Lightning Density and Overshooting Tops: A Look into the Future of Offshore Storm Forecasting

The U.S. Coast Guard's primary missions include marine protection, migrant interdiction, and most notably, search and rescue. Coast Guard members respond to search and rescue cases daily, often venturing into less than favorable weather conditions to rescue mariners who have found themselves trapped in the swells of a raging storm. Thunderstorms, for example, pose a significant threat to mariners in the western Atlantic Ocean, as accurate offshre weather forecasts are often difficult to determine. Boaters often find themselves sailing directly into adverse weather, taking a large, and in some cases catastrophic, risk as they seek the safety of inland harbors. Seeking to improve offshore forecasting methods, and ultimately to provide mariners with accurate storm progression models, the National Oceanic and Atmospheric Administration (NOAA) has launched lightning density and overshooting top detection programs that will ultimately be incorporated into large-scale forecasting systems such as the new Geostationary Operational Environmental Satellite (GOES-R) and the Geostationary Lightning Mapper (GLM). Forecasters at NOAA's Ocean Prediction Center (OPC) hope to use the trends and patterns found through the course of this study to improve storm forecast accuracy in an effort to issue more precise severe storm warnings to mariners.

A myriad of case studies, focusing on mesoscale convective systems (MCS), were compiled to initiate the exploration of NOAA's new technology. These compliations consisted of historical data such as satellite and radar imagery, Historical data, including satellite and radar imagery, as well as the lightning density and overshooting top data, was compiled. This project focused on three storms, an MCS that formed in the Midwest then traveled eastwardand developed into a derecho just before transitioning offshore, an MCS that targeted the New Jersey coastline, and an MCS that traveled over the Gulf of Mexico. Analysis of these stystems used functions in the netowrk mapper (NMAP) to examine storm development, progression, and offshore bhavior. The lightning density and overshooting top data was gathered, then compared with other meteorological data, including radar imagery, ASCT/ OSCT data, surface observations, and microwave data.

Offshore storm behavior was a primary focus of the case studies, and the data collected revealed that as storms move over water, the overshooting cloud tops condensed and the lightning strike density increased greatly around these cloud tops. The cloud formations and lightning density contours, were found to closely correlate with wind and RADAR data, indicating that these programs hold the potential to illustrate weather patterns beyond the range of RADAR.

As this study continues, the focus will shift from MCS's to smaller-scale systems. Analyzing isolated convection and thunderstorms will verify the findings of the initial study, and allow forecasters to properly use this new technology. The small-scale storms will be used to verify the findings from the initial study and possibly uncover further patterns in offshore storm behavior to ultimately improve forecasting models over the open ocean.