The transfer of heat by the _____________________ in the atmosphere as a result of _____________________ caused by _________ from below. A narrow _____________________ between air masses that contrast in _________________ and/or __________________. ____________ can be caused by air rising along either warm fronts or cold fronts. The most _________________ thunderstorms develop in cold fronts. A thunderstorm is a small _____________________________________________. There are three stages to a thunderstorm are: _________, _________, _________. Severe weather is likely to occur during the _________stage of a thunderstorm. A thunderstorm that produces severe weather requires a very _________________. help