Sierra Mountain Guides Avalanche 1 course toured in the Mammoth Lakes Basin and alson at Minaret Vista today to test the persistent slab problem.
Lakes Basin: Overcast all day (OVC-) with calm winds/no blowing snow. Several CTM SP results down 10cm in F hard snow on a NNE aspect at 9800'. Same location: Rutchblock test results- RB6 MB down 50cm. Small D1 loose wet avalanche originating from under rocks on a 45 degree NE aspect at 9600'.
Minaret Vista: Field weather observation at 1040am off of the Minaret Vista Rd at 9075'- Sky= OVC-, Tair= 7 deg. C, Tsurf= -0.5 deg. C, T-20= -0.5 deg. C, Winds= Calm, gusting Light from the SW, no blowing snow. Surface was a melt-freeze crust with small surface facets. Snow depth= 133cm, Boot pen= 30cm, Ski pen= 10cm. Some sheltered areas had well developed surface hoar on N aspects between 9000' and 9200'. Persistent weak layer was observed between 30 and 60cm down on E-N-W aspects between 9000' and 9200'. Test slopes had no results, no whumphing or cracking. Snowpack tests at 9200' on a 25 degree slope, NW aspect still show potential for both fracture initiation and propagation in this layer of large (2-3mm) facet crystals: CTM SP down 20cm on what appeared to be very small buried surface hoar, CTH SP down 60cm in the facet layer. ECTP 23 down 60cm in the facet layer, PST 30/100 End down 60cm in the 20180104 facet layer. Other results were mixed: CTE RP down 7cm under the new melt-freeze crust, CMT SP down 20cm in what may be 2mm buried surface hoar, ECTN 8 down 7cm, PST results in the 20cm and 7cm layers were inconclusive.