Environmental Factors in the Varying Length of Time between First Echo and First Tornado

The National Weather Service is charged with the responsibility of issuing tornado warnings for the protection of life and property.  Past research indicates that warning forecasters are most likely to have a negative lead time for the first tornado of an event.  One of several potential reasons is the variability in the length of time from convective initiation to the first tornado.  This study investigated numerous environmental and storm characteristics to examine the variable time-range between first radar echoes and tornado development.  A database consisting of supercells that produced the first tornado on a particular day was developed for the central and northern Plains for the years of 2005 through 2015.  Archived level-II radar data were obtained from the National Centers of Environmental Information for each supercell, and the time from initial radar echo to tornado was calculated.  Next, these supercells were characterized as either discrete,  part of a convective cluster, or along a broken line.  In addition, archived Storm Prediction Center mesoscale analysis data were obtained for each storm in the database, and a statistical analysis was completed for each variable to determine if an environmental signal was apparent.  Preliminary results indicated that storm mode, low-level moisture, and convective inhibition were the best predictors of the time from storm development to initial tornado.