Which correctly describes the purpose of convective SIGMETs (WST)?
A. They consist of an hourly observation of tornadoes, significant thunderstorm activity, and large hailstone activity.
B. They contain both an observation and a forecast of all thunderstorm and hailstone activity. The forecast is valid for 1 hour only.
C. They consist of either an observation and a forecast or just a forecast for tornadoes, significant thunderstorm activity, or hail greater than or equal to 3/4 inch in diameter.