The National Weather Service will issue a Severe Thunderstorm Warning if a storm seems to be life threatening, and could cause property damage.
To get into the specifics, you need winds gusting over 58 miles per hour, and/or hail 1 inch in diameter or greater, or a tornado. You do not need to meet all three points of criteria, but just one within a storm to be considered a severe storm for the warning to be issued. Also, lightning is not a criteria for these warnings to be issued.
Always make sure to stay up to date with the weather as we head into storm season here in Pennsylvania.