Grand Mesa
AvalancheDylan Craaybeek, Jewell Campbell · Feb 22, 2023 · Grand Mesa
Weather
Warm morning (39F in Carbondale at 8:00, 49F in Rifle at 9:00, 33F at the trailhead around 7800 ft.) with Broken sky coverage, no precipitation, and Moderate winds. S-1 until around 10:00 then S5 and Strong winds for about two hours. Snow remained between S2 and S5 for the remainder of the day and winds remained Strong with Extreme gusts and Intense but sporadic snow transport inefficiently loading terrain features that may not usually see wind-loading at all elevation bands.
Snowpack
Average height of snow is about 200 to 250cm on northerly and easterly slopes with 15 to 30cm of new snow and and quickly increasing with snowfall rates between S2 and S5 all day. There are two persistent weak layers (PWL) near the surface of the old snowpack prior to this storm around 50 and 80cm deep. The upper PWL is the most concerning layer in the snowpack for avalanches with extended column tests showing propagating results between 10 and 20 taps and propagation saw tests getting propagating failures after cutting through about 20-25% of the column. This concern was validated after seeing a very recent natural avalanche fail on this layer and propagate several hundred feet across a terrain feature. The new snow seems to be bonding well to the old snow surface aside from a spatially variable graupel layer lower down in the storm snow that was mostly found below the treeline and not above 10,000ft.
Avalanche
Observed one large natural avalanche on a gully terrain feature that wraps from southeast through east to northeast. The avalanche broke on a layer of rounding facets 1.5mm in size. The crown face of the avalanche was about 50cm deep on average and broke on a 36-39 degree slope. The debris ran farther down the gully feature than we could see, at least 500 vertical feet.