I know this question has an answer confirmed, but I'll add my own comments for posterity's sake. There are different types of clouds. Buoyancy-driven (cumulus-type) clouds are the types that have the most definitive bases and ceilings.
The cloud base is approximately the Lifted Condensation Level, which is the height that the air near the surface would have ...
In a sense, the full structure of a cumulus cloud extends all the way to the ground. The cloud is formed from the convection of air rising off the ground. The rising column becomes visible as a cloud when the atmospheric temperature becomes cold enough to condense water vapor, and the level where that occurs is the base we see. From Wikipedia:
You should start with NOAA services. They have a Storm Events Database going back to 1950, where you can do queries for states/counties of interest. If you are more interested in lightning data, they also have some products, including raw data from a private company (you'll need access for this) and freely available derived products.
Q: Are thunderstorms normal at the end of a heatwave?
Depends on how quickly cooler weather moves in and how moist it is.
If it's hot and a cooler damper mass of air moves in quickly (over a couple of hours) - yeeha! thunderstorms.
if it's hot and cooler weather moves in over multiple days - probably not.
I too don't know any direct sources. So you will likely have to do a bit of legwork.
Was going to offer that you could work a climatology together from
monthly FP6 reports using the desired NWS site (click the office on
https://sercc.com/nowdata.html, then switch to observed weather, then
select CF6 and choose the site and then indicate the month report ...
Physically there is no difference. A thunderstorm is defined by occurrence of lightning, no matter how much lightning there is, if it's cloud-to-ground or intercloud.
Usually if meteorologists talk about thundershowers in weather reports they want to point out that there will be weaker thunderstorms (e.g. without hail, storm, heavy rainfall or the danger of ...