2002 Annual

Thursday, 17 January 2002: 9:45 AM
Lightning Meteorology I: An Introductory Course on Forecasting with Lightning Data
Bard Zajac, CIRA/Colorado State Univ., Fort Collins, CO; and J. F. Weaver
Poster PDF (291.2 kB)
The National Weather Service (NWS) / Virtual Institute for Satellite Integration Training (VISIT) has developed a two-part teletraining course on integrating lightning data into the short range forecast process. This training is motivated by the fact that CG lightning data has been made available to NWS forecasters only recently with the deployment of the Advanced Weather Interactive Processing System (AWIPS) completed in June 1999. We review the first teletraining course which, using a mix of theory and AWIPS case studies, examines lightning activity in the majority of thunderstorms.

"Lightning Meteorology I: Electrification and Lightning Activity by Storm Scale" covers thunderstorm electrification and CG lightning activity in isolated storms and mesoscale convective systems (MCSs). The course is divided into five sections with AWIPS cases presented as part of the last four sections. Section I reviews thunderstorm dynamics and microphysics, focusing on the development of ice-based precipitation at mid-levels. Section II introduces the ice-ice collisional charging mechanism and then applies this mechanism to the lifecycle of an isolated storm. The resulting charge structure is the normal dipole with positive charge on small ice aloft and negative charge on precipitation-sized ice below. Section II also includes the first AWIPS case study, the 1997 Fort Collins flood. This case study provides evidence that ice-based precipitation is a necessary ingredient for CG lightning. It also provides an opportunity to estimate minimum thresholds in radar reflectivity structure and satellite cloud top temperature associated with CG lightning. In Section III the meteorological scenarios favoring negative and positive lightning are inferred based on the normal dipole charge structure and the charge induced on the earth's surface in response to a storm overhead. The AWIPS case study of isolated storms over Melbourne shows how the fallout of convective precipitation favors negative lightning and the development of an anvil favors positive lightning. Section IV describes the unique dynamics, microphysics, and electrification of stratiform regions within MCSs including the formation of an inverted dipole charge structure and more frequent positive lightning. The AWIPS case study of an MCS over Flagstaff illustrates the correspondence between positive lightning and stratiform precipitation. Section IV is a stand-alone AWIPS case study of an MCS/severe derecho over Des Moines. This case study tests the forecaster's ability to utilize satellite and lightning data in the absence of radar data during a warning scenario. Satellite-lightning overlays are used to diagnose MCS lifecycle and morphology (including bow echo) and areas of convective and stratiform precipitation.

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