April 2, 2023
April 3, 2023
Steve Mace | ESAC Forecaster
Zone or Region:
Mammoth lakes basin - Sensitive cornice features, reactive PWL
- I sampled several aspects and elevations in the lakes basin today. Dropping off the back side of the hill and traversing around from Fresno bowl I found some heavily wind-sculpted snow and a variety of stiff wind boards above 10000’. I did observe some areas of fresh wind load and some wind rolls held reactive wind slabs ranging in depth from 4-10”.
- Below 10000’ there was some minor surface warming but nothing I would consider a stability concern at mid-day. Solars here have not transitioned yet and the winds were ripping which I suspect was limiting the potential for concerning LW today.
- Some fresh fans of roller balls were observed in sheltered areas on NE-S aspects and surface snow in sheltered trees was moist and heavy. But no significant sluffs were observed.
- I dug in at 10100’ on a SE aspect where probing reviled the presence of a stiff crust at the 3/19 interface. This location had a thin but sensitive wind layer on the surface and stability tests highlighted the 3/19 interface as my layer of concern. I found near surface facets at this location that averaged around.5 mm with a max observed size of 1 mm. These grains showed some signs of rounding but still resulted in sudden planar results and propagation in my ECT test. (See pit profile for more details)
- On more northerly aspects above McCloud lake, I found several recent cornice features that were sensitive and recent wind loads ranging from thin and reactive to thicker and more stubborn.
- One cornice feature I broke loose was about 2’ deep at max and triggered a small wind slab on the slope below.
- I dug a second pit at 9800’ on an NW aspect and found a very different pack. The upper snowpack was very right side up in this location ranging from fist on the surface to 1f at the 3/19 interface. The MF crust at this location is very thin and breaking down making for a less obvious bed surface. But the combination of graupel and small near-surface facets still produced propagating results in my ECT test. (CT26 SP on. The 3/19 interface down 99 cm, ECTp 28 on the same layer)
- Two recent small avalanches were observed in the steep chutes near the Hollywood chute. These looked like broken cornice features that entrained some surface snow but it was hard to be sure.
- Winds were cranking today leading to significant transport along the crest and even in relatively protected areas BTL.
- Surface conditions ran the gamut today from high-quality orange peal to wet heavy pow, to wind boards and MF zippers. All in all a full value day in the Sierra!