Fine-scale dynamical and microphysical processes of snowfall from shallow orographic clouds

May 08, 2015

Bart Geerts

Hosted by Russ Schumacher

Download Video


Light snowfall often falls over mountains long after deep frontal disturbances have passed. We use high-resolution profiling radar observations over Colorado and Wyoming, as well as numerical simulations, to explore mechanisms of such persistent precipitation from rather shallow clouds. These clouds are often convective, in which case they tend to deposit relatively more snow on the lee side of mountains, compared to stratiform clouds. Strong winds are often present and the associated boundary-layer turbulence itself may enhance snowfall in mixed-phase clouds. Radar observations show how supercooled liquid clouds over the mountains, with relatively high cloud top temperatures for significant heterogeneous ice initiation, may be glaciated by blowing snow particles from the ground up. Neither snow growth by BL turbulence nor the injection of ice crystals from below are represented in operational weather prediction models.