Northern San Juan
SnowpackAndrew Temple · Apr 15, 2013 · Northern San Juan
Weather
Strong and gusty winds accompanied intermittent snowfall today to bring yet another layer of very dusty snow to the San Juans. Winds were most extreme at ridgetop level with a couple gusts knocking me off my feet. Efficient snow transport was occurring during the sustained moderate winds while high-velocity gusts were loading snow low on slopes as well as causing sublimation. High clouds were present most of the day and long-wave radiation emission was intense with new dusty snow being rapidly warmed to a very moist state with extreme rollerball activity associated with the upper few inches of snow upon skiing later in the day on a NW aspect. Temps varied from the upper 30's below TL to near freezing above TL most of the day.
Snowpack
The average HS of this zone is slightly shallower than the RMP zone, probing showed 120-140cm in paths and open trees near and above TL. Moist, isothermal snowpack to the ground except at the highest elevations. HST was in the 3-9" range depending on elevation. Dry dust deposition began likely just before snowfall early this morning and all precip. had dust associated with it forming a very dusty diffuse layer. New snow fell on an unfrozen but not too moist old-surface with a frozen layer of ice lenses just below that, allowing cohesion of the old snow, overall. Bonding at the interface seemed good where we were, although that will be subject to extreme spatial variability dependent on old-snow surface roughness/wetness. No signs of instability were noted where we were and hand shears showed resistant, non-planar shears in the top-two interfaces. One D2 avalanche was observed on a N-aspect draining into Maggie Gulch. It was an obvious cornice failure that triggered a ~1-2' deep soft-slab. The crown was only about 60' wide. There was amazing skiing during the storm (we did 4 laps), which should deteriorate quickly after the storms pass...