Convective Sigmet maps cover the contiguous U.S. and are produced monthly. These maps are provided as an aid in evaluating the impact of thunderstorms on the U.S. Airspace System using the methods developed by Slemmer and Silberberg (2004). Convective Sigmets (CSIG) are issued by NOAA's Aviation Weather Center as a means of advising aircraft pilots of convective activity that is deemed hazardous ... to aviation. Convective Sigmets are text bulletins routinely issued on an hourly basis at 55 minutes past the hour, as well as times between hours (non-routine issuances) when areas of convection develop rapidly. Each CSIG is a subjectively drawn polygon, line, or circle that depicts convection whenever a specified set of criteria are met. Convective Sigmets are weather advisories concerning convective weather significant to the safety of all aircraft. Convective SIGMETs are issued for tornadoes, lines of thunderstorms, embedded thunderstorms of any intensity level, areas of thunderstorms greater than or equal to VIP level 4 with an area coverage of 4/10 (40%) or more, and hail 3/4 inch or greater.