National Weather Center Colloquium

Southeast U.S. Cold Season Severe Thunderstorm Environments and Their Depictions Using Multiple Planetary Boundary Layer Parameterization Schemes

Ariel Cohen

School of Meteorology, University of Oklahoma
Storm Prediction Center, NOAA

17 November 2015, 4:00 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The primary goals of presented work are to identify meteorological characteristics of the southeastern U.S. cold season tornado environments and to improve numerical modeling of such environments focused on the parameterization of the planetary boundary layer (PBL). Forecasting tornadoes is particularly challenging in these environments, owing to the inherent marginal nature of one of the necessary conditions supporting thunderstorms: instability. It is hypothesized and demonstrated that thermodynamic and kinematic parameters characteristic of the near-storm environment for southeast U.S. cold season tornadoes are unique relative to other environments supportive of tornadic storms. Associated flow regimes are sensitive to small variations of buoyancy concentrated within the lower atmospheric levels. Along with unique behaviors of kinematic and thermodynamic parameters through the diurnal heating and nocturnal cooling cycles, these findings motivate the need for more thorough investigation of PBL parameterization schemes in these particular regimes.

The presentation will proceed with discussion of PBL schemes for the purpose of improving numerical modeling efforts. It is hypothesized that the incorporation of nonlocal mixing is necessary to accurately simulate the considered environments. Simulated thermodynamic and kinematic profiles using nine different PBL schemes, including ones that have been modified from legacy schemes, are compared with observed profiles for twenty one severe weather events. It is found that simultaneous representation of both nonlocal and local mixing is the most appropriate treatment of PBL processes for the Southeast U.S. cold season severe weather regime. These findings can directly benefit numerical modeling efforts for severe weather forecasting.

National Weather Center Colloquium Seminar Series website