Thunderstorms can be a factor in cold fronts, alternatively they can be the result of instability in an airmass, triggered by heat or topography. The latter usually occur later in the day as the surface heat increases enough to send the unstable air upwards, and can be significantly more agressive in lower latitudes .
The met men have ways of measuring the lapse rates and stabilities that eyeball earthlings do not have, so there is nothng like aviation met forcasts to predict what weather will affect your flying.