12.8
Environmental conditions that are favorable for severe wind production from elevated/nocturnal convective systems
Morris Weisman, NCAR, Boulder, CO; and G. H. Bryan
The production of severe winds by elevated/nocturnal convection remains a forecasting challenge. By elevated, we mean convection that occurs in environments with strong static stability at the surface, such that the most unstable air is elevated. This setup is most common in nocturnal conditions, as well as on the poleward side of warm/stationary fronts. We have been investigating the conditions that are favorable for severe wind production in these environments by analyzing observations from the Bow Echo and MCV Experiment (BAMEX) and by conducting idealized numerical simulations. One favorable condition is the existence of near-neutral layers above the stable layer. Aside from being favorable for the production of CAPE, such conditions allow for the formation of cold pools above the stable layer. In some of our simulations, cold pools develop downward from these near-neutral layers. When the cold pool reaches the ground, severe winds can occur. We also find that these systems are structurally similar to bow echoes in surface-based environments, including the presence of elevated rear-inflow jets and near-upright convection at the leading edge. To provide additional guidance, we are conducting simulations in which low-level and mid-level thermodynamical variables are modified, to ultimately determine when a cold pool can be expected to develop downward. We are also exploring the conditions that favor the development of internal bores, although most of our systems (like the one mentioned above) are dominated by gravity-current dynamics. .
Session 12, BAMEX
Thursday, 9 August 2007, 8:00 AM-10:00 AM, Waterville Room
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