TJ Trees Persistent Weak Layer

Toured up to the Mammoth Crest through the TJ Trees just E of TJ Bowl proper to see how the persistent weak layer was doing with the cold weather and new load. The facet layer is no longer moist, the grains are loose and dry again, and well developed (~3mm or more). The layer was observed from 9150' to 10,300' on W-NW-N-NE-ENE aspects and was consistently found between 50 and 70cm down from the surface. At 9150' on a 10 degree NW facing slope we heard and felt whumphing in approximately a 50' x 50' areas as the layer suddenly settled. 2 separate test sites showed both fracture initiation and propagation in the facet layer. Test site 1 (see photo): 1025am on a W facing large opening in the trees at 9800' with a snow depth of 105cm- CTE PC down 10cm in the F hard new snow, CTM SP down 20cm under the most recent (0119) 1F hard melt-freeze crust in in a layer of faceting decomposing grains (DF and FCs), CTH SP down 50cm in the F hard facet layer under the early January (0106) melt-freeze crust, which is now 1F hard, ECTP 24 in the 50cm facet layer, PST 40/100 (End) in the facet layer down 50cm. We tracked the facet layer with probes up to the Mammoth Crest and found it consistently. Test site 2 (see photo): 1125am on a NE facing slope below the Crest at 10,279' with a snow depth of 120cm- CTE PC down 10cm in the new snow, CTH SC down 70 in the facet layer under the 0106 melt-freeze crust (crust here was P hard), ECTP 24 in the facet layer (see video).

The facet layer also had moderate but clean failures in hand shears. See attached profile taken from a quick hand pit at 9200' early in our tour. The layer of concern is highlighted with a red line. This layer is made up of large, persistent grain forms and it is consistently F hard. It's grains are much larger than those of the melt-freeze layer above. The melt-freeze layer above is consistently 1F to P hard. Again the facet layer was observed between 50 and 70cm down.

It seems like, after 2 days of below freezing temps (last reading above 32 degrees F at Mammoth Pass was at 6pm on the 18th) and with lows forecasted to be between 5 and 16 degrees under clear skies tonight, we will have to again keep a close eye on our buried weak layer.

Other observations of note: Many small (D1) recent natural loose dry avalanches and several small loose dry slough results on test slopes (see photo). Calm winds below and near treeline today, but winds were light from the N where we turned around at 10,300'. No blowing snow was seen on the Crest, but on the drive home I saw a few isolated areas of blowing snow being transported onto SE slopes by NW winds at the top of the Sherwins and on Pyramid Peak, all above 10,000'.