Meadows

    Date
    Activity
    Skiing

    Observed widespread surface hoar growth (up to 2mm) along the Bradley Meadows uptrack. E-SE from 7400-7800’.

    Region
    Bridger Range
    Location (from list)
    Bradley Meadow
    Observer Name
    Dan Sandberg

    New Snow and Weak Layers in Lionhead

    Date
    Activity
    Snowmobiling

    We rode to ski hill first, and we dug a pit on the NE aspect near the top of the slide path. The HS was 160 cm (5 feet). We found buried surface hoar under the 10-12” of new snow, and we got an ECTN13 on this layer. Next we rode to the old weather station, and the HS was 5.5’. We found the surface hoar in this pit too, but it did not propagate during our ECT. Despite these two results, skiers near Hebgen Lake found the surface hoar layer, and they had an ECTP3 and 6 on that layer. They also noted an ECTP26 on depth hoar near the bottom of the snowpack. Although the surface hoar isn’t propagating on every slope in the Lionhead Range, it is possible for it to propagate on other slopes in the range. With this buried surface hoar and facets near the ground riders and skiers should continue to carefully assess the snowpack before stepping out into steeper terrain.

    Region
    Lionhead Range
    Location (from list)
    Ski Hill
    Observer Name
    Dave Zinn, Alex Haddad

    testing from Clarkston

    Date

    We skied up to 9230 on a south slope of Miller Ridge in sheep creek basin.  Intermittent clouds and sun, no wind.  Much wind affected snow, cross loading.  2-4 inches of fresh snow.    HS at 9000 was 100-110cm.  Started finding wind slab on rotten base at about 8900 then at 9200 where slope steepened we observed 3-5 foot shooting cracks and turned around.  Slope was 27-35.  Had climbed thru whitebark regrowth from 88 fire.  

    Back down at 8400', snowpack was very shallow and temp. was 32 degrees. 
    Observer Name
    Jim Test
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