Poor refreeze and potential wet slab set up on Yuba Pass.

We went to Yuba Pass today to look at overnight refreeze and wet snow development on NE aspect terrain around 7,000'. A poor to nonexistent snow surface refreeze occurred in this area last night. Weak refreeze, entirely from radiational cooling had created a breakable crust just over 1 inch thick on open slopes (photo 1). In sun exposed areas, this crust was almost fully melted by 9:45 am (photo 2). In areas under thick forest canopy, no overnight refreeze had occurred. Roller balls and pinwheels were easily triggered on steeper NE aspect test slopes (photos 3&4).

We also dug a snowpit in open near treeline terrain on a N aspect at 7,040 and found the March 24 surface hoar layer buried 10-14 inches below the snow surface (photos 5&6). Significant settlement of the upper snowpack has occurred since late March. Free water from snow surface melt had not yet reached this layer, but only had an inch or two to percolate further down to reach this layer. ECTs indicated that propagation was still possible along this weak layer. Concern exists for the possibility of wet slab avalanches to occur once free water reaches this surface hoar layer.