Meteorology MS Seminar
Using Radar-Derived Parameters to Develop Probabilistic Guidance
for Lightning Cessation within Isolated Convection
Major Professor: Dr. Henry Fuelberg
Abstract: Daily summer thunderstorms in central Florida frequently halt outdoor operations which have to wait a certain time after an observed lightning strike to resume, especially at the 45th Weather Squadron (45WS). Prior research indicates that these wait times might be safely shortened by observing reflectivity values and hydrometeor type with radar to safely predict that lightning has ended for a particular isolated thunderstorm. We analyzed dual-polarized radar data from isolated thunderstorms to develop probabilistic lightning cessation guidance for the 45WS, which sought this lightning cessation guidance to safely shorten costly wait times after lightning strikes. We tracked 184 storms by minute in central Florida with radar and lightning locating systems including radar reflectivity and hydrometeor classification at isolated isothermal levels in addition to intra-cloud and cloud-to-ground lightning.
Following the results of other research, we investigated maximum reflectivity and graupel presence at 0, -5, -10, -15, and -20 degreees Celcius and the composite (maximum) level in an effort to develop probabilistic guidance for total lightning cessation within isolated thunderstorms. A random sample of all this data observed by minute from electrified thunderstorms was used to train a generalized linear model (GLM) to make a probabilistic prediction that cessation had occurred at that time. The most statistically significant predictors for total lightning cessation according to the GLM were maximum reflectivity at the composite and 0 degrees Celsius levels along with graupel presence at the -5, -10, -15, and -20 degrees Celsius levels. The GLM was trained with 1000 random samples of minutes to bootstrap the results, with the median values of the final set of predictors used to calculate probabilities that cessation has occurred at that minute. Forecast verification statistics from another random sample of tracked minutes were then used to analyze the performance of the GLM with different probability thresholds (95.0%, 97.5%, and 99.0%) for determining lightning cessation. Applying this cessation guidance from our GLM as though the storms were occurring in real time with these probability thresholds revealed that about 1% of the 184 storms in our data set had observed lightning after the GLM suggested cessation had already occurred, an event which would threaten life and property.
The main goal of this study was to create a usable operational tool for the 45WS for determining total lightning cessation with probabilistic guidance, a goal which is satisfied by the output from the GLM. Even the median of the most conservative probability threshold improved upon the guidance currently being considered by the 45WS, while the 95.0% probability guidance had a median wait time of just nine minutes after cessation. The 45WS has the capability to develop scans at isothermal vertical levels to put this approach into practice, so this GLM provides probabilistic lightning cessation guidance which can safely reduce long wait times after observed lightning to resume their outdoor activities.