How is it that there was no storm during the day, but in the morning it thunders and rains?

The mechanism for rainfall in the second half of the night and thunderstorms in the morning involves radiative cooling of the upper cloud layer. Rain in the second half of the night occurs when an unstable equilibrium develops in the upper cloud layer. It takes several hours for a cloud to develop into a precipitation cloud and rain begins to fall from the cloud formed under such conditions in the morning. A thunderstorm with some thunder spectacularly ends the convection in the middle troposphere initiated under the cover of darkness.