Where can I find the average number of days with thunderstorms for each month for different locations in the United States? Does anyone know or have any links they know where it tells you that
If by thunderstorms you also mean storm events which produce lightning, you could try the Lightning Products and Services from NOAA. There are gridded products (geospatial NetCDF) and U.S. county level datasets containing "the number of cloud-to-ground lightning flashes" from 1986 to present. You might also be interested in NOAA's Storm Events Database, but bear in mind this dataset contains only severe weather events.